Armand Conducts a Study for His Research Method Class

Armand conducts a study for his research method class.He is curious as to whether watching romantic movies makes people more committed to their romantic relationship.He collects a sample of men in dating relationships and divides them into two groups.One group watches a 5-minute clip of a movie in which the main characters are having a romantic first date.The second group watches a 5-minute clip from the same movie in which the main characters break up.After the participants watch the movie clip,they are then asked to write a sentence about their relationship.Armand counts the number of uses of the words we and us as a measure of commitment.After conducting the study,he finds that there is not a statistically significant difference between his two groups.

-Armand's professor suggests that the null effect may be due to a large amount of within-group variance.State three causes of within-group variance in Armand's study.