Question

A widely publicized psychology experiment (Schnall, Benton & Harvey (2008)) suggested that handwashing reduced the severity of moral judgments. However, since the experiment was performed on a small sample, researchers at Michigan State wished to replicate the experiment with more participants. 132 participants (students at Michigan State) were individually shown a distasteful scene involving heroin addicts from the movie Trainspotting. 63 of the students, randomly selected, were instructed to wash their hands afterward; the remaining 69 students were not. All 132 students then had six different scenarios described to them. For instance, the "plane" scenario was as follows:

"Your plane has crashed in the Himalayas. The only survivors are yourself, another man, and a young boy. The three of you travel for days, battling extreme cold and wind. Your only chance at survival is to find your way to small a village on the other side of the mountain, several days away. The boy has a broken leg and cannot move very quickly. His chances of surviving the journey are essentially zero. Without food, you and the other man will probably die as well. The other man suggests that you sacrifice the boy and eat his remains over the next few days. How wrong is it to kill this boy so that you and the other man may survive your journey to safety?"

For each scenario, they were asked to make a moral judgment on a scale of 1 to 7, where 1 meant "Nothing wrong at all" and 7 meant "Extremely wrong." The purpose of the experiment was to determine whether handwashing caused the students' moral judgments to be less severe (i.e. smaller numbers.)

What are the experimental units in this study? What measurements are taken on each unit? How many independent samples are there?

Answer 1

Experimental units:

All 132 participants (the students of Michigan state) are the experimental units. Because each individual participant was treated separately and was asked to give the response. Thus, each individual participant is an experimental unit.

Measurements on each unit:

On each unit, the measurements taken are the scale of readings from 1 to 7 for making a moral judgement.

Independent samples:

There are 2 independent samples. They are:

1. The group of 63 students who had their hands washed.

2. The group of 69 students who did not have their hands washed.