Reproductive health services for refugees by refugees in Guinea I: family planning
© Howard et al; licensee BioMed Central Ltd. 2008
Received: 28 July 2008
Accepted: 16 October 2008
Published: 16 October 2008
Comprehensive studies of family planning (FP) in refugee camps are relatively uncommon. This paper examines gender and age differences in family planning knowledge, attitudes, and practices among Sierra Leonean and Liberian refugees living in Guinea.
In 1999, a cross-sectional survey was conducted of 889 reproductive-age men and women refugees from 48 camps served by the refugee-organised Reproductive Health Group (RHG). Sampling was multi-stage with data collected for socio-demographics, family planning, sexual health, and antenatal care. Statistics were calculated for selected indicators.
Women knew more about FP, although men's education reduced this difference. RHG facilitators were the primary source of reproductive health information for all respondents. However, more men then women obtained information from non-health sources, such as friends and media. Approval of FP was high, significantly higher in women than in men (90% vs. 70%). However, more than 40% reported not having discussed FP with their partner. Perceived service quality was an important determinant in choosing where to get contraceptives. Contraceptive use in the camps served by RHG was much higher than typical for either refugees' country of origin or the host country (17% vs. 3.9 and 4.1% respectively), but the risk of unwanted pregnancy remained considerable (69%).
This refugee self-help model appeared largely effective and could be considered for reproductive health needs in similar settings. Having any formal education appeared a major determinant of FP knowledge for men, while this was less noticeable for women. Thus, FP communication strategies for refugees should consider gender-specific messages and channels.
Reproductive health programming is never easy, but provision of effective care to populations affected by conflict and complex emergencies poses special challenges [1, 2]. The International Conference on Population and Development (Cairo, 1994) and the Fourth World Conference on Women (Beijing, 1995) marked a policy shift for both reproductive health and refugee health. The definition of reproductive health became more comprehensive, emphasising the reproductive health needs and rights of the underserved, particularly refugees and internally displaced persons (IDPs) [3–5]. However, despite strengthened international interest and policy frameworks, implementation remains difficult and quality research is minimal [2–4, 6–11]. Published studies have concentrated on refugees in more developed countries or stable camp settings.
Globally, refugees and IDPs number over 32.9 million , and "reproductive health needs do not disappear upon displacement" . Relief efforts have traditionally focused on acute-phase survival, including HIV prevention and basic emergency obstetric care . However, reproductive health spans relief and development and is essential for long-term survival [7, 8]. This is particularly true of contraceptive services, whose functioning requires sufficient staff training, counselling skills and supplies, and client trust that service quality is good and supplies will continue. In many camp settings, fertility rates and gender-based violence increase, and maternal and neonatal mortality can be high [7, 9]. For example, a World Health Organisation (WHO) study estimated 25–50% of maternal mortality among refugees as due to unsafe abortion, indicating considerable unmet need for contraception . Implementing agencies now recognise the need to provide contraceptive services. However, despite moves to improve provision, barriers to access and acceptability remain [11–14].
From 1989 to 2004, conflicts in Liberia and Sierra Leone displaced over 500,000 people into the Forest Region of neighbouring Guinea . While many Liberians returned home following elections in 1997, civil war in Sierra Leone lasted until 2002. Two major refugee influxes in 1991 and 1997–98 challenged the already weakened Guinean health services, still recovering from disastrous economic and political conditions under Sekou Touré. Following the 1986 Bamako Initiative, Guinea's new government initiated major health sector reforms, encouraging non-governmental agencies to support health service development. Guinea's Ministry of Health responded to refugee health needs through the "Programme d'assistance aux réfugiés Libériens et Sierra Léonais" (PARLS), which soon became an integral part of the health system. Refugees received free treatment from Guinean health services, reimbursed by UNHCR on a fee-for-service basis. However, refugees sometimes perceived government reproductive and sexual health services as deficient. For example, Liberian and Sierra Leonean women had access to family planning (FP) in their home countries, but in Guinean health centres such services were only introduced in 1992.
RHG model summary
Management: 1 coordinator, 1 deputy coordinator, 1 youth coordinator.
Support: 4 supervisors, 1 data officer, 1 finance officer, 1 part-time expatriate advisor (GTZ).
Frontline: 36 nurse/midwives, 75 RHG facilitators, 14 youth/drama groups.
