Background
Methods
Search strategy
Selection criteria
Data extraction
Assessment of risk of bias
Level of evidence | Study type | N of studies | Reference |
---|---|---|---|
Good | Randomised controlled trial (RCT) | 9 | |
Fair | Non-RCT comparison of strategies or groups | 14 | |
Poor | Descriptive study (with quantitative data, e.g., % of target group recruited, often single strategy pre-post)# | 48 | |
Poor | Qualitative study (e.g., focus groups or interviews) | 16 | |
Poor | Case studies without data | 28 |
Results
Group | N of studies | References* |
---|---|---|
Ethnic/racial groups (e.g. Latino, Hispanics, Asian, or mixed) | 40 | |
African American | 19 | |
Substance abusers | 14 | |
General - ‘vulnerable’, ‘minority’, ‘disadvantaged’ | 11 | |
Indigenous people | 8 | |
Low income, disadvantaged area | 7 | |
HIV (alone or with drug addiction or ethnic) | 7 | |
Low income rural | 7 | |
Gay, lesbian, bisexual and transgender (GLBT) | 4 | |
Low literacy group | 4 | |
Homeless people | 4 | |
High risk Youth | 3 | |
Survivors of violence | 3 | |
Sex workers | 1 | [122] |
Mental illness | 1 | [40] |
People with a disability | 1 | [116] |
Author & Year | Type of review | Target group/s | Barrier/s addressed | Strategies reviewed | Main results & conclusions |
---|---|---|---|---|---|
Sampling | |||||
Marpsat & Razafindratsima [152] | Narrative with 60 included studies | General ‘hard-to-reach’ | No sampling frame – difficulties sampling hidden groups and rare populations | 1. Time-location sampling. | Each non-probability sampling method described advantages and disadvantages of each strategy presented with no preferences recommended. |
2. Respondent driven sampling. | |||||
3. Capture-recapture (or contact-re-contact). | |||||
Malekinejad et al. [151] | Systematic review with quantitative analysis with 123 included studies from Africa, Asia, Europe, Latin America, Oceania | HIV related (injecting drug users, sex workers and homosexual men) | Sampling for HIV surveillance studies | Respondent drive sampling | All but 13 studies reached >90% of their intended sample size and only six failed to reach equilibrium for key demographics suggesting representativeness. The majority of studies used formative research, face-to-face interview formats, three referrals per participant, a single interview site for data collection, and incentives. |
Aldana & Quintero [153] | Narrative review with 18 included studies | General ‘hard-to-reach’ | Sampling for surveillance studies | 1. Venue-based time-location sampling. | Advantages and disadvantages of each strategy discussed. |
2. Targeted sampling. | Targeted sampling which requires ethnographic data provides important qualitative information. | ||||
3. Respondent driven sampling | Venue-based sampling allowed a systematic recruitment of participants and produced probability samples but only of the visits to the venues included in the sample. | ||||
Respondent driven sampling based on social networks permitted calculation of population estimates. | |||||
Atkinson & Flint [150] | Narrative review with 22 included studies | General ‘hard-to-reach’ | Sampling in general | Snowball sampling | Described advantages and disadvantages of snowball sampling with no comparison with other methods. Recommended particularly for qualitative research. |
Peterson et al. [34] | Narrative review with 32 studies | Illicit drug users | Sampling following discharge from treatment | Targeted sampling (i.e., non-probability sampling method requiring identification of high yield locations). | Comparison with ‘in treatment’ samples suggested representative samples obtained using targeted sampling. |
Faugier & Sargeant [154] | Narrative review with about 30 studies (number not reported, estimated from reference list) | Sex workers, HIV, substance abuse populations | Sampling issues | Non-random methods of sampling such as snowball sampling. | Snowball sampling, although not probability or random sampling, has been used for research with hard to reach groups. |
Andresen et al. [138] | Narrative review with about 100 studies (number not reported, estimated from reference list) | ‘Low-frequency’ populations in public health surveillance surveys | Sampling groups with small numbers in the population results in small samples of hard to reach groups in population surveys | Improving analysis using: | Discussed advantages and weaknesses of each strategy for increasing small-group participation in population surveys. Recommendations included: |
• Aggregating data – by location or time | Partnering with agencies (e.g., state hospital associations); | ||||
• Spatial smoothing | Bilingual interviewers; | ||||
• Small area estimation | Including non-random sampling methods to enhance samples; | ||||
• Exact statistics | Changes in statistical methods. | ||||
• Provider profiling methods | |||||
Using non-probability sampling strategies: | |||||
• Convenience sampling | |||||
• Snowball methods | |||||
