Using administrative healthcare data to recruit study subjects: experience with 'camouflaged sampling'

To recruit a sample of asthmatics heterogeneous for short-acting (SA) beta-agonist use while protecting their privacy, and to compare participants recruited via 'camouflaged sampling' to those recruited through media advertising.

Direct and indirect patient contact using camouflaged sampling was used to recruit a stratified random sample of asthmatics, identified based on their receipt of a prescription for a SA beta-agonist. Volunteers were recruited through media advertising. Recruitment rates were determined for both indirect and direct patient contact, and sampled participants were compared to volunteers recruited through media advertising for differences in SA beta-agonist use, demographic socioeconomic factors, and pulmonary function.

109 and 93 participants were recruited through camouflaged sampling and media advertising, respectively. Direct and indirect patient contact resulted in recruitment rates of 5 and 9%, respectively. Sampled participants were more heterogeneous for SA beta-agonist use, older, more likely to smoke or receive social assistance, and of lower socioeconomic status (SES) than volunteers. There was no difference in the association between SES and the magnitude of SA beta-agonist use between recruiting methods.

Although recruitment rates were lower than anticipated, camouflaged sampling facilitated stratified sampling of a targeted population and resulted in a more heterogeneous sample while protecting patient privacy.