Safe motherhood, FP, syndromic STI management, HIV prevention.
RHG management team was coached by GTZ in NGO internal governance issues, human resource management, project management, monitoring and evaluation, health information systems, survey design, implementation and evaluation.
Contraceptives: oral, injectible, IUD, condoms, and spermicide supplied through health facilities.
STI drugs: antibiotics for refugees from UNHCR, supplied through health facilities.
Other: transport (2 pickups, 2 motorbikes), office and audio/visual equipment from GTZ.
Approximately USD 164,000 annually (1999).
GTZ (core funding, organisational development, technical assistance), ARC (training, funding some facilitators), UNHCR (refugee services coordination, reimbursement of Guinean health services for refugees), Guinean MoH (health facilities).
Health service based: Female refugee nurses and midwives, seconded to 28 Guinean health facilities used by refugees, provided services to refugees and Guineans.
Community based: RHG facilitators provided information, contraceptives (condoms, spermicide) and referral. Theatre groups and youth clubs provided information and entertainment.
RH professionals and motivated community volunteers enabled to plan, provide and evaluate sexual and reproductive health services for their fellow refugees.
Improved RH service provision in Forest Region, increased contraceptive usage and STI prevention and treatment, and became an important actor in the health sector (RHG represented 'best practice' and 'worthy of study' – WHO consultant ).
RHG health education and services appeared to reach women effectively. However, workers were concerned about their effectiveness in reaching men and adolescents, which has been found to be problematic elsewhere [12, 17–27]. In 1999, a cross-sectional survey was conducted in the refugee population to gather population-level data on reproductive health knowledge, attitudes and practices (KAP) for use in strengthening RHG's implementation. The survey collected data on demographics, family planning, sexually transmitted infections (STIs), HIV, antenatal and obstetric care. Study objectives included the assessment of gender or age differences in reproductive health knowledge, attitudes, and practices, which might warrant different approaches for these target groups. This paper addresses gender and age differences in family planning, while STIs are addressed in the companion paper .
The study this paper is drawn from was a cross-sectional, questionnaire-based interview survey on sexual and reproductive health knowledge, attitudes, and practices. The target population was reproductive-age male and female refugees (15 to 49) from an estimated population of 250,000 living in 48 camps across the Forest Region of Guinea, covered by RHG activities for four years. Two planned follow-up surveys were abandoned due to political changes and camp closures.
Sampling was multi-stage. First, 45 clusters of households were randomly selected from the 48 camps, with probability of selection proportional to camp size. Second, a stratified sample of ten men and ten women per cluster (i.e. one eligible man or woman from each of twenty households) was randomly selected from household lists. Sample size was calculated to detect a difference of 10% versus 20% between strata of equal size with 80% power and 95% confidence interval, accounting for clustering. Participation was voluntary, with no payments other than reimbursement of travel costs made. The study received ethical clearance from the Ministry of Public Health in Guinea and the London School of Hygiene & Tropical Medicine in the UK.
The questionnaire was designed from instruments used in similar settings and piloted in a camp not included in the study. Several sections covered socio-demographic information, family planning, sexual health, and antenatal care (only for female interviewees). The questionnaire was intended for use in English, and if respondents were not sufficiently fluent, the interviewer translated directly into local language. Questions were read verbatim to ensure reliability, and only rephrased if a respondent did not understand. Interviewers were recruited from the refugee community, and were always the same sex as respondents. A four-day training course and instruction manual were given to all interviewers, covering aspects such as privacy, prompting and translations. Data collection and entry were conducted over four weeks in 1999. Three contact attempts were made before classification as absent and replacement with another household or individual. Data collection and entry were completed within the study period. Data was double-entered in Epi-Info™ 6, with range and consistency checks to reduce transposition error.
Analysis was conducted using Stata® 10.0. Family planning outcomes were explored for associations with gender and age, using chi-squared tests and Mantel Haenszel odds ratios as appropriate. Potential confounders were determined based on independent association with exposure and outcome variables (i.e. significant at p < 0.05). Confounders that changed odds ratios by at least 10% were incorporated into logistic regression models, which accounted for clustering using robust standard errors. Effect modifiers were reported individually if they changed the effect of exposure on outcome significantly between strata, as determined by Wald test.
