The traditional hierarchy proof in clinical epidemiology description of cases and transversal research

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1.The design of epidemiology research

The design, types and organization of research are the terms which are the synonyms of the term structure.

Under the term epidemiological research all the peculiarities of conducting the certain research, according to its plan. These peculiarities are indicated by numerous terms and only their combinations allow to reflect all the typical traits of the research. The variety of types and distinction in organization and conducting epidemiological research are represented in table 1

2.Solid research

Solid epidemiological research are the research conducted in the range of general totality, which in epidemiology is often named as the term of population. In common case the population is called the object of observation, representing all the ranges of units of observation, that possess certain characters, they are often named the characters of inclusion and exception in population. In epidemiology as has already been mentioned before, these characters are correlated to the character of time, place and “face”. The idea of solid research is connected with the desire to get the exhausting information about the phenomenon under study. The size of the population and therefore the size of solid research in scientific and routine research are significantly different. If we can accept that the aim of the scientific research is to find out the causes of occurrence and spreading of definite disease at present on the whole, and not only at a certain territory to a group of inhabitants, so the population has to be all the inhabitants who are at risk of occurrence this disease.

If the aim of scientific research is to study the causes of diseases only in a certain country or city, so the population is the appropriate inhabitants of the country or the city. Even less in the size is the general totality in routine researches, for example, while the investigation of the disease outburst in “organized” group of children. In this case population is all the children and the staff of this establishment or one or several groups, depending on the first hypothesis of the cause of this outburst .

If the aim of the scientific research is to study the diseases only in one country or city, so the population is the people who live there. Even less in the size is the general totality in routine analytical researches, for example, the investigation the outburst of the illness in “organized” children's group.

In this case the population is all the children and the staff of this establishment or one group or several groups, depending on the first hypothesis of the cause of this outburst .

In spite of the study of this case in full extend, you oughtn't to think that the results of solid research are more precise than selective. The accuracy of the data of solid research depends on many factors. For example, solid research is large scale, so in its conducting a large number of workers take place, tostandardize the qualification of them will be difficult enough and this will reflect the results of the research. The main disadvantage of solid research are the great amount of time, force and funds and as the result there is impossibility to conduct them. To overcome the disadvantages of solid researches the selective researches help, that are the main special instrument of many sciences.

Table 1 The basic terms, characterizing separate peculiarities of epidemiological research

Classification characteristic	The name of research in accordance to classification characteristic
The aim of research : · To describe the illness or other event relating to subjective area of epidemiology; · Explain the found display of the illn. and etc.	· Descriptive · Analytical (basic variants-research case- control and cohort research
General scientific method: · Observation · experiment	· observational · experimental (randomized field or clinical test)
The size of study event · the whole event (general totality) · special selected part of event	· solid · selective
The type of cognitive activity · scientific (special) · commonplace	· scientific · routine
The presence of studied events (illness, death and others) by the beginning of research: · these vents have already taken place (occur) · supposed occurrence · the cases have taken place, but the new ones are suppose to occur	· retrospective · perspective · combined
The time of conducting the research · some moment · some period	· one moment (transversal) · dynamical (longitudinal )
The place of conducting the research: · in hospital or any other medical establishment · outside the hospitals	· clinical · field

3.Selective research

Selective epidemiological research is based on the datum, got after the investigation relatively small part of inhabitants- selection. According to it the scientists make a conclusion of peculiarities of investigated case in the whole population (general totality), where this selection was formed. So the aim of selective research is to get representative information, which can be extrapolated on the whole population.

The correctness of the datum depends on the directly to the representativeness of sample which first of all defined by the right choice of general totality. Eventually the part of units of observation is selected from the general totality. According to the researcher's desire totality can be restricted to different characteristics ( time, territory, age, profession or other social or biological indication of people).

Besides the representativeness of sample is supplied by :

· the necessary quantity ( size and volume) of sample;

· keeping the principle of randomization.

The quantity of sample depends on many components and in the first place it is the character of research. If the aim of the research is the estimation of disease among the population, so it is necessary :

· select (put) the degree of reliability of measurement of disease i.e. the deviation value of selected datum in the studied population;

· to know approximately the frequency of illness, which can be found.

