2. Methods
REGRESSIONS, BROWN
A randomized, controlled trial design with two arms was used, as described previously [Participants were parents whose children were enrolled in a daycare facility, supplemented by adults recruited by the parents. The daycare was located in Grand Forks, North Dakota (ND), a city with one of the highest radon levels in the U.S. The average residential radon in Grand Forks is 11.7 pCi/L (433 Bq/mThe parents of children who attended the daycare facility received an invitation letter. The letter was placed in the children’s cubbies at the daycare and included a web address and QR code for the online, pre-exposure survey. Only one parent per family was eligible. To ensure adequate enrollment, parents could invite neighbors, friends, and/or co-workers to participate by sharing the link and QR code. Once a potential participant entered the web address or scanned the QR code, he/she was directed to the pre-exposure survey on Qualtrics. Upon accessing the survey, participants were asked to read the informed consent form. If participants proceeded with the online survey, it was considered that they had read the form and had agreed to participate.After participants answered questions measuring radon knowledge, radon testing attitudes, perceived severity and susceptibility, response efficacy, and self-efficacy, they were assigned to a condition. Participants randomized to the radon app received instructions on how to install the app and were instructed to use it for the next three months. App installation was verified by app activity data saved in a server maintained by the app developer. App users could request a free radon test at any time by using the app. They would receive a charcoal canister test, instructions for using it, and a pre-addressed, pre-paid envelope to use for returning the test to the lab. We used short-term (48–72 h) radon tests (Alpha Energy, Inc., Carrollton, TX, USA). These were bar-coded so that we could count the number of kits ordered and the number returned to the lab.Brochure condition participants received three EPA brochures during the ensuing three months via U.S. mail. These were: (1) Basic radon facts (All participants answered survey questions regarding demographic data (age, gender, race/ethnicity, housing type, household income, education level, and smoking status). Three months after participants completed the pre-exposure survey, they received an email with a web address for the post-exposure survey. A priori power analyses were performed using PASS (Power Analysis Sample Size Software. 2019, Kaysville, UT, USA) [Participants received $30 gift cards in exchange for participation in each of the pre-exposure and post-exposure surveys. Parents received a $25 gift card per additional participant they attracted, for a maximum of 3 per parent. This study was approved by the IRB at the University of North Dakota (IRB # IRB0004359) and was registered in ClinicalTrials.gov (ID: NCT05319457).The cognitive endpoints were similar to those we described previously [There were two behavioral outcomes: the rate at which participants ordered a free radon test kit and the rate at which they returned it to the testing lab. Both were measured via bar codes on the tests. To create radon knowledge index variables, a correct response was coded as “1” and an incorrect response, or “don’t know,” as “0.” We created two radon knowledge index variables for T1 and T2 whose sums reflect correct responses to 20 True–False radon knowledge statements. Two radon-testing attitudes variables were created by averaging five semantic differential scales in T1 and T2. These showed excellent reliability (Cronbach’s α in T1 = 0.95; Cronbach’s α in T2 = 0.90). Perceived severity variables were created using two Likert scales in T1 (Spearman–Brown coefficient = 0.91) and T2 (Spearman–Brown coefficient = 0.79). Perceived susceptibility, response efficacy, and self-efficacy variables were created similarly (Spearman–Brown coefficient for these variables were ≥0.80). The characteristics of participants in the two conditions were compared by Chi-Square. Changes in the cognitive variables were compared via paired t-tests. General linear models with repeated measures with interaction were used to detect differences in changes over time between the conditions. Differences in the proportion of participants in the two conditions who ordered a free radon test kit and those who returned it to the lab were compared using Z tests. Logistic regressions were used to test these differences while accounting for participant characteristics. Relative risks were estimated using stratified 2 × 2 tables.