• Publicly available or commercial lists | |||||
Improving recruitment methods: | |||||
• Extending survey modes (to include face to face) | |||||
• Staff training | |||||
• Incentives | |||||
• Involve community members | |||||
• Bilingual interviewers and surveys | |||||
Data collection methods: | |||||
• Use qualitative methods and participatory research | |||||
• Multi-method surveys | |||||
Kalton [149] | Narrative and selective review with about 90 studies (number not reported, estimated from reference list) | Rare (low prevalence) populations | Sampling | Over-sampling | Options discussed include: |
• Disproportionate stratified sampling; | |||||
• Two-phase sampling; | |||||
• Use of multiple frames; | |||||
• Multiplicity sampling; | |||||
• Location sampling; | |||||
• Panel surveys; | |||||
• Use of multi-purpose surveys. | |||||
Recommended use of more than one sampling method and tailoring based on study research question. | |||||
Recruitment
| |||||
Dhalla & Poole, [147] | Systematic review with 19 studies from OECD countries and 39 studies from non-OECD countries | Hard-to-reach participants for HIV vaccine trials | Low recruitment rates into HIV vaccine trials | Two types of participant motivation to participate in HIV vaccine trials: altruistic (social benefits) and personal benefits) | Motivators which may help develop and tailor recruitment strategies included: (altruistic) to protect partner/community/others; help stop spread of AIDS; help research; help find cure; (personal) protection from HIV; because friends are; to enjoy sex; monetary and non-cash incentives; doctor/military suggestion; personal recognition; free health care. |
Swanson & Ward [131] | Systematic review with qualitative synthesis with 107 studies (about 50% were on the barriers to recruitment only) | American ethnic minorities | Recruitment into clinical trials | Effective and ineffective methods outlined | ‘Effective’ methods for recruitment based on methodologically superior studies included: |
• Community partnerships | |||||
• Community leaders | |||||
• Community involvement in development | |||||
• Formative qualitative research | |||||
• Gifts and incentives | |||||
• Provide transport | |||||
• Community advisors | |||||
• Sustainable interventions | |||||
• Grants to health services | |||||
• Establish networks of doctors | |||||
• Cultural/family tailoring | |||||
• Recruitment materials in target language | |||||
• Tracking databases | |||||
• Active recruitment with research staff to help completion of forms | |||||
• Train staff in cultural issues | |||||
• Employ community residents as part of research | |||||
UyBico et al. [141] | Systematic review with quantitative analysis and consideration of studies’ methodological quality with 20 included studies | Vulnerable populations | Recruitment into intervention health research | 1. Social marketing (e.g. mass mailing, telephone calls, mass media). | Successful strategies included: |
2. Community outreach (via churches, community organisations, presentations/meetings, community events, door to door canvassing). | • Social marketing was successful in 44% of studies. | ||||
3. Through health system (doctor referral, health centre recruitment, registry, patient records) | • Health system based strategies were successful in 40% of studies. | ||||
4. Referrals (by friends/family, other research participants) | • Referrals strategies were successful in 35% of studies. | ||||
• Community outreach was successful in 13% of studies | |||||
Lai et al. [142] | Systematic review with qualitative synthesis with 14 included studies | Under-represented populations | Recruitment into cancer clinical trials | 1. Recruitment letters/flyers and telephone calls. | Only three studies reported efficacious strategies: |
2. Incentives and gifts. | • Media campaign (compared to clinic registry recruitment) | ||||
3. Recruitment facilitators (doctors, insurers, businessmen and community organisations). | • Enhanced mailing process, church project sessions conducted by African Americans, letters and telephone reminders (compared to mailed survey only and telephone only) | ||||
• Companies providing researchers with names and phone numbers (compared with employees actively signing up at work) | |||||
Howerton et al. [143] | Systematic review with 18 studies | Under-represented populations (recruitment to cancer clinical trial) | Clinician characteristics, attitudes and practices | 11 clinician level promoters of recruitment | Clinician factors such as communication style, lack of trust of research, lack of awareness, logistics and cost are barriers to the recruitment of under-represented populations in cancer clinical trials. Addressing those barriers through incentives (e.g., extra staff), provider training, institutional affiliation, helps improve attitudes and recruitment. |
