The type of the studies

on

Goal

  • Telling;
  • analytic study vs descriptive study
  • experimental study vs observational study.

Summary

  • If comparison group exist, it is analytic study, not descriptive study.
  • If the comparison group is assigned by researcher forcefully, it is experimental study, not observational study.
  • All experimental study is analytic study, and all descriptive study is observational study


1. Analytic study vs Descriptive study

Descriptive Studies: It is like a personal journal.These studies are designed to describe the distribution of variables within a population, without looking at relationships between variables. They can answer questions such as "What is the incidence or prevalence of a disease in a population?" or "What demographic groups are most affected by a particular condition?" Examples of descriptive studies include case reports, case series, cross-sectional studies, and surveillance studies. These studies often provide initial insights that can then be explored further in analytic studies.

For example, a study documenting the rate of acupuncture usage in a population over a given time period would be a descriptive study. It's merely describing the prevalence of a particular behavior (acupuncture usage) without comparing it to any outcome or other groups.

Analytic Studies: These studies go further and examine associations between different variables, often focusing on the relationship between an exposure and an outcome. They test specific hypotheses about these relationships, seeking to determine whether there's a correlation or causal link between the variables. They always include a comparison (control) group.

Analytic studies can be either observational (such as cohort, case-control, and cross-sectional studies) or experimental (such as randomized controlled trials). The key feature of an analytic study is the presence of a comparison group, which allows researchers to observe differences between groups and link these differences to the exposure. For example, a study that compares the blood pressure levels of people who practice Tai Chi to those who don't practice Tai Chi (while controlling for other factors) would be an analytic study. The two groups (Tai Chi practitioners and non-practitioners) serve as comparison groups for each other. If the study finds a statistically significant difference in blood pressure levels between the groups, it could suggest an association between Tai Chi practice and blood pressure levels. But, comparing before and after acupuncture is not analytic study, because of absence of comparison group. It is simple description of what happened with acupuncture for blood pressure.

  • before and after comparison is NOT an analytic study
  • Treatment rate of acupuncture without comparison is NOT an analytic study
  • comparison(analysis) of groups in survey data IS (observational analytic study)
An analytic study compares groups and explores the relationships between variables, aiming to understand correlations or even causality, whereas a descriptive study simply describes characteristics of a group or population without making these comparisons.

  • Analytic studies test hypotheses about exposure-outcome relationships (correlation or causality)
  • Descriptive studies just can build hypotheses about exposure-outcome relationships 

Key checkpoint: See if that study has comparison group regardless experiment or observation. If the study has any kind of control, it is analytic study. 



2. Experimental study vs Observational study

Experimental Studies: In an experimental study, the researchers actively manipulate one or more variables (the "experimental" or "intervention" variables) and then observe the effect of this manipulation on other variables (the "outcome" variables). The goal is to see if changing the experimental variable causes a change in the outcome variable. Experimental studies often include a control group that does not receive the experimental manipulation, allowing for comparison. These studies are often randomized and blinded to reduce bias.

For example, let's consider an experimental study on the effect of acupuncture on migraines. Researchers might recruit a group of individuals who suffer from migraines and randomly assign them to two groups. One group receives acupuncture treatments (experimental group) while the other group receives a sham acupuncture treatment or no treatment at all (control group). The researchers then compare the frequency and severity of migraines between the two groups after a certain period. If there's a significant difference in the outcome between the groups, it might suggest that the acupuncture treatment is effective in reducing migraines.

Observational Studies: In an observational study, the researchers do not manipulate any variables. Instead, they observe the subjects as they are and measure variables of interest. Observational studies can be descriptive (like case reports and cross-sectional studies) or analytic (like cohort and case-control studies).

For example, consider an observational study on the relationship between acupuncture and migraines. Here, researchers might identify a group of individuals who choose to undergo acupuncture treatment for migraines (exposed group) and a group of individuals who do not undergo acupuncture (unexposed group). The researchers then compare the frequency and severity of migraines between these two groups. If there's a significant difference, it might suggest a correlation between acupuncture and migraine relief.

The key distinguishing factor between experimental and observational studies is whether the researcher intervenes or manipulates the subjects of the study. In experimental studies, the researcher actively manipulates one or more variables, while in observational studies, the researcher merely observes the subjects as they are, without any intervention.


Review

Observational studies without control group (descriptive observational study)

  • case study
  • case series
  • prospective case series

Observational studies with control group (analytic observational study)

Nature determines who is exposed to the factor. It can claim association between groups

  • Cohort study
  • Case-control study

Experimental study with control group

    Researcher determines who is exposed to the factor. It can claim causation between groups

    • RCT

    Experimental(??) study without control group

    • Quasi-experiment study



    Next article

    https://acupunctureherbalmedicine.blogspot.com/2023/05/retrospective-and-prospective-study-and.html


    Type of the studies
    graph TB A["Does it have comparison group?"] -- "No" --> B["Descriptive Study"] A -- "Yes" --> C["Is the comparison group assigned by researcher's intervention?"] C -- "Yes" --> D["Experimental Study"] C -- "No" --> E["Cohort Study or Case-Control Study"]