Kelly is examining how an LGBTQ+ peer support group affects members' self-concept. She uses a randomized, pretest-posttest design to compare changes in self-concept over time between those in the treatment and control groups. The treatment intervention consists of 10 weekly group meetings that discuss social issues faced by those in the LGBTQ+ community. Six weeks into the study, she notices that 25% of the participants in the treatment group have stopped attending the group meetings. What threat to validity should Kelly be most concerned with?

Possible answers:

Attrition

Testing

Unreliability of Treatment Implementation

Reactivity to the Experimental Situation