If the number of population is unknown the size of the sample can be calculated with the help of the formula:

If the size of the population is known the size of the sample can be calculated according to the formula:

where ( for both formulas)

n- is the sought-for number of sample;

N - the number of population;

t- validation criterion;

I - supposed frequency of disease incidence;

q = (R-I) , where R - is used regularity of the indicator for I;

Д- chosen maximum of error of the indicator. As a rule a permissible error comprises not less than 25% from the size of indicator I.

Let us suppose that in the town N the scientists are going to conduct cross-sectional study with the aim to study the frequency of arterial hypertension disex15 400ase among the men at the age of 20-29. The quantity of this group in the town of N is 15 400. According to the datum of research which was conducted several years ago, the frequency of disease made up 70 % o( I=70,0%) Consequently, Д is 25% from 70,0 i.e. Д=(25x70,0) / 100= 17,5 %o.

= 306,2% o - as a result n = (70,0x(1000-70,0) x 2x15 400)/ (15 400x 306,2) + (70,0 x (100000-70,0) x2) = 806 people. So for getting sample data relevant to necessary reliability, from 15 400 men at the age of 20-29 it is necessary to study 806 men.

The second condition for getting the representative sample is the principle of randomization ( from English random which means case). Randomization supplies occasional selection from people representing general totality. In other words randomization is the equal chance to every unit of observation from the general totality to get into a sample which decrease the danger of unpremeditated misrepresentation of the structure of sample, but can't totally exclude untrustworthy of the researcher during its formation.

The observance of the principle of randomization is achieved by different types of forming sample. The Choice of selection depends on:

the design of research;

supposed accuracy of results;

the volume of general totality;

the possibility to use the most accurate method and other objective and subjective causes.

Nowadays the ideal principle for randomization is considered the usage for sample the units for study the tables of random numbers or similar computer programmes. This type provides nonrepeated sample when the unit is selected only once. Such approach is obligatory for forming trail and control group during the conducting the majority different means and types of curing the patients. It leads to maintenance of the principle of unprejudiced research and minimizing the unpremeditated misrepresentation the components of group. And at great degree supplies safe conclusions. However any design can't totally exclude the dishonest specific researcher.

The other types are based on the certain planning in selection of the units of observation, that naturally definite planned in selection of units for observation that naturally decreases maintenance of the principle of randomization.

4.Mechanical sample

At the beginning the units of observation are placed according the order of some occasional characteristic: the number of medical report, case history, the first letter of the last name and so on. Then it is necessary to define the interval at which the units of observation will be mechanically chosen from the list of general totality. (For example very fifth) For identification the interval the number of general totality is necessary to divide into the number necessary for the sample.

epidemiological population terminology

5.Typological (typical) sample

At the beginning the general totality is divided into groups according to one typical character. More often different individual different characters are used such as age, profession, influence of supposed risk factors, diseases, and so on. Next the necessary number of observation units are selected by occasional or mechanical method. The number of sample from each group must be determined beforehand and correlation between the structures of samples of each group (for example according the age) must correspond to the structure of general totality. Such kind of sample is often called reasonable typological sample. This method is used more often in observation analytical reaches.

6.Serial (cluster) selection

Serial (cluster) selection is similar to typical. The difference is that during the serial selection not separate units but whole groups are chosen from the general totality by random type , which are called series or clusters. Clusters may be separate establishments, shops, medical locality, in-patient departments, wards etc. After that in every cluster the solid research of all the units of observation is conducted.

7.The method of purposive selection

The method of purposive selection supposes to exclude from analytical research some factors the influence of which is well known on the stage of defining. For instance, the influence of smoking on the risk of developing cancer is well known, but it is not the only factor. So the researchers, taken am aim at to find other additional risk factors of lung cancer, shouldn't include in the general totality and as a result in selection smokers. The advantages of selective sample over solid one is that at the proper organization reliable data can be collected, spending less time, funds and manpower. During the testing researches at the expense of their less volume it is easier to control getting the unified information and to minimize the errors. At the same time due to objective causes in many researches so called joined samples are studied, which have insufficient representation to the whole population and this is necessary to take into consideration evaluating the conclusion of such research.