Wendler et al. [146] | Systematic review with 20 studies with meta-analysis | Racial and ethics minorities | Participants’ willingness to participate and attitudes towards research | Changing attitudes to research versus other pragmatic barriers to research. | No differences in willingness (as measured by consent rates of racial minority groups versus non-minority Whites) to participate in research by racial group. Attitudes towards research were positive. Efforts should focus on improving access to research not changing participant attitudes. |
Systematic and thematic review with about 38 studies (number not reported estimated from reference list) | Ethnic minority groups | Participant fear and mistrust, inappropriate exclusion criteria and study designs, costs to researchers, lack of ethnic staff, socio-cultural issues, cultural myths | N/A – review of barriers only | Under-representation caused by a combination of factors that need to be addressed. Potential strategies are discussed, but not included in the review (such as strategies to reduce fear and mistrust, education and training, community links and advocacy, outreach strategies, recruitment through primary health care) to address barriers. | |
Ford et al. [132] | Systematic review with 46 studies | Racial and ethnic minorities, older, rural and low socioeconomic status | Mistrust of research, perceived harms, costs, transport, lack of education, time, fear, family, provider attitudes and characteristics, communication, lack of protocols, religious/spiritual beliefs, low health literacy, culture | N/A – review of barriers only | Concluded under-represented groups face numerous barriers to participation in cancer-related trials. |
Guiliano et al. [144] | Non-systematic narrative review | ‘Minority’ groups | Structural, cultural and linguistic factors limiting participation in cancer research | N/A- review of barriers | Research where participants feel ownership, trust and receive results more likely to increase participation. |
Miranda et al. [145] | Narrative review with about 48 studies (number not reported, estimated from reference list) | Low income Latinos | Lack of insurance, time, child care, and transport. Cultural barriers and beliefs in traditional non-medical healers. | 1. Use of health services for recruitment. | Research needs to be culturally sensitive and to remove logistic barriers. Bilingual and bicultural staff should be part of the research team. |
2. Bilingual and bicultural staff. | |||||
3. Developing culturally sensitive research materials. | |||||
Flory et al. [140] | Systematic review with 30 included studies | Low literacy | Participants limited understanding and literacy | 1. Multi-media, | Extended discussion (educator or staff spending more time talking one-on-one to participants) was the most effective strategy according to methodologically superior studies. |
2. Enhanced’ consent forms, | |||||
3. Extended discussions | |||||
4. Test/feedback (quizzing participants about the information) | |||||
5. Miscellaneous | |||||
Shavers-Hornaday et al. [139] | Non-systematic and narrative review with about 100 studies (number not reported, estimated from reference list) | African-Americans | Participant barriers (distrust, health care access and utilization, quality of care). | Outlined strategies based on 11 cancer trials that successfully recruited African/Americans | Effective recruitment strategies based on the results of 11 cancer trials that successfully recruited representative samples of African American include: |
Investigator barriers (low recruitment and retention, cost, relationships with minority health professionals)/ | • An active commitment to recruiting African American subjects; | ||||
• Community outreach programs and advertisements; | |||||
• Involvement of local churches and community organizations; | |||||
• Publicity campaigns directed at African Americans; | |||||
• Participant logistics such as convenient testing times, transport, convenient location; | |||||
• Use of incentives; | |||||
• Use of African American role models; | |||||
• Flexibility and willingness to change protocol | |||||
• Use of lay health workers; | |||||
• Door to door canvassing | |||||
Ndumele et al. [156] | Systematic review with 45 included studies | Minority populations with chronic disease | Recruitment into qualitative research | 1. Health care setting | Based on 21 studies that provided data-based results: no discernible patterns of recruitment method that seemed associated with greater rates of participant recruitment. |
2. Community organisations | |||||
3. Electronic or mailed invitations | |||||
4. Media | |||||
5. Word of mouth | |||||
6. Incentives | |||||
7. Recruits from existing databases | |||||
Data collection & measurement
| |||||
Hergenrather et al. [133] | Systematic review with qualitative synthesis with 31 included studies | Various vulnerable populations | Engaging communities and collecting data in acceptable methods | Photovoice (i.e., use of photographs to encourage group discussion). | Photovoice expanded representation and diversity of community members participating in health research. |
