1.4.3  Independent and Paired Samples
1.4.3  Independent and Paired SamplesIn both observational and experimental studies, we often want to compare two or more groups. When comparing two or more groups, cases may be independent or paired.
 Independent Groups
 Cases in each group are unrelated to one another.
 Paired Groups

Cases in each group are meaningfully matched with one another; also known as dependent samples or matched pairs
Example: Exam Scores
An instructor wants to compare students' scores on the midterm and final exam. This is most often done by obtaining a sample of students and recording each student's midterm exam score and final exam score. In other words, there would be two measurements for each student. This is an example of a matched pairs design because data would be paired by student.
Example: Shoes
A shoe company is studying how many shoes Italian men and women own. In one research study they take a random sample of 500 Italian adults and ask each individual if they identify as a man or women and how many pairs of shoes they own. The men and women in this study are in two independent groups.
In a second study the researchers use a different design. This time they take a random sample of 250 heterosexual married couples in Italy (i.e., 250 husbands and 250 wives). They record the number of shoes owned by each husband and each wife. This is an example of a matched pairs design. Data are paired by couple.