A researcher wants to assess the effect of sleep on test per

A researcher wants to assess the effect of sleep on test performance. She brings students into the lab, gives each student an IQ test, and then asks them how much they slept last night. Is this an experiment? Why/why not?

Solution

Recall the definitions of these terms:

An observational study measures the characteristics of a population by studying individuals in a sample, but does not attempt to manipulate or influence the variables of interest.

A designed experiment applies a treatment to individuals (referred to as experimental units orsubjects) and attempts to isolate the effects of the treatment on a response variable.

Now, since last night\'s sleep and IQ level are both unchanged , and are simply being observed, this is an observational study, not an experiment.