Demographic characteristics stratified by gender
Country of origin
Arrival in camp
1996 or later
No formal education
Some formal education
Age at first penetrative sex
15 years or less
16 years or older
Risk of unplanned pregnancy*
Ever married respondents
n = 275 (100)
n = 375 (100)
Respondent or husband has other wife/wives
Residence of partner
Living together in camp
Age at marriage+
10 or under
n = 444 (100)
Parous female respondents
n = 360 (100)
Living children (women)
1–3 children living in household
4–8 children living in household
Family planning knowledge, attitudes and reported practices, by gender
n = 445 (100)
n = 444 (100)
Can explain FP
No. of FP methods known (excluding traditional methods)
Methods identified w/o probing (multiple answers possible)
Other (i.e. traditional methods)
Methods identified with probing (multiple answers possible)
Respondents who explained FP
n = 294 (100)
n = 389 (100)
Key FP information source
Friends and family
X 2 p-value
n = 445 (100)
n = 444 (100)
Attitude to couples using FP
Attitude to RHG facilitators providing FP info
Attitude to FP teaching (to boys)
Before age 15
Around age 15
Later than age 15
Attitude to FP teaching (to girls)
Before age 15
Around age 15
Later than age 15
Respondents currently with partner
n = 251 (100)
n = 320 (100)
Partner's attitude to couples using FP
Don't know partner's attitude
X 2 p-value
n = 445 (100)
n = 444 (100)
Reported use of contraception
Use by respondent/partner (multiple answers possible)
Ever used condoms
Ever used pills
Ever used injections
Ever used spermicides
Ever used IUDs
Contraceptives currently used (multiple answers possible)
Respondents currently with partner
n = 251 (100)
n = 320 (100)
Discussion of FP with partner
1–2 times in last 12 months
More than twice in last 12 months
n= 107 (100)
n= 116 (100)
Where current users access FP
Any other locations
Why FP source was chosen (multiple answers)
Convenience-closer to home
Convenience-use other services
Quality-only available there
Convenience-closer to work/market
n = 338 (100)
n = 328 (100)
Main reason for non-use of modern contraception
Opposed to use
Lack of knowledge
Expected future contraceptive use
Within next 12 months
Current non-users, opposed to FP use
n = 82 (100)
n = 27 (100)
Religion opposed (all)
Female respondents were almost five times more likely to know about family planning concepts and methods than were male respondents (OR 4.8, robust 95% confidence interval 2.9–7.9, adjusted for age, ever married and education). Among those with formal education women had three times higher odds of knowing what family planning was (OR 3.0, robust 95% confidence interval 1.4–6.3, adjusted for age and ever married). Among those with no formal schooling, this difference rose to over six times greater odds (OR 6.4, 3.6–11.1, adjusted for age and ever married). Although the association was only weakly significant (Wald test p-value = 0.07), this suggests that formal education increased the likelihood that men would know about family planning concepts, reducing the knowledge gap between the genders.
RHG facilitators were cited as the main family planning information source for respondents who knew about family planning (67%), though men and women appeared to access health information differently (p < 0.01). While 91% of women and 86% of men got their health information from RHG staff or health facilities, men were more likely than women to get information from friends, radio, and RHG dramas (15% versus 8%).
More than 70% of men and about 90% of women approved of couples using family planning and of RHG facilitators providing information (Table 3b). However, over 40% of respondents reported never having discussed family planning with their partners. Forty-three percent of respondents considered that girls should receive family planning information before age 15, while only 16% felt this to be appropriate for boys. Women responded significantly more positively to attitude questions than did men (p < 0.001), but almost a quarter of women reported not knowing their partner's attitude to family planning. Among respondents who knew what family planning was, women were more than eight times more likely than men were to approve of couples using contraception (OR 8.7, 3.8–20.0, adjusted for education and partner approval of family planning).
More than half of respondents reported never having used modern contraception, and only a quarter identified themselves as current users (Table 3c). Condoms, oral contraceptives, and injections were the most popular. Over 75% of users obtained contraceptives from health facilities. The three main reasons users chose a particular contraceptive source were related to service quality (i.e. privacy, staff competence, staff friendliness). Both women (80%) and men (63%) reported main reasons for not using contraceptives as 'fertility related' (e.g. abstaining, pregnant, lactating, unable or trying to conceive). Opposition to contraceptive use was reported by 24% of men versus 8% of women (p < 0.001). Of those opposed to using contraception, 55% of men and 26% of women, predominantly Muslims, reported this as due to religion (p = 0.02). Among current non-users, odds of expected future contraceptive use were approximately twice as high for women as men (OR 2.19, 1.4–3.5, adjusted for age, education, and ever married).