8.The characteristic of some terms, defining the design of epidemiological researches

Descriptive researchproposes obtaining descriptive epidemiological data i.e.data of disease activity. Such research can be self reliant, but obtained new descriptive epidemiological data impel researchers to further research to explain found display of disease.. So descriptive research is as a rule only the first part of full of value epidemiological research and the analytical part is also included.

Analytical researchis devoted to exposure the causes of appearance and spreading of the disease. The process of searching corresponds to general scientific presentation of two acceptings ( ways) of revealing the connections between the supposed cause and the consequence. The first way is from consequence to cause. Using this the researcher departs from the establishedconsequence ( for example disease), and tries to find the event in the past which can be examined as the causes of this consequence. The other accepting is from the cause to consequence. Orienting themselves on supposed cause, the researchers expect the appearance of casual conditioned consequence.

9.According to the acceptings of search two types of analytical researches are developed : case control and cohort research

The research of case control is an analytical retrospective research the aim of which is to find risk factors of examined disease. The main group is selected among the patients of studying disease, control group consists of people, who don't suffer this disease. The fact of influence on examining factors is defined by questioning of people in comparing groups, their relatives, and archives data. The comparison of the frequency of meeting particular facts in main and control group allows to calculate the indicator of ratio of chances (OR), according the size of which the presence of cause consequence relationship is evaluated.

Observation research doesn't involves interference in natural process of occurrence and spreading of the disease. We can include the research of morbidity in the situations, when interference is the obligatory practice. For example, the routine study of infection morbidity, conducted by immunoprophilaxis.

During the experimental research visa verse itis supposed controlled and reproducible interference in natural development of the disease with the aim of defining the cause of it. At the same time epidemiological experiment is due to corresponding to other scientific demands to any other experiment. Thereby the terminology used by some authors such as “natural”, “uncontrolled epidemiological experiment” are incorrect. As the result of any experiment it is necessary to give the answer to the question, why it happened in such way, any experimental research is always analytical.

10.Scientific( special) research is organized specially to get (to coferm) new data

Routine research is considered any epidemiological research, appropriate the professional duties. It is supposed to get new scientific data, visa verse routine research is conducted in the frame of existing at present scientific conceptions of the cause of appearance and spreading the disease.

Retrospective research is based on the study of the information, about the appearance of the disease for a certain period of time in the past, and the first type of search the search of cause consequence relationships is used- from the cause to the consequence. The main source of the information is the existing system of registration and calculation of patients. Retrospective research can be as descriptive so analytical.

Perspective research considers to study the information as new cases (“fresh”) appear, which weren't at the beginning. The study of cause consequence relationships is based on the second type- from cause to consequence. The study is based on the probability of occurrence of new cases of disease (consequence) among the group of population, influenced by the factor of risk (cause). Perspective research is only analytical.

One moment (diametrical) research can be as descriptive so analytical .That is probably why in different epidemiological editions they are rated either to descriptive or analytical research In any case the main aim of these researches is to get information about the catching illness of the population by any disease during the restricted period of time, and such kind of study can be repeated if necessary. As the one moment study is supposed to find all cases of disease, existing at the moment, the research is also called the research on the prevalence ( affected), and the results of one moment research are often shown in the index of PRM.

If the revealed casesconnect with some factor of risk, the study can be analytical.

Dynamic (lengthwise) research foresees systematic study the information about falling ill within the same group of inhabitants. At the same time the research can be permanent or repeated in short periods of time. The typical example of dynamic research is routine operative and retrospective analysis of falling ill of the population, which is conducted by the specialists of sanitary hygienic supervision.

Though the notion “clinical” is connected with the place of provided epidemiological research, it is used only with the aim to indicate the experiments that are taking place in the hospital in order to estimate the effectiveness of medical drug, the types of diagnosis, and the schemes of curing the patients.

The field is considered the study , which takes place outside the medical establishment. Its sizes are rather various, beginning from a small outburst to a national research. The field research can be:

descriptive and analytical;

observational and experimental;

solid and selective;

routine and scientific;

retrospective and perspective;

one moment and dynamic.

No one of mentioned above can independently expose all the peculiarities of conducting the epidemiological research. For example, the study of the outburst of any disease is not only observational, but also simultaneously analytical, and more often routine, solid, one moment, retrospective or combined clinical or field research.

