2.1. Randomization Procedure through an Online Survey

With the combined popularity of the internet and the use of electronic devices, online surveys have become more effective and easier to operate, thus making their use a trend in health studies [40]. Traditionally, the RRT was conducted under a face-to-face interview so that physical devices such as cards, a coin, or dice could be used to generate randomized outcomes to determine whether the individual would answer the sensitive question or the unrelated question. Some scholars, such as Holbrook and Krosnick [41], have commented that using physical devices to generate randomization can be problematic because respondents may think the process is cumbersome and that might make them ignore the randomization procedure or drop out of the survey. Hence, using a physical randomization device, especially in an online survey, is not desirable. Online electronic devices such as a digital spinner [42] or an electronic coin toss [43] have been introduced in online surveys with RRT questions. In Peeters’s study [42], respondents were asked to answer either the sensitive question or the unrelated question solely based on the random outcomes of the digital spinner results generated by the computer (e.g., if the digital spinner stopped on an imprinted area, the person had to answer the sensitive question. If the spinner stopped on an empty area, the person was to answer the unrelated question). In Coutts and Jann [43], respondents were asked to answer either the sensitive question or the unrelated question solely on the basis of the random outcomes of the computer’s electronic coin tosses (e.g., if the electronic coin resulted in “head,” the respondent had to answer the sensitive question; if it was “tail,” the person was to answer the non-sensitive question). However, a shortcoming of using solely an online electronic device to execute the randomization procedure is that respondents may think the researcher is cheating by displaying a nonrandom outcome in which the researcher must surely know the true response from the respondent to the sensitive question. This discourages the respondents from giving honest answers.

To avoid that concern, our randomization procedure included an extra step that asked the respondents to select a private number in addition to the random outcome generated by the computer, and to answer the sensitive question only if the random number matched the respondent’s privately selected number. Under that procedure, the researcher had no opportunity to cheat by controlling the device and displaying a non-random number since he or she had no idea which number would be displayed nor which number the respondent had chosen. This procedure with the extra step increased the trustworthiness of our randomization device compared with that of Peeters [42] and that of Coutts and Jann [43]. An example of the randomization procedure we adopted is illustrated in Figure 2.

An example of this study’s randomization procedure.