Cross-sectional studies

Cross-sectional studies have several names, including cross-sectional studies, surveys, and Prevalence study, Epidemiological study.

Epidemiologic study

In this type of study, a researcher investigates the presence of a disease in a short time and simultaneously examines certain factors that are probably related to the disease. Therefore, this type of research is non-directional since the exposure factor and disease are examined simultaneously. In terms of timing, this type of research is considered a concurrent study.

It is worth mentioning that these studies take place at a given time not at a period of time.

These studies only deal with the relationship between the agent and the illness and the causal relationship between them cannot be verified because the confounding variables in the studied groups are not controlled. Moreover, it is hard to distinguish the exposure and the risk factor.

This type of study is the first step to verify a causal relationship between a particular outcome and a particular exposure.

Case-control study

Case-control studies are retrospective studies. This means that case-control groups are categorized based on the disease or the outcomes. In the next step, the history of each control group is searched to determine if the risk factors are effective. The important point is the selection criteria of the case and control groups, as well as the confounding effects should be similar. In cases where the confounding factors are out of the researcher’s control, samples should be matched based on the following methods:

Paired matching: There should be one or more similar case-controls for the investigated case. To clarify, for a 16-year-old boy, there should be a control case with the same age and gender.

Frequency matching: In this method, the confounding factors should be compared and matched in two groups, not the samples. For instance, in order to match 15 participants with the age range of 18 years in a group, there should be another group with a similar age range and distribution of gender.

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