The organization of the research is a coordinated, ordered, interconnected totality of different actions, leading to the achievement of marked aim. It consists of several stages :

preparatory;

collecting the information and first statistic arrangement;

statistic and logical analysis of the information which is collected;

formulation of conclusions ( the final stage).

The preparatory stage includes:

· explanation of topicality (necessity) of conducting the research;

· formulating the final and intermediate aims;

· formulating the working hypothesis;

· the selection of the objectand the units of research ;

· completing the programme;

· writing the plan;

· conducting the pilot research.

The majority of epidemiological researches foresee the achievement of analytical aims i.e. are aimed to find the causes of appearance and spreading of studied pathology. So the first part is the descriptive part. Not less important are the researches devoted to the evaluation potential effectiveness suggested means and types for struggle with spreading the disease. In practice they find not only potential effectiveness but also the real quality and effectiveness of executive activity. According to the data, which were obtained after the analysis of literature and the marked aim the working hypothesis is defined- supposed explanation of studied event. For example the hypothesis of the causes of appearance and spreading is not fully studied disease or ( for routine research) hypothesis of the cause outburst of any disease, but in the net work of known to the science possible causes of its appearance. The workinghypothesis defines all the following actions and the main part of the design study. In the course of the research new correction can be brought to the working hypothesis but if this brings to the change of the programme the research should be started again.

The object of study (observation in epidemiological research are the groups of comparison, which are called differently in different researches:

exposed and non-exposed;

The healthy and the ill ;

Basic and controlled;

Experimental and controlled and so on.

These groups consist of the patients and healthy people- they are the units of observation, each of which is to registered. It is extremely important as in scientific so in practical research at the preparatory stage define the criterion when a person will be consider sick., that is to formulate the indications of standard case of concrete disease. Sick and healthy people (the units of observation) are the bearers of different signs. Those signs which are supposed to take into consideration (register) are called registration.

The programme of research includes the programme of collecting information and the programme of summery and grouping of data. The programme of collecting the information is a registration document, existing or specially designed, where the list of registration characteristics, necessary for fulfilling intermediate or final aims, is represented. Registration characteristics are used in the following stages for classifying received data, so they are classifying characteristics. There different classifications of registration (classifying) characteristics.

The main epidemiological classification of classifying characteristics is based on the separation :

· Diagnosis;

· Characteristics of time;

· Characteristics of place (territory)

· Characteristics of “face” ( individual characteristics)

With the help of such characteristics it is possible to make different groups of sick and healthy people. Besides the mentioned classifications registration characteristics are divided particularly into factor (factorial) and effective. Factor are the characteristics under which influence the condition of man's health differ. Effective characteristics are the different estimations of man's health conditions.

The division of registration characteristics into factorial and effective must be substantiated by working hypothesis of reason consequence relationships of supposed risk facts and morbidity. Not often all the characteristics are divided into related to the unit of observation that is sick or healthy person and they are called host factors and into the characteristics of habitat that is environmental factor.

In every registration document besides registration characteristics the “passport “ part is necessary. There is :

The number of registration of the document (the unit of observation);

The date of filling in;

The number of insurance police;

ID;

The name and surname of the patient (sick or healthy);

The age and other necessary for any researches data.

The registration document finishes with the signature of the person who filled it.

The programme of summery and grouping of the data is the set of model tables, which are often called developed. They are supposed to use during the second stage of research. Registration characteristics will be written there from registration documents. The model should represent all the peculiarities of studied occurrence, which are supposed to find. So the models of tables have to correspond with the aims and working hypothesis of research.

Working out the models is not only technical work but also mainly purposeful, considered actions. It is necessary to choose group characteristics necessary to make the concrete tables. All three types of statistic tables are used in epidemiological research .They are simple, group and combined.

The plan of the research is a document where all the main actions are reflected, which are necessary for achieving the aim. At the same time it is necessary to show the time place and technical means, staff, the level of their training, the period of fulfilling some actions and so on. And as the result the design of certain epidemiological research is defined which can help to conduct the set aims.

Nowadays a great attention is paid to conducting so called pilot ( testing, approximate) research .

