DOE_MSc

Researchers observe the effect of a risk factor (diagnostic test, treatment, or other intervention) without trying to change it. That means they just record what they see. There are two types of observational studies:

a) Cohort Study: For research purposes, a cohort is any group of people who are linked in some way. For instance, a birth cohort includes all people born within a given time frame. Researchers compare what happens to members of the cohort that have been exposed to a particular variable to what happens to the other members who have not been exposed.

b) Case control study: Here researchers identify people with an existing health problem (“cases”) and a similar group without the problem (“controls”) and then compare them with respect to an exposure(s).

-> Problem: They run the risk of containing confounding biases!

Confounding (“Verwirrung”) means that a factor (confounder) that is not directly investigated is associated with both the independent variable and the dependent variable and accordingly causes the relationship between the two variables (Spurious Correlation = “falsche Korrelation”)

Example: The fewer storks nest in an area, the lower human birth rate in the area

• direct relationship is most unlikely
• explainable trough urbanization (confounder)
• Urbanization leads to a decline in the stork population because more land is being developed
• Urbanization also leads to a lower birth rate because women tend to be more educated

Solution: Randomization

These studies are the solution to the disadvantages of observational studies. Experimental studies are ones where researchers introduce an intervention and study the effects. The Randomized double blind placebo control study/trial (= RCT) is considered the “gold standard” for producing reliable evidence because little is left to chance.

Aim: Treatment/exposures is planned, and its effects are investigated

Eligible people are randomly assigned to one of two or more groups. This ensures the comparability of the groups at study begin. Aim of randomization:

• Elimination of selection bias: is an experimental error that occurs when the participant pool is not representative of the target population. (parents with higher incomes >> more informed >> get their child vaccinated >> proportion would be larger in the treatment group)
• Elimination of confounding: Confounding means that a factor (=confounder), that it not directly investigated, relates to both the independent and dependent variable. This confounder then causes the relationship between the two variables (= Spurious Correlation) and not the treatment itself.
• Ensuring the comparability of the groups at study initiation (baseline data)

Blinding is a suitable technique to avoid distortion (“Verzerrung”) due to knowledge. Blinding eliminates conscious and unconscious influences on the treatment results. Also it ensures the comparability of the groups during / in the course of the study trough the similar treatment of the two groups and the independent evaluation of the effect of the exposure. There are several stages of blinding (cumulative):

• Open: no blinding
• Single-blind: Tested person has no knowledge of group membership.
• Double-blind: The person carrying out the experiment has no knowledge of the group membership.
• Triple-blind: Person doing the analysis has no knowledge about the group membership.

In Short:

Effect and aim of blindness.

• Elimination of conscious and unconscious influences of the treatment result (Placebo)
• Ensuring comparability regarding treatment of groups during the study
• Ensuring comparability on the final evaluation of both groups

Descriptive study

Descriptive character, suitable for forming hypotheses but insufficient for testing them.

Cross sectional study

Sample with variables of interest are collected and described at a specific time “Quality of Life of master’s students.”

-> Survey is typical

Correlational study

Same as cross sectional, but variables are correlated:

“Relationship between the time that master’s students spend studying on their own and their general quality of life”

dentification and quantification of effects of relationship, not fully suitable for hypothesis testing.

Case control study                                                     

Examines how cases and controls differ from having been exposed previously Looking back at the exposition (retrospective)

Example with Pädos (Vergangenheit wird angeschaut, wieso wurden sie so?)

Cohort study

Cohort = group of people with comparable initial conditions

One group is exposed to an influencing factor afterwards the groups are compared