Observational study
Observes individuals and measures variable of interest but doesn't attempt to influence the responses; do so to describe a group or situation
Experiments
Deliberately impose some treatment on individuals in order to observe responses; study whether the treatment causes a change in responses
Confounded/ lurking variables
Variables are of this variety when their effects on a response variable cannot be distinguished from each other
Treatment
any specific experimental condition applied to the subjects
Subjects
the individuals studied in an experiment
Factors
The explanatory variables in an experiment
Randomized comparative experiment
An experiment that uses both comparison of 2 or more treatments and random assignment of subjects to treatments
Simple experimental design
Subjects --> treatment --> measure response
Control group
The group in an experiment that doesn't receive the treatment
The principles of experimental design
1. Control the effects of lurking variables by comparing 2 or more treatments
2. Randomize by using chance to assign subjects to treatments
3. Use enough subjects per group to reduce chance variation in results
Statistically significant
When an observed effect is so large that it would rarely occur by chance, the effect is...
Double-blind experiment
neither the subjects nor the people who interact with them know which treatment each subject is receiving; common example is medical experiments & placebo effect
Placebo
A dummy treatment; many patients respond even to these because they trust the doctor
Block
A group of individuals that are known before the experiment to be similar in some way that is expected to affect the responses to the treatments
Matched pairs design
Compares just 2 treatments by choosing pairs of subjects that are as closely matched as possible with each one of them randomly receiving each treatment. In other designs, one individual receives both treatments one after the other in a random order.
block design
the random assignment of individuals to treatments is carried out separately within each block