Concept: A research method that divides people into exposed groups and non-exposed groups according to whether they are exposed to the research factors. After a period of follow-up observation, the difference in morbidity or mortality between the two groups is compared to determine the relationship between the exposure factors and the disease. .
Research direction: cause→effect
Classification:
Fixed queue: In prospective observation, if the research subjects enter the queue at the same time (at a fixed time or within a short period), no new members join during the observation period, and almost no members withdraw until the observation is terminated, the queue remains unchanged during the observation period. Relatively fixed, this kind of queue is called a fixed queue.
Dynamic queue: If the original queue members in the observation can continue to exit, new observation objects can join at any time, and the queue members are constantly changing, it is called a dynamic queue.
Features:
1. Belongs to the observation method
2. Establish a control group
3. From "cause" to "effect", the temporal sequence is from front to back.
4. Can confirm the causal link between exposure and outcome.
use:
1. Test the hypothesis of etiology
2. Describe the natural history of disease
3. Evaluate spontaneous preventive effects
type
Prospective cohort study: Study subjects are grouped according to their exposure status at the beginning of the study (current). At this time, the outcome of the study has not yet appeared, and it requires prospective observation for a period of time to obtain it. This design model is called an immediate or prospective cohort study.
Historical cohort study: Grouping of subjects based on historical data available to the researcher at the beginning of the study regarding the exposure of study subjects at a certain point in the past.
Bidirectional cohort study: also called a mixed cohort study, that is, after a historical cohort study, prospective observation is continued for a period of time. It is a design model that combines a prospective cohort study with a historical cohort study, so it has both The advantages of the above two categories make up for each other's shortcomings to a certain extent.
Selection of research subjects
Exposure group selection
Specially exposed groups; general population; organized groups
Selection of control group
1. Internal control: within a group of research subjects
2. External control: When occupational groups or specially exposed groups are used as the exposed group, a control group needs to be found outside the group.
3. Total population comparison: readily available morbidity or mortality statistics for the entire region
4. Multiple controls: Two or more control forms reduce the bias caused by using only one control and enhance the reliability of the results.
Statistical Inference: Calculation of Rates
1. Cumulative incidence rate: The research object is a fixed cohort, the population is relatively stable during the observation period, and the observation can be maintained for a long period of time.
Cumulative incidence rate = number of cases (or deaths) during the observation period/number of people in the cohort at the beginning of the observation period
2. Incidence density: usually suitable for dynamic cohorts. The follow-up time of cohort studies is relatively long, and it is difficult to require research subjects to remain still. The length of observation time varied among study subjects. At this time, it is obviously inappropriate to use the total number of people at the beginning of the observation as the denominator to calculate the incidence rate.
Incidence density = number of cases (or deaths) during the observation period/total number of person-hours during the observation period
(Number of observation hours = Number of observations x Observation time)
Relative risk
Relative risk (RR): It is the ratio of morbidity or mortality in the exposed group to the morbidity or mortality in the unexposed group.
RR=Ie/Io=(a/(a b))/(c/(c d))
The meaning of RR:
1. When RR=1, it means that the incidence probability of the exposed group is equal to that of the non-exposed group, and exposure has nothing to do with the disease;
2. When RR>1, it means that the incidence probability of the exposed group is greater than that of the non-exposed group, and exposure increases the risk of disease and may be a risk factor for the disease;
3. When RR<1, it means that the incidence probability of the exposed group is less than that of the non-exposed group. Exposure reduces the risk of disease and may be a protective factor for the disease.
Advantages and Disadvantages
advantage:
1. More suitable for common diseases
2. Deducing effects from causes with less bias
3. The incidence rates of the exposed group and the non-exposed group can be calculated, and the relative risk and specific risk between the two groups can be measured.
4. Multiple outcomes can be observed in one investigation.
5. Facilitate calculation of dose-response relationships
shortcoming:
1. Not applicable to rare diseases.
2. Observation is time-consuming, labor-intensive, and expensive.
3. The preparation work is relatively arduous, the scientific design requirements are high, and the implementation is difficult.
4. The workload of calculating exposed person-years is relatively heavy.
5. Only one factor or a group of factors can be studied at a time, so it is not suitable for diseases with multiple causes.
Wondershare EdrawMind
