Posts Tagged 'search strategies'

Hard-to-reach, hard to research

From a public health perspective, who are the hard-to-reach and how can we find research articles about them?

I was asked this question by a manager in the Winnipeg Regional Health Authority. He was looking for research specifically on immunization programs for the hard-to-reach as part of the WRHA’s ongoing preparation for the expected H1N1 epidemic. In order to assist my client, how was I to construct a search strategy in PubMed and other databases that would gather disparate materials together without a comprehensive catch-all subject heading?

Finding appropriate literature is just one of many challenges associated with conducting research on hard-to-reach populations. In the first place, how do we identify and sample certain groups of individuals for health research? Undoubtedly some populations are particularly vulnerable and difficult to contact. Other populations may be defined by characteristics such as ethnicity or sexual preference that are not recorded in routinely available data sources. Yet while the need for research on the hard-to-reach is pressing, a comprehensive definition of this population is lacking, and hence it is difficult to get one’s bearings.

Before creating my search strategy, I had to do some research of my own in order to get a handle on exactly the groups that I would be investigating.

Defining the hard-to-reach

What exactly is meant by ‘hard-to-reach’ is a matter of some debate. The term is inconsistently applied. It will sometimes be used to refer to minority groups, such as immigrants, LGBT people, or the homeless; it can be used to refer to ‘hidden populations’, groups of people who do not wish to be found or contacted, such as illegal drug users or gang members; at other times it may refer to broader segments of the population, such as the elderly, or young people, or people with disabilities. In the service context, hard-to-reach often refers to the underserved, certain minority groups, those slipping through the social safety net, and those who are deemed to be ‘service resistant’.

Yet another term used in this context is ‘hidden populations’, meaning those who are hidden from the point of view of research sampling. Hidden populations may also actively seek to conceal their group identity, as for example in the case of sniffers, injection drug users, LGBT people who are in the closet, sexually active teens, etc.

The hard-to-reach are also called the ‘seldom heard’. The use of this term indicates that these are people who do not have a collective voice and are often under-represented in consultation and involvement activities about developing services. ‘Hard-to-reach’ suggests that there is something that prevents their engagement with services. ‘Seldom heard’ emphasizes the responsibility of agencies to reach out to excluded people, ensuring that they have access to social care services and that their voices can be heard.

One of the chief difficulties in defining the hard-to-reach is the unintentional imputation of a homogeneity among distinct groups that does not necessarily exist. Or it may imply that the problem is one within the group itself and not within the approach. Attempts at categorization can have a stigmatizing effect. Hard-to-reach audiences have, with varying degrees of prejudice, been called obstinate, recalcitrant, chronically uninformed, disadvantaged, have-not, illiterate, dysfunctional, and information poor.

Associative and Nonassociative

In addition to these various ways to categorize the hard-to-reach, we can distinguish between ‘associative’ hard-to-reach populations, such as people at risk of AIDS, and ‘nonassociative’ hard-to-reach populations: those whose members do not normally have contact with other members.

Nonassociative populations share two primary characteristics. The first is demographic. There is no effective centralized information about them, and a large proportion of their members do not know each other. The second is that their members share characteristics or attributes that make it important for health and human services to have information about them to inform service planning, policy, and delivery. In addition to these features, they are often low-frequency populations, and they might be subject to stigma of various kinds.

There has been a large amount of research on associative hard-to-reach populations, those whose members are socially networked with each other and form a community (with literally thousands of studies being done on populations at risk of HIV and AIDS, such as injection drug users) – but there have been very few rigorous studies of nonassociative populations, particularly those that are less in the public eye, such as shut-ins.

The central focus of my search strategy was to gather together information precisely on these nonassociative populations. I was looking for groups defined by individual attributes (such as health or social status) where there is often no overriding reason for within-population socializing and where a substantial proportion of population members do not have strong social links with other members and, indeed, might even resist such contact. These hard-to-reach groups must be taken into account in immunization planning. No effective H1N1 prevention strategy can exclude them.

