UCLA

Consenting visitors to a health survey Web site were randomly assigned to a "matrix" presentation or an "expanded" presentation of survey response options. Among 4,208 visitors to the site over 3 months, 1,615 (38 percent) participated by giving consent and completing the survey. During a pre-trial period, when consent was not required, 914 of 1,667 visitors (55 percent) participated (odds ratio 1.9, P<0.0001). Mean response times were 5.07 minutes for the matrix format and 5.22 minutes for the expanded format (P=0.16). Neither health status scores nor alpha reliability coefficients were substantially influenced by the survey format, but health status scores varied with age and gender as expected from U.S. population norms. In conclusion, presenting response options in a matrix format may not substantially speed survey completion. This study demonstrates a method for rapidly evaluating interface design alternatives using anonymous Web volunteers who have provided informed consent.