Pilot research in particular let us :

Specify the aims and working hypothesis;

Specify the programme of collecting of information and models of tables;

Check the types of collecting information and the methods of its study;

Estimate the training of the staff;

Get the idea of variety of registration characteristics;

Evaluate the choice of design of research;

Specify the volume of necessary means and power;

Specify the time of conducting.

11.The stage of collecting information and its first statistic processing is important

The processing of the information means the process of achieving necessary data and filling registration documents. It is important to follow strictly follow the designed programme of collecting information, and try not to break the rules of selecting units of observation, exclusion registration characteristics, changing the types and methods of collecting information. During the process of collecting information its quality is evaluated from time to time, the keeping to the rules is controlled. The collected information is grouped and put according to the modal tables. Such actions are called first statistic defining of research data.

The duration of this stage depending on the design of research varies from some hours ( investigation of outburst) to decades of years (perspective cohort research)

In common case the collecting of data goes on as far as it is necessary to get the necessary volume of information, stipulated by the programme of research.

The final stage of epidemiological research includes further statistic and logical proceeding of the received information, the organization of received epidemiological data and the description of the research, formulating the conclusions (findings)

The further - after summering and grouping- statistic proceeding of data can be very various and include a great number of statistic methods. These methods allow factually and thoroughly describe the dynamic and the structure of the disease and also measure ( but not find) reason consequence relationship between supposed factor of risk and the illness. In spite of various statistic methods, the choice of concrete method has to be strictly statistically and logically based. The breach of this rule will lead to wrong conclusions.

For study of collected information and presenting the results of research a big importance is so called organization of epidemiological data, i.e. their table and graphic reflection. During the final stage new tables are made, where the results of statistic evaluation of different comparative size is presented.

The graphic reflection of received information let demonstrate mentioned in the table the peculiarities of dynamic and structure of studying phenomena. But it is necessary to take into considerations that if diagrams are built wrongly that leads to fully mispresent the regularity presented in the table.

The description of the research ( report) means the detailed reflection the whole process of work.

The formulation of conclusions is based on the results of statistic and logical study of collected information.

12.Case control research

The aims of the research of case control is to define the reasons of emerging and spreading of disease. In case control research the probability of existence of reason consequence relationship is based on not on the different occurrence of the illness, but on different spreading ( popularity) supposed risk factor in bacis and control groups.

In the case control research the search of reason consequence relationships goes in the direction from consequence to supposed reason (fig.1)

Fig 1. The way of searching reason consequence relationships in the case control research

Case control research can be retrospective only as it is conducting only on achieve data. More often the source of information in case control research are medical histories from medical achieves of medical establishments., the recollections of patients or relatives within the interview or as the result of questionnaires.

Such kind of research can be conducted as preliminary research of reason consequence relationships between supposed risk factor and concrete disease.. In future this problem can be studied in cohort research.

13.The stages of case controlled research

The study of case control (fig.2) so as the cohort research begins from the defining the general totality i.e. the part of populationthat will be studied. The criteria of inclusions and exclusions are taken into consideration, which are defined at the preparatory stage. Here we can put the individual characteristics if potential participants, such as sex, age, the race, the place of work, bad habits and so on. The territory of inhabitance is very important too for the group of population and the time of exposure of negative factors.

Then they form the selection. In case control the participants are taken who have certain pathological state.

Fig 2 The algorithm of selected research of case control

Those people will be represented in main group. The control group will be formed from correlatively healthy people who don't have the studied disease. So the selection in cohort research consists of half of sick and half of healthy people.

One of the methods of forming the group - the main and the control, is the method of selection of pairs. The contain of such approach is in individual selection to each participant of main group the participant of controlled group with taking into consideration the rate of measurements such as anthropometrical, sex, social, ethnical and other distinctive characteristics. As the result the researchers get approximately similar groups for comparison with the only distinction : absence or presence of studied disease.

The next stage of research is to define in main and control groups the people who were influenced or were not influenced by supposed risk factors.

After that the data about the presence or absence of studied factor put into the table of conjugation ( four level table) (table 3-5). This stage of division of main and control into sub groups ( a F +, b F-, c F+ and d F- ) can be repeated several times as many times as the number of risk factors during the study of archive data was found.