Halcomb et al. [134] | Integrative review with about 40 studies (number not reported, estimated from reference list) | Culturally and linguistically diverse (CALD) | Challenges in focus group research with CALD populations | 1. Involvement of key members of the target group; | Involvement of leader members of the target group; bilingual facilitators; consider particular CALD group as not all are the same are key considerations. |
2. Logistical convenience; | |||||
3. Physical environment should be considered; | |||||
4. Bilingual facilitators; | |||||
5. Consider particular CALD group as not all are the same (e.g., incentives not acceptable to some). | |||||
Intervention participation and fidelity
| |||||
Sheridan et al. [130] | Systematic review with 38 included articles | Low health literacy populations | Populations with low health literacy and language difficulties | Design features of health information interventions. | Multiple strategies are required to improve availability of health information and intervention for low literacy/numeracy groups. Design features found to improve participant comprehension: |
• Presenting essential information first or on its own; | |||||
• Presenting disease risk or treatment benefit information using the same denominators | |||||
• Presenting numerical information in tables not text | |||||
• Adding icon arrays to numerical information | |||||
• Adding video to verbal narrative | |||||
Glazier et al. [157] | Systematic review with 17 included studies | Socially disadvantaged groups | Diabetes care interventions for socially disadvantaged groups | Patient, provider and health system interventions for diabetes | Positive intervention features were: |
• Cultural tailoring | |||||
• Community or lay educators | |||||
• One-on-one interventions | |||||
• Behaviour related tasks | |||||
• Feedback | |||||
• High intensity and long duration | |||||
Negative intervention features were: | |||||
• Didactic teaching | |||||
• Focus on increasing (diabetes) knowledge | |||||
Across stages of research
| |||||
Yancey et al. [148] | Systematic review with qualitative synthesis and consideration of studies’ methodological quality with 95 included studies | African American and American ethnic groups | Recruitment and retention in general | 1. Community involvement in research. | Based on methodologically superior studies, strategies recommended to increase recruitment and retention include: |
2. Incentives and logistical aids (e.g., transport). | |||||
3. Cultural tailoring. | |||||
• Population based sampling strategies are unlikely to produce sufficient numbers | |||||
• Personal contact and mass media were efficacious for recruitment | |||||
• Non-restrictive eligibility criteria | |||||
• Community involvement more critical to retention than recruitment | |||||
• Timely incentive payments | |||||
• Cultural tailoring | |||||
Johnson et al. [155] | Systematic review with 6 included studies (RCTs only) | African American | Recruitment and retention into genetic and genomic studies | 1. Population strategies (phone, mail or postcard); | • Phone recruitment (63%-91%) significantly better than mail or postcard (3%-19%). |
2. community-based strategies (community engagement and partnerships); | • Community engagement produced mixed recruitment results (1% - 82%) with locals as recruiters important success factor. | ||||
3. Incentives | • Only 1 trial of incentives found no effect on retention. | ||||
Wallace & Bartlett [158] | Narrative review with about 38 studies (number not reported, estimated from reference list) | African American and Hispanic girls and women | Recruitment and retention | Recruitment: | Recommended using all of the strategies outlined. |
• Building trust | |||||
• Familiarity and visibility | |||||
• Racial and ethnic concordance | |||||
• Convenience | |||||
Retention: | |||||
• Provide transport | |||||
• Language, literacy and culturally appropriate, | |||||
• Emphasising safety | |||||
• Flexibility | |||||
• Incentives | |||||
• Regular communication | |||||
• Veracity | |||||
Grove et al. [135] | Narrative review with 20 studies | Indigenous Australians | Recruitment and retention in longitudinal research | Community participation (and ownership), developing relationships. | Three studies reported successful recruitment and retention using community participation strategies. |
Booth et al. [136] | Non-systematic (selective) narrative review with about 13 studies (number not reported, estimated from reference list) | Homeless people | Sampling and data collection, ethical and fieldwork issues | Key recommendations were: | |
1. Convenience (non-random) sampling. | • Use common sense to enhance practicality and reduce burden on participants; | ||||
2. Building trust. | • Cultural sensitivity; | ||||
