In this study, we explored the existence of volunteer or consent bias by using 2 different methods to solicit the participation of school personnel in research evaluating competency in the use of an epinephrine auto-injector (EpiPen®): partial disclosure and full disclosure. The participation rate was higher in the partial disclosure group (between group difference 18.7%, 95% CI, 13.3%-24.1%) and participants from the full disclosure group were more likely to earn a perfect score (between group difference 10.5%, 95% CI, 1.8%-19.2%), demonstrate the 3 critical steps correctly (between group difference 20.3%, 95% CI, 10.0%-30.6%), and identify signs of anaphylaxis (between group difference 16.2%, 95% CI, 6.2%-26.2%). These results suggest the existence of a volunteer or consent bias, a form of selection bias where individuals who volunteer for a study may have specific characteristics that distinguish them from non-volunteers and that may affect outcomes; for example, participants may be more likely to find the topic interesting and usually expect to be evaluated positively . In our study, school personnel from the partial disclosure group were not given all the information about the purpose of the study and the EpiPen® assessment prior to the assessors’ visit. Consequently, they were unlikely to be reluctant to participate because of concerns regarding their knowledge and competence, but their performance was generally poorer. In contrast, those in the full disclosure group were completely aware of the purpose of the assessment and those with a greater interest and possibly knowledge in the topic were more willing to participate, leading to an overestimation of competence relative to the general population. It is also possible that those who chose to participate also practised or prepared prior to the evaluation, enhancing their performance. This suggests that the timing and the process of informed consent can affect the participation rate and the interpretation of the results. Although this threat to the validity of a study that arises from the consent process has been described previously [20, 21, 28, 29], we are the first to explore its influence in allergy research.
In comparing the 2 approaches, we tried to ensure that the school boards were as similar as possible other than in the detailing of the consent by randomly selecting school boards of similar size in the same urban area. In addition, in Quebec, as school nurses responsible for school personnel training are employed by the Ministry of Health and Social Services and not by individual school boards, the EpiPen® training is less likely to be influenced by school board environments and likely to be reasonably similar throughout the province. Further, we adjusted for possible differences between the partial and full disclosure groups through regression analyses and demonstrated that the full disclosure group continued to perform more favourably. However, it is possible that the school boards differed in ways we did not consider or were unable to measure and these differences influenced the performance of school personnel. It should be noted that in the multivariate analysis, prior training with an auto-injector and being in the full disclosure group were independent predictors of a perfect score. Hence, although fewer in the full disclosure group reported training than those in the partial disclosure group, they still performed better and we anticipate that had more in the full disclosure group reported training, the between group difference in performance would be even greater.
It is also possible that there was contamination within and between groups. As it was not feasible to conduct all school assessments on the same day, assessments were staggered over an 8-month period. Hence, it is possible that school personnel within the partial or full disclosure group assessed early in the process communicated with those in the partial disclosure group who were assessed later, informing them of the purpose of the assessment. Such contamination would likely minimize our between group difference and make our assessment of selection bias conservative. In addition, our analyses were adjusted to take into account the grouping of participants by school, and we found that the effects of within-school versus between-school variations were not significant, as the size of the confidence intervals was only minimally affected. Although it was not the purpose of this small study, it would have been interesting to compare participants and non-participants in terms of their anaphylaxis interest and knowledge to better characterize the bias illustrated in this study.
Our results reporting that only 26.3% (95% CI, 19.6%-33.9%) among the full disclosure group are able to accurately demonstrate the use of the EpiPen® are disturbing as they likely overestimate the competence of school personnel. The 15.8% (95% CI, 10.8%-21.8%) demonstrating correct usage in the partial disclosure group is likely more representative, but it, too, is probably an overestimate as the most informed were still more likely to participate even in this group. Although personnel in elementary schools performed more favourably, possibly because they feel younger children are more reliant on them, only 23.7% (95% CI, 18.7%-29.4%) were able to correctly use the EpiPen®. These results are worrisome because it has been shown that inability to use an epinephrine auto-injector may contribute to a delay in the treatment of anaphylaxis [11, 30] which can increase the risk for fatality [10, 12].
Given the poor performance observed despite 89.2% of all participants reporting training, the quality and frequency of school personnel training needs to be examined. In Quebec, school personnel are trained in allergy and anaphylaxis management and EpiPen® use on a regular basis . However, the content and frequency of training programs may vary as there are no provincial guidelines. In our study, training involving an EpiPen® demonstrator was associated with better performance. Other authors have also recommended use of the auto-injector training device and frequent review to increase knowledge retention [11, 15]. A training model using an audio-visual presentation and written material on anaphylaxis and epinephrine administration followed by a meeting with allergic children was developed for school personnel in San Francisco in 2004, and significantly increased knowledge and perceived self-efficacy in 53 participants . Such a training model could be adapted and studied in Canada.