According to the rule of making tables they point the subject groups: in the main group there are the people with the studied disease, in the control group there are relatively healthy people. The criteria which conducts the comparison of the members of groups are recorded into column.

The final stage of the research is a statistic and logical analysis of received data and formulating of conclusions.

The statistic processing of received data in the research of case control

Table 2 The model of four level table for case control research

group	Risk factor in medical anamnesis	Total
	presence	absence
The patient suffering from studied disease	a	b	a+b
Healthy or sick people who have another disease	c	d	c +d
total	a+ c	b + d	a+ b+ c + d = N

As it is impossible to calculate the indicators of incidence and relative risk in case control research, evidence of reason association in case control research is defined by the difference in the frequency of influence ( the frequency of unit popularity) risk factor in comparing groups , but not in the frequency of incidence of disease in comparing groups.

The frequency of influence ( frequency of unit popularity) risk factors in these groups are calculated by the same formula as the absolute risk in cohort research i.e. a / (a+b) - for the main group (case) and c / ( c+d) - for control group. The calculated frequency of influence shows the meaning of probability of influence of the factor under study in compared groups. The further calculations of chances are conducted according the algorithms, examined in the example in cohort research.

The lite formula of calculation is the following :



But there difference between the indicator of relations of chances which were got in cohort research and case control research. In cohort research they calculate the relation of chance to fall ill at the presence or absence of risk factor while in case control research the control is estimated by the relation of meeting supposed risk factors among sick and healthy members.

In case control research the calculation of indicator of aetiological part is possible by using the formula:

In this situation the indicator shows unit weight of number of cases of influence of sought-for factor which leads to the disease under study.

The estimation of reliability of the difference in the results of research in case control in comparing groups is conducted with the help of criteria , used in cohort research ; they calculate confidential intervals for Pierson's criteria ( he square) or precise criteria of Fisher.

14.The advantages and disadvantages of case control research

The positive aspects of case control research is the following- the possibility of its conducting independently from the spreading of the disease under study. Comparatively small amount of time, power and funds are necessary for creating main group of patients ( even seldom happening disease) , selecting a control group for the main one, questioning the patients and making at least approximate conclusion. While conducting the study in cohort research they will have to select the cohort consisting of one thousand people , watch them for a long time. It involves remarkable time, money and moral expenses.

Research case control has relatively short duration. The duration of the research depends directly on the staff's productivity, who take part in the research. For receiving the conclusions it is not necessary, as it is in cohort research , to conduct the observation during the period that is more than latent period of development of the disease.

There is an opportunity to find simultaneously several factors of risk of one disease.

For the case control research relatively small economical expenses are typical. This makes them attractive in the case when the researcher is restricted financially. But it is necessary to keep in mind that each research has its own restrictions and indications.

In case control research it is impossible to expose rarely occurred causes of disease. In such cases the insufficient data don't allow to evaluate the trustworthy of difference of frequency of occurrence of risk factors of the disease in the groups of comparison and as a result to make a conclusion about the presence of reason consequence connection.

One more disadvantage of this research is the impossibility to evaluate the occurrence of risk of appearance the disease (death) in quantity from the supposed disease. During the research it is possible to measure in quantity the indicator of “relation of chances”. As a result the researcher get low reliability of conclusions because of high liability of systematical errors.

15.Cross-sectional study ( the research of distribution, one moment research)

The aim of cross-sectional study (one moment) research is to describe the interconnections between disease ( or other condition of health) and the factors, existing in a definite population at concrete time and making as positive so negative influence on people. One moment research is often forms the basis for solution in effective management in public health. It allows to renovate the data of state of health of separate contingents by conducting the research of small groups of inhabitants. This research can be done at a definite time, but collected data may concern events in the past ( for example, the examination of patients' case history with the aim to examine how often the blood pressure was measured for the last six years). Within transversal research they evaluate popularity ( prevalent ness) of cases of diseases and popularity of risk factors and also evaluate their combination

Fig.3 Comparative characteristic of three analytical research : cohort, case control and cross-sectional study

In the picture 3 the comparative characteristic of three analytical research : cohort, case control and transversal is presented. As opposite to cohort research and case control research ( longitudinal researches) , transversally conducted research is a research conducted relatively to time axis ( risk factors and diseases are studied simultaneously) .

