Question 19: An investigator is evaluating the effect of tea tree oil on the eradication of toenail fungus in a randomized controlled trial. The outcome of toenail fungus will be ascertained by clinician examination. However, the investigator is concerned that clinicians may more favorably rate improvement for participants they know had the tea tree oil treatment (information bias).

Which design-level strategy could the investigator use to decrease this type of information bias? (Choose the best answer)

A. Increasing study power.

B. Increasing the sample size of the treatment and placebo group.

C. Blinding of study personnel (including examining clinicians to treatment assignment).

D. Use of a cross-over design.

E. Stratified randomization according to age categories.