1. Classification of epidemiological methods

Epidemiological research methods are generally divided into observation methods: including descriptive epidemiology and analytical epidemiology; Experimental method, also known as experimental epidemiology; Mathematical method, also known as theoretical epidemiology.

2. The basic content of epidemiological research design

(1) Consult relevant literature and put forward the research purpose.

(2) Determine the research content according to the research Et.

(3) Choose research methods according to specific conditions.

(4) Determine the research object according to the research method (the relationship among target population, source population and research object should be distinguished).

(5) Design the survey form according to the research content.

(6) Control the research process to ensure the research quality.

(7) Straighten out the analysis ideas and draw a correct conclusion.

② Descriptive epidemiology

1. Describe the concept of epidemiology

Descriptive epidemiology is also called descriptive research. It is an observational study that groups the data obtained from special surveys or routine records according to the characteristics of different regions, different times and different populations to show the distribution characteristics of diseases or health conditions in this population. Special investigations include: current situation investigation, ecological investigation, case investigation and epidemic investigation; Routine records include: death report, birth registration, birth defect monitoring, adverse drug reaction monitoring and disease monitoring. Descriptive epidemiology can; ① provide clues for etiological research; (2) Grasp the distribution and etiology of diseases, and provide basis for disease prevention and control; ③ Used to evaluate the effect of control strategies and measures.

2. Present situation research

Also known as cross-sectional study or prevalence study, it is the most widely used method in descriptive research. It exists in a specific group of people. Collect data of diseases, health status and related factors at a specific time and population through general survey or sampling survey, and describe the distribution of data and the relationship between diseases and factors. According to the purpose of the study, the current research can adopt general survey or sampling survey.

(1) Census: A survey of every member of the population at a specific time and within a specific range. The general survey is divided into two parts: the general survey aimed at understanding the epidemic situation and health status of the population and the screening aimed at early detection of patients.

(2) Sampling survey.

1) the concept of sampling survey: a representative part of people (samples) are randomly selected from the population according to a certain proportion for investigation, and the parameters of the population are estimated through sample statistics, which is called sampling survey. Sample representativeness is the key to the success of sampling survey, and random sampling and appropriate sample content are two basic principles to ensure sample representativeness.

2) Sampling methods: simple random sampling, systematic sampling, stratified sampling, cluster sampling, multi-stage sampling, etc.

3) Estimation of sample content: In sampling research, the number of research objects contained in a sample is called sample content. Appropriate sample content is the basic principle of sampling survey. Appropriate sample size refers to the minimum sample size required to control the random error of the sample within the allowable range. The calculation method of sample content includes the estimation method of sample content of classified variable data and the estimation method of sample content of numerical variable data (see related textbooks for details).

(3) Analytical epidemiology

1. The concept and classification of analytical epidemiology, also known as analytical research, is a research method to further observe the relationship between suspicious causes and diseases and health status in selected populations. There are two main epidemiological analysis methods: case-control study and cohort study, both of which are to test the hypothesis of etiology. Evaluate the role of risk factors.

2. Case-control study

(1) Concept of case-control study: Case-control study is an observational research method. People with and without specific diseases are selected as case groups and control groups respectively, and the proportion or level of past exposure of each group of people to one or more suspected risk factors is investigated. By comparing the differences in the proportion or level of exposure of each group of people, it is judged whether the exposure factors are related to the diseases studied and the degree of correlation.

Case-control study has the following characteristics: ① This study is an observational study, which only collects the exposure of the subjects objectively and does not give any intervention measures. ② Case-control study can trace the past exposure history of suspected risk factors, and its research direction is retrospective, from "cause" to "inducement". ③ Case-control study is divided into groups according to whether there are diseases or not, and research factors can be set arbitrarily according to needs, so as to observe the correlation between a certain disease and various factors.

Case-control study can adopt the following methods: ① Preliminary test of etiological hypothesis; (2) Put forward the clues of etiology; ③ Evaluate the effect of prevention and control strategies and measures.