Over 90% of respondents knew where to access contraceptives, with women slightly more knowledgeable about were to get the pill. Women and men identified at least one correct source for an average of 3.6 and 2.5 contraceptive methods respectively (i.e. condom, pill, injection, IUD, spermicide).
Knowledge of family planning as a concept and approval of couples using family planning did not differ significantly between respondents who were younger or older than 20 years, though knowledge was slightly better among older respondents (OR 1.7, 0.8–3.7, adjusted for parity and ever having married) . Contraceptive use was more frequent in the older age group (OR = 1.5, 1.3–1.8, adjusted for parity and presence of partner in camp).
Those who reported RHG facilitators as their primary information source had non-significantly higher odds of approving of couples using family planning (OR = 1.8, 0.7–4.2, adjusted for parity) and to be current users of contraception (OR = 1.3, 0.7–2.6, adjusted for parity, education, and partner approval of FP). These respondents also had significantly higher odds of discussing family planning with their partners (OR = 2.2, 1.2–3.8, adjusted for parity and education).
Comprehensive studies of reproductive health issues among refugees are still relatively rare. This study enabled insight into the influence of gender on family planning knowledge, attitudes and practices in a camp setting. It supports previous findings that men's education helps to increase family planning awareness and attitudes in the way women's life experience (or parity) appears to do [30–32]. Additional research is necessary on effective ways of targeting men, and improving their reproductive health knowledge, attitudes, and practices in refugee settings.
Findings indicate that RHG clients knew more about family planning, and were more likely to approve of and use contraceptives. The consistency of positive associations between RHG activities and knowledge, attitude and practices for family planning and sexually transmitted disease indicators  suggests that RHG's model (i.e. involving refugee women as active members in a refugee self-help organisation that trained and supported them to provide education and contraceptives to their community) was effective and could possibly be replicated in similar conflict-affected settings [1, 11, 14].
Cross-sectional studies, while enabling exploration of multiple outcomes and exposures, are limited by potential reverse causality as explanatory and outcome variables are measured at the same point in time (e.g. better family planning knowledge may result from attending RHG activities, or RHG attendance might result from better knowledge). Possible reporting and observer bias was minimised through surveyor training and questionnaire piloting. Residual confounding is possible, due to lack of data on certain variables (e.g. socio-economic status, desired family size, gender-based violence), which could influence family planning choices. Chance was reduced using robust standard errors.
Gender and age differences
Education appears a major determinant of men's family planning knowledge, but not of women's knowledge or attitudes. Women were younger and less well educated, yet knew more about family planning and contraceptives. Women are often seen as primarily responsible for family planning, and targeted by reproductive health programming . Possibly, the skills men develop through education enable them to seek knowledge and develop informed opinions on topics to which they might not be exposed otherwise. Additional education may change men's attitude towards gender relations. They may want women as partners who are "more than mothers" . Thus, women's greater ability to contribute to household income could be a reason why men expressed support of family planning and girls' education. Men prioritised non-healthcare information sources, such as radio and dramas, supporting suggestions that men tend to access family planning information in non-health settings [24–26]. It appeared that women respondents learned about family planning through life experience, as knowledge was not significantly influenced by education or exposure to RHG activities (using "time in camp" as proxy). Parity could be a catalyst, as parous women appeared significantly more knowledgeable about family planning than nulliparous women did (p < 0.001). Parity also meant exposure to RHG information during antenatal services.
High reported approval of family planning (80% of respondents) did not correspond with current usage (25%). Main reasons reported for non-use were fertility related (71%). However, usage was much higher than typical for West Africa. UN estimated use of current modern contraceptives for 16 West African countries was 7.9%, with Sierra Leone and Guinea at 3.9% and 4.1% respectively, while RHG's contraceptive coverage was 17% [14, 27]. It is difficult to assess whether use was higher in this population because of greater need or better access, but this relatively high coverage supports the value of RHG's work. Nonetheless, our findings suggest that there was still considerable unmet need for contraception and risk of unplanned pregnancy (69%). Interestingly, only 3.5% of non-users reported the barrier of 'partner opposition' noted in the literature [19, 21, 33]. It is worth noting that respondents rated quality issues higher than cost or distance when choosing contraceptive services.
