Definition of Epidemiology
Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of the knowledge acquired to control disease in that population or geographical area.
Epidemiology definition is not just a definition but a philosophy
If suppose car seller uses this philosophy, he will look for the distribution and determinants, which increase the sales of car units, this is exactly what business analytics try to do to get more leads and increased sales of their products or services.
What do you mean by study in epidemiological study design?
In simple words, it is a scientific procedure involving answering questions using population data.
Now the way you collect data to increase or decrease the credibility of your answers. Now the way we collect data or information is termed as STUDY DESIGN more appropriately.
Ecological study and case-series
An ecological study is done on groups of people but lacks a comparison, so the latter in which specific people with the same exposure or disease are studied to describe something unusual.
as the human mind understands better when comparison or context has been put, so evolved the comparison studies.
Case-control and Cohort study
As we move from simple observations to comparative or analytic study, collected data becomes more valuable as in a case-control study we can calculate the odds ratio and tell the risk involved with the exposure in question. The same is true for cohort studies where we calculate the Risk ratio. A cohort study overcomes the limitation of a case-control study which is temporal association. (Whether the chicken first or egg!)
Randomised Control Trial (RCT): An interventional Epidemiological study
As analytical studies like cohort and case control are not free of bias and error people have found a way to balance it in both the group by randomized control trial (RCT) where study participants are randomly allocated to each group, and neither participants nor investigators know what intervention they are receiving known as double blinding.
Randomization is the heart of RCT, but we can only randomize people for intervention which is having benefits reported from initial observations, and never something potentially harmful to them.
Systematic review and Metanalysis: Summarize all the relevant studies done using RCT
Where systematic review synthesizes, analyzes, interprets, and summarises the findings, meta-analysis tries to combine all the statistical analysis done on similar studies.
Hierarchy of Epidemiological Studies
The hierarchy of study design exists because of our quest to find the most robust evidence which improves the quality of human life by reducing disease-related morbidity and mortality.