A team of psychologists have developed an experimental treatment program for a learning disorder with the expectation that the treatment would enable recipients to score higher than before on a test of learning ability. To test the treatment, they randomly select a pool of 30 volunteers who have been diagnosed with the disorder and who have volunteered for the treatment program. Following treatment, the participants are retested on the learning ability test and their scores compared to earlier scores

I believe this is a dependent sample test since we are retesting the same group.

1. Describe a potentially confounding variable and how that might affect the conclusions from the study.