This prospective cohort study incorporated a standardized recruitment protocol, embedded with two small randomized controlled trials of participant contact strategies, to evaluate methods and predictors of time to contact with participants for enrollment into an extended duration longitudinal study. In the two small randomized trials, we could not detect any significant difference between “personal” versus “business” formats of the envelope used for a standard recruitment letter, nor between phone messages using the study name versus the principal investigator’s name. Among 34 potential predictors examined in this study, only two were independently associated with time to contact with participants. Having the participant’s last visit conducted outside of the research clinic due to patient illness/condition, and not having a self-reported history of chronic fatigue were each independently associated with a longer time to contact.
In our study, the overall rate of contact with participants by the end of the 12-week standardized recruitment protocol was relatively high at 72% (of whom 95% provided informed consent), compared to the 6 - 60% rates experienced in other trials of recruitment strategies (8
). We attribute this relatively high rate of contact to our repeated contact attempts and the use of different methods to contact patients. However, participant contact rates, within a 1-month time frame, to each of the general recruitment letter and the mail trial were low (16% and 6% respectively). We observed a relatively higher contact rate with the phone versus mail strategies. The low response rates to our two letters may be explained, in part, by 44% of participants still undergoing their 12- or 24-month follow-up visits at the time of the letter (i.e. they may not have responded simply because they had not yet reached the end of the original study period in order to be eligible for enrollment in the extended follow-up study). However, the relatively high prevalence of chronic illness and/or drug or alcohol use in our population also may have played a role in the low rate of participant response to the letters.
To our knowledge, only a single study has evaluated factors predicting the time to participant response. Tennant el al
. studied factors associated with the time to response to a postal questionnaire (5
) and found that participants who were physically dependent responded sooner. Other research in this field has studied factors associated with subjects consenting to participate in research (with no investigation of the time required to contact subjects and obtain consent). Predictors of consent and its timing were not specifically evaluated in our study for two reasons: (1) not all participants were required to consent at the time that we contacted them (i.e. those still under-going 12- and 24-month follow-up would not require consent for up to 24 months later), and (2) based on experience with our cohort, we believed that the greatest barrier to participation was successfully contacting participants, rather than their reluctance to provide informed consent, as demonstrated by the very high consent rate obtained among all participants who were successfully contacted. Nonetheless, there are a number of potentially relevant studies within this larger body of literature to discuss. For example, Janzon et al.
found that patient illness was negatively associated with participation (11
) similar to the finding in our evaluation of time to contact with participants. However, our other predictor of time to contact (i.e. a history of patient-reported fatigue) has not been specifically investigated in prior research, but was considered within our analysis based on the high prevalence of this symptom among ALI/ARDS survivors (24
While other studies have found either positive or negative associations of socioeconomic and health-related factors, such as age, sex, race, educational level, employment status, current health status, immobility, and alcohol addiction or other psychiatric history, with participation in research (4
), we found no association of any of these variables with our time to contact with participants. Moreover, although missing a prior follow-up visit was negatively associated with participation in prior research (10
), this factor was not associated with time to contact in our study. Conflicting results within this literature and with our study findings may be due to the different end point studied in our research, or differences in the target participant populations evaluated in each study. Findings may not be readily generalizable outside of the specific participant population.
Regarding our finding that patients with a chronic fatigue history had a shorter time to contact, we speculate that this result may be due to chronically fatigued participants more frequently being at home to receive a phone call or more frequently having assistance at home that may help with phone-based responsiveness. However, these hypotheses need further evaluation to confirm their association with the time to contact of participants.
There are several potential limitations of our study. First, our study was focused on time to contact with members of an existing research cohort for participation in an extended follow-up protocol, which may limit the generalizability of our findings. However, the circumstances of our study (i.e., needing to recruit patients from within an existing cohort) are not unusual in clinical research (21
); therefore, the findings from this study still have importance and relevance. Second, our study had a limited sample size and a relatively low response rate to the two randomized trials making the trials likely under-powered to detect an important effect of the interventions evaluated. This low response rate was not anticipated when designing the trials and our available sample size was constrained to those subjects already participating and eligible for the extended duration study. Further randomized trials investigating the effect of different participant contact strategies are needed. Third, some of the predictors evaluated in this study were measured at the participant’s immediately preceding research visit. These predictors may have changed since that time resulting in a misclassification error. However, this potential misclassification is likely infrequent given the relative stability of these medical-related factors in this patient population and the relatively short median time (7 months) between participants’ last visit and our contact with them. Lastly, we focused on the time to participant contact, rather than the rate of contact or recruitment/informed consent because we believed it was the key underlying factor in achieving participation in our cohort and because some participants were still undergoing 12- and 24-month follow-up visits, making consent for the extended follow-up protocol a less relevant end point. Since most studies have a time-sensitive nature for patient contact and recruitment, understanding the time to participant contact and the factors affecting it are important for designing contact strategies.