Case-control studies are divided into mismatched case-control studies and matched case-control studies (also divided into frequency matching and individual matching).

1) unmatched case-control study: that is, a certain number of research objects are selected from the case and the control population respectively. Only the control number is required to be equal to or greater than the number of cases, and there is no other provision.

2) Paired case-control study: ① Definition: It is a restrictive method that takes some variables that interfere with the research results as paired variables and requires the control group and the case group to be consistent in paired variables. Matching is divided into frequency matching and individual matching.

The purpose of matching: First, to improve the research efficiency, that is, the amount of information provided by each research object increases, and the required sample content decreases; The second is to control confounding factors and avoid confounding bias in research. ③ Precautions for matching: The matched variables must be known confounding factors, or there are sufficient reasons to suspect that they are confounding factors, otherwise they should not be matched.

(2) Selection of research objects: As this kind of research is generally a sampling survey, it is required that both cases and controls should be random samples of their population.

1) The selection of cases needs to be considered: ① diagnostic criteria of diseases; ② Time of diagnosis. ③ representativeness of cases; ④ Limitation of some features of the case. The source of cases mainly comes from hospitals and communities.

2) Selection of control: Control refers to the people who have not suffered from the studied disease in the population where the case originated. When selecting control, we should consider: ① determining control standard; ② representativeness of control; ③ Comparability between control and case; ④ The control group should not suffer from other diseases related to the studied factors; ⑤ Sometimes you can select two or more controls at the same time. Source of control: ① Cases of other diseases diagnosed in one or more medical institutions; (2) people in the community who have never suffered from the disease; (3) people who have not suffered from the disease nearby; 4. Spouses, compatriots and relatives; ⑤ Colleagues in the case.

(3) Estimation of sample size of case-control study: there are estimation of sample size of classified variables in unpaired case-control study and estimation of sample size of classified variables in paired case-control study (please refer to relevant textbooks for specific calculation methods).

(4) Statistical analysis of case-control study data: Case-control study uses ratio to estimate the intensity of association between exposure and disease. Odds refer to the ratio of the possibility of something happening to the possibility of not happening. This ratio is the ratio of the exposure ratio of the case group to the exposure ratio of the control group.

(5) Advantages and limitations of case-control study.

1) Advantages: ① This method is more convenient to collect cases and more suitable for the study of rare diseases; (2) This method needs fewer research objects, saves manpower and material resources, and is easy to organize; ③ A survey can study the relationship between a disease and multiple factors at the same time, which can not only test the hypothesis of risk factors, but also put forward the hypothesis of etiology through extensive exploration; ④ After collecting data, the results can be obtained in a short time.

2) Limitations: ① It is not suitable to study the factors of low exposure rate, because it requires a large sample content; ② The time sequence between exposure and onset is often difficult to judge; ③ Selection bias is easy to occur when choosing research objects; ④ Memory bias is easy to occur when obtaining past information; ⑤ It is easy to produce mixed bias; ⑥ The morbidity and mortality cannot be calculated, so it is impossible to directly analyze the relative risk.

3. Queue study

(1) the concept of cohort study: cohort study is to divide a well-defined population into different subgroups according to whether they are exposed to a suspicious factor or exposure degree, track the results of each group and compare their differences. Therefore, it is an observational research method to judge whether there is correlation between exposure factors and outcomes and the degree of correlation.

(2) The purpose of cohort study is to test the hypothesis of etiology and describe the natural history of the disease.

(3) Classification of cohort studies: According to the time when subjects entered the cohort and the observation ended, cohort studies can be divided into prospective cohort studies, historical cohort studies and two-way cohort studies. According to whether the research objects in the queue are relatively fixed or constantly changing, they can be divided into fixed queues and dynamic crowds.

