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Triple-Blind Studies

A triple-blind study is one in which participants, researchers, and analysts are unaware of whether the participant received the treatment or the placebo in a random assignment trial. Although a double-blind design leaves only the participants and researchers unaware of the treatment assignment, a triple-blind study additionally keeps the team analyzing the data from knowing which group’s data—placebo or treatment—it is evaluating. This design allows objectivity in the data collection phase and in the data analysis phase—analysts are able to evaluate data without any bias.

Application

Barbara Henker and colleagues compared double- and triple-blind designs to examine a medication for hyperactivity in boys. They randomly assigned boys to one of two groups: the treatment group, which received the medication, and the placebo group, which received a placebo. They also used blind and nonblind raters/analysts. Results showed positive effects of the treatment, meaning the boys who received the medication displayed a significantly larger change in behavior than the boys in the placebo group. The double-blind design allowed the researchers to conclude that the medication itself was effective, as participants’ ignorance to their assignment ruled out any behavior that could be attributed to knowledge of receiving the medication.

The results of Henker and colleagues’ study also indicated that there was no difference in ratings between the double-blind raters and the triple-blind raters. Using a triple-blind design gave legitimacy to the results of the double-blind raters. The conclusions drawn from the double-blind design remained because even raters uninformed of group identity evaluated significant differences in behavior change between the treatment and placebo groups. A research team could also use this design to explore the legitimacy of school interventions for children with various learning disabilities.

Implications

Blinding in a study is important for its credibility, and each level of blinding adds more objectivity. Single blinding allows the researchers to make assumptions about the effect of a treatment without possible bias from the participants’ knowledge of their treatment status. Double-blind studies prevent any bias in the researchers’ behavior, causing confounding effects in the participants. Finally, triple-blind studies provide an even higher level of objectivity. They keep the participants’ treatment status unknown all the way through to the data analysis phase. Triple-blind studies add a degree of credibility to a study that is not often achieved with other designs.

See also Double-Blind Design; Experimental Designs; Placebo Effect; Random Assignment

Samantha B. Goldstein Marc H. Bornstein
http://dx.doi.org/10.4135/9781506326139.n713
10.4135/9781506326139.n713

Further Readings

Friedman, L. M., Furberg, C. D., & DeMets, D. L. (2010). Blindness. In L. M. Friedman, C. D. Furberg, & D. L. DeMets (Eds.), Fundamentals of clinical trials (pp. 119–132). New York, NY: Springer.
Henker, B., Whalen, C. K., & Collins, B. E. (1979). Double-blind and triple-blind assessments of medication and placebo responses in hyperactive children. Journal of Abnormal Child Psychology, 7(1), 1–13.
Pocock, S. J. (1983). Clinical trials: A practical approach. Chichester, UK: Wiley.
Schulz, K. F., & Grimes, D. A. (2002). Blinding in randomized trials: Hiding who got what. Lancet, 359(9307), 696–700.
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