After much effort I decided to include the following in my search strategy:

  1. The homeless, the marginally housed, street people, and sex trade workers
  2. Shelter residents (including women and youth)
  3. Inmates in the correctional system (the incarcerated, parolees, the recently released, and those in half-way homes)
  4. Persons with serious and persistent mental health issues, including dementia or addiction
  5. Housebound persons (cystic fibrosis, arthritis), shut-ins, and the disabled
  6. The linguistically isolated (people with communication impairments, recent immigrants who are not fluent in English or French)
  7. Selected recipients of Family Services and Housing (employment income assistance, government housing, children in care)
  8. Miscellaneous nonassociative groups (transients, the uninsured, the socially isolated)

PubMed Search Strategy

Here, finally, is the strategy I employed for my PubMed search:

(“Immunization”[MAJR] OR vaccinat*[TI] OR immuniz*[TI] OR immunis*[TI] OR “Immunization Programs”[MAJR] OR “Immunization Schedule”[MAJR] OR “Influenza, Human/prevention and control”[MAJR] OR “unvaccinated population”)


(hard-to-reach OR “seldom heard” OR “hidden population” OR “hidden populations” OR homeless OR homelessness OR  “Homeless Persons”[MAJR] OR “Transients and Migrants”[MAJR] OR “Housing”[MAJR] OR “Prostitution”[MAJR] OR “sex trade workers” OR migrant OR vagrants OR “street worker” OR “street workers” OR “street people” OR “street youth” OR “street kids” OR “street children” OR “street involved” OR “unstable housing” OR shelters OR “shelter residents” OR (marginally[TIAB] AND housed[TIAB]) OR under-housed OR “marginalized population” OR “marginalized populations”

OR “Emigrants and Immigrants”[MAJR] OR “Refugees”[MAJR] OR “recent immigrants” OR “recent immigrant” OR “undocumented immigrant” OR “undocumented immigrants” OR “illegal immigrant” OR “illegal immigrants” OR emigres

OR “Vulnerable Populations”[MAJR] OR “Poverty”[MAJR] OR “Poverty Areas”[MH] OR “Social Class”[MH] OR “Socioeconomic Factors”[MH] OR “Urban Population”[MH] OR welfare OR underserved OR “underserved areas” OR “high-risk inner-city” OR socially-at-risk OR “at-risk population” OR “at-risk populations” OR slum OR slums OR ghetto OR ghettos OR favela OR favelas OR “low-socio-economic” OR disadvantaged OR low-income OR impoverished OR uninsured OR underinsured

OR “Prisoners”[MAJR] OR “Prisons”[MAJR] OR incarcerated OR incarceration OR “corrections facility” OR “correctional facilities” OR  “correctional population” OR prisoners OR probation OR probationers OR probationary OR parole OR parolees OR inmates OR “half-way house” OR “half-way houses”

OR “Drug Users”[MAJR] OR “Substance Abuse, Intravenous/psychology”[MAJR] OR “drug users” OR addicts OR addicted OR “drug addicts” OR “substance abuser” OR “substance abusers”

OR deaf[TIAB] OR “Hearing Impaired Persons”[MAJR] OR “Social Isolation”[MAJR] OR “low literacy” OR “language isolated” OR (linguistically[TIAB] AND isolated[TIAB]) OR homebound OR shut-in OR shut-ins OR “disabled persons”[MH]

OR “Mentally Ill Persons”[MAJR] OR “mentally ill”)


1. Brackertz N. Who is hard to reach and why? ISR working paper 2007. SISRQ/EL 06.07Institute for Social Research (Australia) [online]. Available from:

2. Southern DA, Lewis S, Maxwell CJ, Dunn JR, Noseworthy TW, Corbett G, Thomas K, Ghali WA. Sampling ‘hard-to-reach’ populations in health research: yield from a study targeting Americans living in Canada. BMC Med Res Methodol. 2008 Aug 18;8:57. PubMed PMID: 18710574

3. Stewart M, Makwarimba E, Barnfather A, Letourneau N, Neufeld A. Researching reducing health disparities: mixed-methods approaches. Soc Sci Med. 2008 Mar;66(6):1406-17. Epub 2008 Jan 14. PubMed PMID: 18248867.

4. Thompson S, Phillips D. Reaching and engaging hard-to-reach populations with a high proportion of nonassociative members. Qual Health Res. 2007 Nov;17(9):1292-303. PubMed PMID: 17968045.


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