Elfazuh, a Martian, reads an Earthling study claiming that exercising helps people lose weight. However, participants in the study merely self-reported their weight. Elfazuh thinks weight wasn't actually measured because people may have been lying. What is Elfazuh's concern about the study?
1) The study did not provide any evidence to support the claim
2) The study relied on self-reported weight, which may not be accurate
3) The study did not have a control group for comparison
4) The study did not consider other factors that could affect weight loss