3. Simple consent materials. | • Take non-threatening approach; | ||||
4. Incentives to participate. | • Appropriate language; | ||||
5. Cultural sensitivity. | • ‘Hanging out’ with target group; | ||||
6. Using a non-threatening approach. | • Provide feedback; | ||||
7. Providing feedback. | • Note style of clothing; | ||||
• Use informants and service providers; | |||||
• Incentives | |||||
Mathers & Cramer [137] | Narrative review with about 28 studies (number not reported, estimated from reference list) | Gay, Lesbian, Bisexual, Transgender (GLBT) | Recruitment & data collection: difficulties identifying ‘hidden’ samples. Researchers as ‘outsiders’. Researcher verbal and non verbal cues influencing survey responses. | Web and videoconferencing | Web and videoconferencing are private and non-threatening for hidden populations and should provide more accurate data. |
Developing a sampling frame
Barriers
Barriers | Strategies |
---|---|
Difficult to locate or reach and access groups (e.g., homeless people living on the streets) | |
Frequent change of address or self-identifying, (e.g. GLBT) results in no sampling frame. | |
• Capture-recapture [95] | |
• Adaptive sampling [53] | |
Low prevalence in population (e.g., Aboriginal people). | |
• Statistical analysis techniques to population survey data for low-frequency samples [91] | |
• Internet samples [51] |
Strategies to improve sampling
Non-probability sampling
Sampling through community organisations
Combinations of sampling strategies
Comparisons of strategies
Other strategies
Recruitment and gaining consent
Barriers
Barriers | Strategies |
---|---|
Lack of trust in research/research team or uncertainty regarding how survey results will be used | |
Fear of authority | |
Perceived harms of research | |
Mistreatment and exploitation | • Use of ‘hand-written’ envelopes (vs. printed) [106]* |
No benefits for participation (i.e., ‘fly in, fly out’ research) | • Enlisting community leaders (60, 113,114,115,127]. |
• Emphasising potential benefits [74]. | |
• Improved communication and culturally relevant education materials [32]. | |
Lack of education/awareness re research or health promotion/low health literacy, difficulties understanding consent and what the study is about | |
Cultural beliefs, gender roles/age related issues | |
Gatekeepers (therefore patients/community are not aware of research): doctors or nurses who do not approach minority participants, high turnover of staff limits relationships | |
Doctor poor communication methods | |
Rigid exclusive eligibility criteria | • Patient education materials [32]. |
Stigma/fear of exposure | |
Low response rates in general | |
• Text messaging [65]. | |
• Two stage recruitment 1) to a low commitment survey then 2) to the trial [83]. | |
• Shorter surveys [106]. | |
• Develop a registry with interested people [25]. |
Improving response rates
Community-research partnerships
Use of media and social marketing
Strategies to encourage gatekeeper support
Comparison studies
Other strategies
Data collection and measurement
Barriers
Barriers | Strategies |
---|---|
Language or literacy problems | |
• Short surveys [106]. | |
Lack of landline telephone (for population based telephone surveys) or highly mobile population | • Mailed survey instead of telephone [90]*. |
Mistrust of researchers and the use of the data | |
Improving data collection and measurement methods
Inclusive language and methods
Flexible data collection methods
Use of technology to gather data
Pilot testing measures
Comparison studies
Intervention delivery and uptake
Barriers
Barriers | Strategies |
---|---|
Concerns regarding: Randomisation, i.e., not getting treatment Loss of control (re: allocation) Mistrust | |
• Use trusted sources of information (e.g. doctor or family) [87]. | |
• Participant education regarding the benefits of randomisation [73]. | |
Health intervention not culturally appropriate (with community values and beliefs) | |
Distance for delivery of intervention (rural groups) | • Group-delivered (one-on-one) telephone intervention [88]. |
Negative framing of health information, emphasis on disparities | • Positive and progress emphasised in health information [37]*. |
Improving intervention participation and fidelity
Alternative methodologies and study designs
Community/participant involvement in intervention design
Comparison studies
Other
Attrition and retention
Barriers
Improving retention rates
Incentives and gifts
Multiple tracking, reminders and contact procedures
Altruism and benefits of research
Building relationships and trust
Comparison studies
Multiple strategies
Barriers | Strategies |
---|---|
Difficulty maintaining contact; highly mobile populations; frequently changing contact numbers | |
Practical barriers such as transport difficulties, lack of child care, lack of leave from work | |
Forgetting to return for follow-up | • Use of study logos on gifts [74]. |
• Phone text message reminders [65]. | |