Findings indicate that adolescents knew somewhat less about family planning, and sexually active young people were somewhat less likely to use contraception, than adults . However, while results suggest additional attention should be given to adolescent reproductive health, fewer age than gender related disparities were found.
Analysis indicates disparities in family planning knowledge and approval between men and women refugees. Given that refugee men know significantly less about family planning and accessed information through peer networks and mass media as well as healthcare providers, communication strategies on family planning in refugee settings could have greater reach with gender-specific messages and communication channels [17, 18, 26]. The international community should support operational research, involving knowledgeable members of the refugee community, on the best methods of supporting men's utilisation of reproductive health and family planning services within their communities [20, 22, 23].
We wish to acknowledge the cooperation and kindness of interviewees, without whom this research would not have been possible. Thanks to local staff and workers, particularly data manager and field supervisors. We wish to acknowledge local authorities, GTZ Guinea and UNHCR for their support, and GTZ for providing funding. Special thanks to John Cleland (LSHTM) for reviewing an earlier version of this paper and to Simon Cousens (LSHTM) for assistance with regression analysis.
- McGinn T, Purdin S: Editorial: Reproductive health and conflict: looking back and moving ahead. Disasters. 2004, 28: 235-238. 10.1111/j.0361-3666.2004.00255.x.View ArticlePubMedGoogle Scholar
- McGinn T: Reproductive health of war-affected populations: what do we know?. International Family Planning Perspectives. 2000, 26: 174-180. 10.2307/2648255.View ArticleGoogle Scholar
- Burns K, Male S, Pierotti D: The Reproductive Health of Refugees. International Family Planning Perspectives. 2000, 26: 161-10.2307/2648252.View ArticleGoogle Scholar
- Schreck L: Turning point: A special report on the refugee reproductive health field. International Family Planning Perspectives. 2000, 26: 162-166. 10.2307/2648253.View ArticleGoogle Scholar
- Alcala M: Action for the 21st Century: Reproductive Health and Rights for All. ICPD. 1994Google Scholar
- UNHCR: 2006 Global Trends: Refugees, Asylum-seekers, Returnees, Internally Displaced and Stateless Persons. 2006, Geneva: Division of Operational Services, Field Information and Coordination Support SectionGoogle Scholar
- Ogata S: Refugee women: the forgotten half. Our Planet. 1995, 7: 19-22.PubMedGoogle Scholar
- Kollie S, von Roenne F, Blankhart D: Readers' Forum: Humanitarian assistance should include aspects of sexuality. Bulletin of the WHO. 1999, 77: 1020.Google Scholar
- Bartlett LA, Jamieson DJ, Kahn T, Sultana M, Wilson HG, Duerr A: Maternal mortality among Afghan refugees in Pakistan, 1999–2000. Lancet. 2002, 359: 643-649. 10.1016/S0140-6736(02)07808-X.View ArticlePubMedGoogle Scholar
- Cohen S: The reproductive health needs of refugees: emerging consensus attracts predictable controversy. Guttmacher Rep Public Policy. 1998, 1: 10-12.PubMedGoogle Scholar
- IAWG: Inter-agency global evaluation of reproductive health services for refugees and internally displaced persons. 2004, Geneva: UNHCRGoogle Scholar
- Degni F, Koivusilta L, Ojanlatva A: Attitudes towards and perceptions about contraceptive use among married refugee women of Somali descent living in Finland. Eur J Contracept Reprod Health Care. 2006, 11: 190-196. 10.1080/13625180600557605.View ArticlePubMedGoogle Scholar
- Whelan A, Blogg J: 'Halfway people': Refugee views of reproductive health services. Global Public Health. 2007, 2: 373-394. 10.1080/17441690701267048.View ArticlePubMedGoogle Scholar
- von Roenne A, Von Roenne F, Kollie S, Swaray Y, Sondorp E, Borchert M: Reproductive Health Services for Refugees by Refugees: An example from Guinea. Disasters.
