4.2 - Observational Studies and Experiments
What is control?
Keep as many other variables as possible the same for all groups. Control helps avoid confounding and reduces the variation in responses, making it easier to decide whether a treatment is effective.
What is a retrospective observational study?
One that looks backwards for a duration of time.
What is a prospective observational study?
One that watches for outcomes during a study period.
What is an observational study?
One which observes individuals and measures variables of interest but does not attempt to influence the responses.
Does a retrospective or prospective observational study have fewer sources of bias and confounding variables?
Prospective.
What is a placebo?
A fake treatment given to a control group to prevent the placebo effect from being a confounding variable.
What are levels?
A specific combination of each of the factors in an experiment studying the joint effect of several studies.
What is the treatment?
A specific condition applied to the individuals in an experiment consisting of combinations of values of the explanatory variables (aka factors)
What is an experiment?
A study that deliberately imposes some treatment on individuals to measure their responses.
What is the difference between an explanatory variable and a response variable?
An explanatory variable is the variable that changes to cause a change in another (the response variable).
What is confounding?
Bias that occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other.
What are the 4 basic principles of experimental design?
Comparison, random assignment, control, and replication.
What are factors?
Explanatory variables in an experiment.
What does it mean for two variables to have an association?
If the values of one variable relate to or are correlated with the other.
What is replication?
Impose each treatment on enough experimental units so that the effects of the treatments can be distinguished from chance differences between the groups.
What is the primary benefit of using an experiment rather than an observational study?
One experiments can establish cause and effect (observational studies are more prone to confounding variables and bias).
What is the placebo effect?
The effect of a person's belief in a placebo drug or treatment on the result of the study.
What is an experimental unit/subject?
The smallest collection of individuals to which treatments are applied. Subjects are when the units are human beings.
What is comparison?
Use a design that compares 2 or more treatments.
What is random assignment?
Use chance to assign experimental units to treatments. This helps create roughly equivalent groups before treatments are imposed.