Dr. Shatner wants to determine if after Covid, first-year college students still have trouble adjusting to living on campus. Students will create collages in their University Seminar courses of their first month at school. They will then send digital copies of the collages to their friends and loved ones at home. Dr. Shatner thinks this will help students feel like their two separate lives are merging together, which should decrease feelings of homesickness. they will recruit 100 new students to Texas State. Dr. Shatner will measure how homesick the students feel after the first week living on campus. After 4 weeks on campus, the students will make their collages in University Seminar. Then one month later, Dr. Shatner will measure how homesick they feel again. When Dr. Shatner runs the study, they find that students felt less homesick at the second measurement compared to the first. They conclude making collages in University Seminar is an effective way to help students adjust to campus life.

1. Given Dr. Shatner's research design, what are two threats to their study's internal validity?

2. What is a comparison group? Why would adding the comparison group help decrease the threats to internal validity?

3. Imagine in Dr. Shatner's study that only 90 of the original participants completed the measure of homesickness the second time (10 participants had left the university and were unavailable). What threat to internal validity is this?