The stages of conducting cross-sectional study

· Formation of selection (cohort) from general totality taking into account the indications of presence and absence ( fig.4). The selection must be representative in quality and quantity.

· The collection of information of popularity of risk factors and disease. Each member of the process undertakes the medical examination with the usage of physical examination, laboratory tests and necessary methods of functional diagnosis. As a rule the specialists find out the influence of risk factors on patients from the patients themselves, trusting their memory and awareness. They make the collection of industrial anamnesis, information of social and economical status of the members, their heredity and so on.

· As the result of one moment examination of selection (cohort) they form four groups of participants :

Fig.4Algorythm of conducting transversal research

0 sick people influenced by the factor under study;

0 sick people are not influenced by the factor under study;

0 the group of healthy people definitely influenced by the factor under study;

0 the group of healthy people who are not influenced by the factor under study.

· Description of clinical presentation of disease and also ascertain the cases of influence of supposed factors of risk.

· Formulating the hypothesis about risk factors and diseases and their interconnections.

· The calculation of indications. Within one moment examinations as it was mentioned above, the indicator of prevalence(popularity) is calculated . Depending on the quantity of observations over the cohort, the possible calculation of indicator of the period (PR) and moment prevalentness (PRM) is:

Where A is a number of all the sick people- members of examination, with single occurrence the indicator is PRM, with repeated occurrence the indicator is PR.

N is a quantity of selection

R is dimension.

· The evaluation of trustworthy of difference

The advantages of research

· It describes the clinical presentation of disease with the simultaneous registration of the factor of influence on examining cause.

· The plain algorithm of conducting.

· Informativeness.

· Low economical expenses.

The disadvantages of research

· The absence of group of comparison.

· It is impossible to establish reason consequences connection as within transversal examination they don't get direct data about the consequence of events.

Example

As a result of transversal examination it was found the over weight was diagnosed among the women who suffered from arthrosis and consequently is less met among those who don't have this disease. Could over weight influence on excessive load on joints and as the result the arthrosis develops among the women or visa verse the women witharthrosis had low physical activities and as the result they had over weight? To answer these questions through transversal examination is impossible ! This type of research is unfit for the analysis of prognosis as in the examination of the popularity it is impossible to indicate the frequency of occurrence of new cases of disease ( as in cohort examinations) and so the indicator can't be used for calculation for probability of occurrence of the same event with the people having similar characteristics in future.

Situational tasks

Task 1 Indicate the correspondence of the questions more suitable for the solving epidemiological research:

1. case control research;

2. one moment examination.

Questions:

a) Does the inclination of body during the sleep the risk of sudden death of a baby;

b) Does the vaccination against hoping cough bring to damage of brain tissue;

c) What happens with the prematurely born baby in some years after the birth and what is the further physical development and the success in study;

d) How do the nurses trust the effectiveness of electroshock therapy to the patients with heavy depression;

e) Is there a connection between the high voltage line and the beginning of leukemia;

f) Does the usage of peroral contraceptives lead to breast cancer;

g) Does the smoking lead to lung cancer;

h) Is it true that half of cases of pancreatic diabetes are not diagnosed still;

i) Does the high blood pressure become normal within time;

Task 2. The question for case control research ; Does the usage of meclofenamate sodium lead to the risk of kidney disease?

· What additional information it is necessary to get?

· Prepare the scheme of epidemiological research.

· Comment every stage of epidemiological research.

· What indicators ( coefficient, quantities) can be calculated as the result of this research?

Final control of knowledge

Choose one of the right answers

1. What indicators are calculated as the result of case control research :

a) relationships of chances;

b) relative risk;

c) attributive risk;

d) Pierre's criterion.

2. The case control examination is common :

a) low probability of getting error results as it is possible to create representative selection of “experimental” and “control” groups

b) relatively low expenses;

c) relatively short time of examination;

d) the possibility to get approximate conclusions from a small selection.

3. Priority areas of using epidemiology research case control examination

a) rarely met disease;

b) rarely met reasons of disease;

c) different consequences of one reason;

d) one consequence of different causes.

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