The second technique for examining the relationship between two variables
involves comparing two or more groups of scores. In this situation, one of the
variables is used to differentiate the groups. For example, one group of students
is selected from high-income families and a second group is selected
from low-income families. The second variable, each student’s grade average,
is then measured to obtain a score for each individual. An example of the
resulting data is shown in Table 6.1. Note that the researcher compares the scores for the high-income group with the scores for the low-income group. A
systematic difference between the two groups of scores provides evidence of a
relationship between family income and academic performance.
There are three different research strategies that examine relationships
between variables using the kind of data shown in Table 6.1. The differences
among the three strategies are based on the questions that they address and
their ability to produce unambiguous answers.