1. Avoiding Attrition Bias
Estimating Expected Dropout Rates in Yoga Therapy Research
Dr. Holger Cramer
Department of Internal and Integrative Medicine, University of Duisburg-Essen, Essen, Germany
ARCCIM, University of Technology Sydney, Australia

2. Designing a Yoga Therapy RCT

3. Adequate Sample Size for a Yoga RCT?
At least 100 patients?
At least 100 patients per study arm?
At least one more patient than the last study?
Enough patients to be able to detect the expected effect size with adequate power!

4. Sample Size Calculation
Conventions:
α ≤ 0.05
Power ≥ 0.80
Effect size?

5. Sample Size Calculation
Conventions:
α ≤ 0.05
Power ≥ 0.80
Effect size?

6. Sample Size Calculation
Conventions:
α ≤ 0.05
Power ≥ 0.80
Effect size?

7. Sample Size Calculation
Conventions:
α ≤ 0.05
Power ≥ 0.80
Effect size?

8. Sample Size Calculation
Conventions:
α ≤ 0.05
Power ≥ 0.80
Effect size: depends on the research question

9. Sample Size Calculation

10. Sample Size Calculation
Conventions:
α ≤ 0.05
Power ≥ 0.80
Effect size: depends on the research question
Drop-out rate?

11. Sample Size Calculation
Conventions:
α ≤ 0.05
Power ≥ 0.80
Effect size: depends on the research question
Drop-out rate?

12. Drop-Out Rates
Underestimation: Loss of power (false negative results). Overestimation: Unnecessary large numbers of participants might be exposed to a potentially ineffective or even dangerous intervention; enhanced study expenses.

13. Drop-Out Rates: Example

14. Drop-Out Rates: Example
20.4%

15. Drop-Out Rates: Meta-Analysis

16. Drop-Out Rates: Meta-Analysis*

17. Drop-Out Rates: Country of Origin

18. Drop-Out Rates: Medical Condition

19. Drop-Out Rates: Medical Condition

20. Drop-Out Rates: Medical Condition

21. Drop-Out Rates: Gender

22. Drop-Out Rates: Age

23. Drop-Out Rates: Intervention Content

24. Drop-Out Rates: Intervention Duration

25. Avoiding Attrition Bias
Dropout rates in yoga therapy RCTs usually can be expected to not exceed 15 to 20%.
Yet dropout rates beyond 40% are possible depending on the participants’ sociodemographic and health condition.

26. Avoiding Attrition Bias: Example
Yoga vs. usual care for adults of both gender with low back pain.
12-week intervention including asanas, pranayama and meditation.
Required sample size n=94.

27. Avoiding Attrition Bias: Example
Yoga (12.73%) vs. usual care (14.72%) for adults (13.06%) of both genders (12.59%) with low back pain (10.55%).
12-week intervention (12.94%) including asanas (13.46%), pranayama (13.33%) and meditation (14.60%).
 Estimated 15% drop-out rate should be adequate (total sample size n=111).

28. Avoiding Attrition Bias
Cramer H, Haller H, Dobos G, Lauche R. A systematic review and meta-analysis estimating the expected drop-out rates in randomized controlled trials on yoga interventions. Evid Based Complement Alternat Med. 2016;2016:

29. Thanks a lot for your attention!