Block design allowed for control of the Hawthorne effect in a randomized controlled trial of test ordering

To evaluate the value of balanced incomplete block designs in quality improvement research, and their capacity to control for the Hawthorne effect.

General practitioners teams were randomized into three arms and received an intervention on test ordering, relating to tests for two groups of clinical problems (A tests and B tests). In the two trials within the block design, we tried to control for the Hawthorne effect by comparing the complete intervention in both arms on either the A (arm I) or B tests (arm II); the arms acted as blind controls for each other. In the classical trial, the complete intervention on B tests (arm II) was compared with a control arm without any intervention on B tests (arm III).

The trials with the block design yielded statistically significant changes in the numbers of A tests ordered (P=.013), but not in the numbers of B tests ordered (P=.29). In the classical design, the complete intervention reached a marginally significant change in the B tests (P=.068). The Hawthorne effect was the same for both arms of the block design. In the classical design, the effect could to some extent be attributed to the Hawthorne effect.

Our block design allowed us to control for the Hawthorne effect. Suitable use of block designs may further our knowledge of nonspecific effects in quality improvement research.