(4) Selection of research objects

1) Selection of exposure group: It is required that the subjects in the exposure group should be exposed to the research factors and provide reliable exposure and prognosis information. For example, special exposure groups, general groups or organized groups can be selected according to the situation. If necessary, the exposure groups can also be divided into subgroups with different exposure levels. The exposure group has the following options.

2) Selection of control group: The control group of cohort study should be all or randomly sampled non-exposed people in the exposed group. In addition to the research factors, other factors related to the results should be balanced and compared between the exposed group and the unexposed group. There can be internal control, external control, total population control and multiple control.

(5) Estimation of sample size: The sample size estimation formula used in the cohort study is the same as that used in the case-control study, but the cohort study compares the incidence of outcomes, so P0 and P 1 are the incidence of outcomes in the non-exposed group and the exposed group respectively. (Please refer to relevant textbooks for specific calculation methods. )

(6) Statistical analysis of cohort study data: In cohort study, the most concern is the intensity of diseases caused by exposure factors-incidence rate, including cumulative incidence rate and incidence density. Relative risk, attributable risk, attributable risk percentage, population attributable risk and population attributable risk percentage are usually used to estimate the intensity of correlation between exposure and morbidity. In addition, when the morbidity (mortality) rate of the whole population is compared, the standardized morbidity (mortality) rate can be calculated.

(7) Advantages and limitations of cohort study.

1) Advantages: ① The research conclusion is obtained by personal observation and is generally reliable; ② Strong ability to demonstrate causality; ③ The incidence of exposure group and non-exposure group can be calculated. The intensity of association between exposure factors and morbidity can be directly estimated; ④ A variety of results can be observed in one survey.

2) Limitations: ① It is not suitable for studying diseases with low incidence; ② The observation time is long, which is prone to deviation. (3) It consumes a lot of manpower, material resources and time; ④ High design requirements and complicated implementation; ⑤ During the follow-up, the introduction of unknown variables or the changes of known variables in the population will affect the results and complicate the analysis.

4. Experimental epidemiology

(1) The concept of experimental epidemiology: Subjects from the same population were randomly divided into experimental group and control group, with experimental factors given to the experimental group and no such factors given to the control group. Then the results of each group were followed up prospectively, and the degree of difference was compared to judge the effect of experimental factors.

(2) Basic characteristics of experimental epidemiology: ① Intervention measures should be taken; ② Prospective observation. ③ There must be parallel control; ④ Random grouping.

(3) Classification of experimental epidemiology: it can be divided into field trials and clinical trials. Field trials are also divided into community trials and individual trials. When an experimental study lacks one or more of the three characteristics of prospective observation, parallel control and random grouping, it is called quasi-experiment or quasi-experiment.

(4) The concept and design of clinical trial.

1) Definition of clinical trial: It is a prospective study in which clinical patients are randomly divided into experimental group and control group, and the experimental group is given certain clinical intervention measures, while the control group is not, and the effect of clinical intervention measures is judged by comparing the effects of each group.

2) Clinical trial types: it can be divided into randomized controlled clinical trials, non-randomized controlled clinical trials in the same period, historical controlled clinical trials, self-controlled clinical trials and cross-design controls.

3) The determination of the research object should consider: ① the diagnostic criteria of the research object ② the representativeness of the research object; (3) Candidates and exclusion conditions of the research object; ④ Medical ethics; ⑤ Estimation of sample size.

4) Random grouping of subjects: The purpose of random grouping is to randomly assign subjects to the experimental group and the control group, so that the control group has similar clinical characteristics and prognostic factors, that is, the two groups are fully comparable. Commonly used randomized grouping methods are: simple randomized grouping, block randomized grouping and hierarchical randomized grouping.

5) Control group: there are blank control, placebo control, standard treatment control, and different doses, different courses of treatment and different routes of administration.

6) Data collection process requirements: blind observation (single-blind, double-blind and triple-blind), standardize observation methods, and improve the compliance of research subjects.

7) Common analysis indicators: effective rate, cure rate and survival rate.