- Van Damme W, De Brouwere V, Boelaert M, Van Lerberghe W: Effects of a refugee-assistance programme on host population in Guinea as measured by obstetric interventions. Lancet. 1998, 351: 1609-1613. 10.1016/S0140-6736(97)10348-8.View ArticlePubMedGoogle Scholar
- Msuya D: Report on Assessment of Reproductive Health Services for Adolescent Refugees in Guinea's Forest Region. WHO. 1999Google Scholar
- Collumbien M, Hawkes S: Missing messages: does the reproductive health approach respond to men's sexual health needs?. Culture, Health & Sexuality. 2000, 2: 135-150. 10.1080/136910500300769.View ArticleGoogle Scholar
- Chikamata D: Male needs and responsibilities in family planning and reproductive health. Plan Parent Chall. 1996, 2: 8-10.PubMedGoogle Scholar
- Donati S, Hamam R, Medda E: Family planning KAP survey in Gaza. Soc Sci Med. 2000, 50: 841-849. 10.1016/S0277-9536(99)00339-1.View ArticlePubMedGoogle Scholar
- Hossain MB, Phillips JF, Mozumder AB: The effect of husbands' fertility preferences on couples' reproductive behaviour in rural bangladesh. J Biosoc Sci. 2007, 39: 745-757. 10.1017/S0021932006001696.View ArticlePubMedGoogle Scholar
- Kaggwa EB, Diop N, Storey JD: The role of individual and community normative factors: a multilevel analysis of contraceptive use among women in union in Mali. Int Fam Plan Perspect. 2008, 34: 79-88. 10.1363/3407908.View ArticlePubMedGoogle Scholar
- Mullany BC, Becker S, Hindin MJ: The impact of including husbands in antenatal health education services on maternal health practices in urban Nepal: results from a randomized controlled trial. Health Educ Res. 2007, 22: 166-176. 10.1093/her/cyl060.View ArticlePubMedGoogle Scholar
- Mumtaz Z, Salway SM: Gender, pregnancy and the uptake of antenatal care services in Pakistan. Sociol Health Illn. 2007, 29: 1-26.View ArticlePubMedGoogle Scholar
- Odu OO, Ijadunola KT, Komolafe JO, Adebimpe WT: Men's knowledge of and attitude with respect to family planning in a suburban Nigerian community. Niger J Med. 2006, 15: 260-265.PubMedGoogle Scholar
- Sadeghipour Roudsari HR, Sherafat-Kazemzadeh R, Rezaeie M, Derakhshan M: Reproductive health knowledge, attitudes and practices of Iranian and Afghan men in Tehran Province. East Mediterr Health J. 2006, 12: 862-872.PubMedGoogle Scholar
- Sternberg P, Hubley J: Evaluating men's involvement as a strategy in sexual and reproductive health promotion. Health Promotion International. 2004, 19: 389-396. 10.1093/heapro/dah312.View ArticlePubMedGoogle Scholar
- UN Population Division: World Contraceptive Use 2003. 2004, United Nations Department of Economic and Social AffairsGoogle Scholar
- Chen M, von Roenne A, Souare Y, von Roenne F, Ekirapa A, Howard N, Borchert M: Reproductive health services for refugees by refugees in Guinea II: sexually transmitted infections. Conflict & Health in press.
- UNICEF: Innocenti Digest No 7. Early Marriage: Child Spouses. Edited by: Hawke A. 2001, Geneva: Innocenti Research CentreGoogle Scholar
- Chen J, Smith KB, Morrow S, Glasier A, Cheng L: The acceptability of combined oral hormonal contraceptives in Shanghai, People's Republic of China. Contraception. 2003, 67: 281-285. 10.1016/S0010-7824(02)00487-0.View ArticlePubMedGoogle Scholar
- Radecki SE, Beckman LJ: Contraceptive risk-taking in a medically-underserved, low-income population. Women Health. 1994, 21: 1-15.View ArticlePubMedGoogle Scholar
- Wall EM: Valued outcomes in the selection of a contraceptive method. West J Med. 1984, 141: 335-338.PubMed CentralPubMedGoogle Scholar
- van Damme W, De Boelaert M, De Brouwere V, van Lerberghe W: Effects of refugee-assistance programmes on host population in Guinea as measured by obstetric interventions. Lancet. 1998, 351: 1609-1603. 10.1016/S0140-6736(97)10348-8.View ArticlePubMedGoogle Scholar
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