Simulating a control pool to economize control recruitment in a matched case-control study

Control recruitment in case-control studies is problematic if no register for the study base exists. If random telephone contact is used and study base members comprise a relatively small proportion of the population then control recruitment can be resource-intensive. In a matched case-control study with prospective case recruitment, the study base is accessed repeatedly for control recruitment and in this context we propose a dynamic pool to economize control recruitment. The pool gets added to when a study base member is contacted but doesn't match the current case. The pool is then accessed for future cases before resorting to random telephone contact again. Using Stata, we simulate the operation of a control pool to quantify the possible economies under a range of likely scenarios. These simulation results are compared with early experience in the Farm Injury Risk among Males study, which found modest efficiency gains (4 controls recruited from the pool at a saving of approximately 90 telephone contacts per control).