Efficacy of Exercise in Reducing Depressive Symptoms

1. Efficacy of Exercise in Reducing Depressive Symptoms

2. Brief Details • They wanted to see if exercise has an effect on one’s level of depression. • Hypothesis: Exercise will result in a greater decrease in depression scores in individuals with at least one l allele • Independent variable: exercise • Dependent variable: depression score

3. Methods • Participants • Recruited from undergrad kinesiology class • Both women and men, 18-23 years old • Around 130 participants involved • Randomly assigned to either exercise intervention group or no treatment control group using random numbers table • 171 participants were assessed before intervention • 129 completed the intervention phase (64 in control group & 65 in exercise group)

4. Methods • Procedure • Participants were given a health history questionnaire • To be able to participate the students had to be physically able to exercise (determined by the questionnaire) • Participants were excluded if they were currently being treated for a psychiatric condition • Students took a pre-test and post-test that was comprised of the Beck Depression Inventory, Life Experiences Survey, and Multidimensional Scale of Perceived Social Support • Divided into two groups: Exercise intervention group and no treatment group • Exercise group was required to attend 3 exercise sessions per week for 5 weeks • Each session the participant had to do 30 minutes of cycling on a stationary bike at 60-70% of maximum heart rate

5. Methods • Results • 2 groups did not differ significantly in depression scores at pretest • At post-test the exercise group showed a significant reduction in depression score compared to the no-treatment control group • The post-test scores for social support were not significantly different from pre-test scores • Therefore the decrease in depression in exercise group was not a result of social interaction

6. External Validity • Results of the study: The group that performed the exercise had significant reduction in depression scores compared to the control group • To what places/settings/people/times are they generalizing: The researchers state that these results are specific to individuals with at least one l allelle. They also state that individuals with the sshomozygotes. Basically, the researchers recognize these results are very specific to a certain genotype group- the lallelle group- NO GENERALIZATION

7. External Validity • Questioning the Conclusions of the study: The conclusion of the study is weakened by a few different things including: • SAMPLE SIZE- which is too large • DISTRIBUTION OF PARTICIPANTS INTO TREATMENT GROUPS- different genotypes(specifically the ll and ls genotypes) were put into one group when they should have ideally been in two separate groups • The ss genotype had relatively low pretest depression scores making their low post test depression scores insignificant • HOWEVER, the researchers acknowledge these limitations of their results and point out that further study is needed

8. Construct Validity • Constructs: Exercise and Depression Scores • Specifically, what is being measured: The impact of exercise on depression scores • Constructs defined:For exercise: 3 exercise sessions a week consisting of 30 minutes of cycling on a stationary bike- Has Face validity, because cycling is indeed a good form of exercise. However, using it as the only form of exercise may be too broad a definition of exercise- MONO-OPERATION BIAS- should use multiple forms such as running, swimming, etc.; For Depression Scores: A Pre-test and Post Test that consists of 3 different tests intended to measure depression- The Beck Depression Inventory, the Life Experiences Survey and the Multidimensional Scale of Perceived Social Support

9. Construct Validity • Constructs defined cont.: Depression Scores: Has definite face and criterion validity- The tests used were a good measure of depression. Also shows content validity because the tests used to measure depression are well known, and used by many professionals in the field of study • Restricted generalizability across constructs and levels: Some participants could have been injured during the exercise program which would interact with their effort and therefore their outcome- if they aren’t putting forth much effort they aren’t exercising to the effect of getting their heart rate high enough to experience the release of the hormones that can lower depression allegedly

10. External Validity • The researchers claim that exercise causes a decrease in depression scores. • This is a multiple group design with random assignment. The two groups were given both a pre and post-test. • This study displays temporal precedence because the exercise comes before the decrease in depression. • When there is no exercise, there is no decrease in depression, which gives this study covariation.

11. External Validity • Social Interaction Threats: • Diffusion or Imitation; the group which had no treatment (exercise) may have decided to work out on their own. • Resentful Demoralization; individuals in the control group may feel resentful towards the treatment group. These individuals may fall into a deeper depression due to no exercise.

12. External Validity • Key Internal Validity • The causal inference is reasonable in this study, due to the researchers taking the right steps to avoid single and multi-group threats by having a control group and using random assignment.