Barriers and facilitators for recruiting and retaining male participants into longitudinal health research: a systematic review | BMC Medical Research Methodology

The database searching and the forward and backward citation checking yielded 16,457 and 13 papers respectively (16,470 total). 6,108 duplicates were removed resulting in 10,362 articles available for screening (Fig. 1). Of these, 9,214 studies did not meet the inclusion criteria based on titles and abstract screening and resulted in 1,148 full-text studies selected for further screening (Fig. 1). A total of 1,124 studies were then excluded with 255 having no male specific data, 166 conference abstracts, 115 HIV related research, 106 cancer related research, 78 studies had no included data on barriers or facilitators, 71 studies with a focus on males > 60 years, 69 studies from racial or ethnic minority, 52 studies were unrelated to health recruitment and retention, 48 Alzheimer’s or dementia research, 39 related to illegal drugs, 29 papers were studies with less than 3 study visits, 24 papers were males < 16 years of age, 22 systematic review/review papers, 19 focused on socioeconomically disadvantaged populations, 14 uncompleted studies/study protocol, 13studies were < 12 weeks duration, and 4 fathers in early childhood interventions (Fig. 1).

PRISMA diagram depicts the search, screening, eligibility and inclusion results

A total of 24 articles remained and the data was extracted and included in this review. The oldest of these studies was published from 1976 [36] and the most recent, 2023 [37, 38]. All of the included studies were conducted in Western countries except Cheraghi et al., which was based in the Middle East [39] and Schilling et al., which was based in India [37]; two were located in United Kingdom [40, 41], two in France [42, 43], one in Finland [44], one in Sweden [45], one in The Netherlands [46], one study across combined European nations [29], one in Germany [47] ten in North America [36, 48,49,50,51,52,53,54,55,56] and three in Australia [38, 57, 58] and are described in Table 1. Participant characteristics varied with study focus including participants with specific health conditions, such as overweight [41, 57], having an occupational injury [40, 41], having visited a sexually transmitted infection clinic [46], or being treated for a psychological disorder [44, 50, 53], COVID related issues [37, 54], or habits such as alcohol abuse and smoking [56]. Some studies recruited participants from specific subgroups, including veterans [36], workers of an electricity company [42] and people that had attended a spouse abuse abatement program [50]. All twenty-four studies met the inclusion criteria for age. One of the studies was a family cohort study that recruited families of children with cystic fibrosis and congenital heart disease and required participation of both parents [51].

Of the included studies, 20 had male and female participants [37,38,39,40, 42,43,44,45,46,47,48,49, 51,52,53,54,55,56,57,58], with a number of these studies having a predominantly male sample [42, 52, 53, 58]. Four studies recruited only male participants [36, 41, 50, 61] (Table 2). The included studies with mixed sex either described male and female characteristics separately or clearly stated that there were no significant differences in recruitment and retention based on sex. All included studies used a minimum of three study visits or data collection, and the maximum number of study visits or data collections was 95 visits [41] and one study had up to 300 interactions with participants [44]. The minimum study length of included studies was 16 weeks [50] and the maximum study duration was 43 years [45]. All included studies collected demographic data [36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58, 61].

Recruitment

Overall, all studies provided information on recruitment rates and 19 provided information on retention rates [36, 38,39,40,41, 43,44,45,46,47, 49,50,51,52, 55,56,57,58, 61] (Table 2). A variety of methods for male participant recruitment included advertising [36, 43, 54, 57], letters of invitation [39,40,41,42,43, 47, 52, 56,57,58, 61], selection of participants from larger cohorts [42, 43, 50, 53], or recruitment from hospitals or registers [37, 44, 48, 51, 54, 57] (Table 3). The most common method was sending letters of invitation, used in 11 out of the 24 studies, and yielded recruitment rates between 4.4% and 79.3% [47, 52]. Irvine et al., recruited participants through letter of invitation and time space sampling, and reported that time space sampling was difficult, time consuming and only yielded one participant per 11 field visits [23]. Snow et al., used multiple methods for recruitment, including recruitment from work sites and public sites, mass mailing, telephone, media, and referral methods and reported that mass mailing was the best method of these [55]. Rose et al., attributed their high recruitment rates to advertising and therefore people that agreed to participate had done so voluntarily and were more likely to be interested in the study and health interventions in general [36]. To maximise male participation, vanWees et al., adapted their recruitment methods to target male participants by raising awareness and a greater sense of responsibility in terms of male health through flyers or personalised invitations [46].

Barriers

A variety of factors were identified that interfered with male participation in longitudinal research are shown in Table 4. Some of these were situational and included participant death or relocation [36, 39, 42, 45, 48, 51, 53, 55, 57, 61]. While other barriers included time commitment [40, 58], reluctance for medical testing [58], or the belief that the study is an invasion of privacy [58]. A large number of studies reported that men did not attend study visits [40, 58], were not interested in the study or could not be bothered to participate [36, 40, 41, 44, 48, 49, 51, 58, 61], and study staff received no response to invitations [40, 41, 61].

Facilitators

Many studies employed a variety of strategies to increase participation for males (Table 5). These varied from offering free medical screening [36], reminders for appointments [40, 42, 46, 48, 51, 52, 56,57,58, 61], or enrolment of wives [36] or family members [39, 51] to assist in retention. Several studies used a range of strategies, particularly [43, 56, 57], with varying degrees of success.