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

BACKGROUND AND OBJECTIVE: To evaluate the value of balanced incomplete block designs in quality improvement research, and their capacity to control for the Hawthorne effect. METHODS: 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). RESULTS: 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. CONCLUSION: 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.