Nigerian Study Sets First SF-36 Quality-of-Life Benchmarks for Adults in Ile-Ife

Researchers have published the first age- and sex-specific normative reference values for health-related quality of life among Nigerian adults measured with the SF-36 Health Questionnaire, drawing on a community-based sample of 2,087 apparently healthy people aged 18 to 74 years in Ile-Ife, Osun State. The cross-sectional study, conducted by a team led by Chidozie Mbada and colleagues and published in the Bulletin of Faculty of Physical Therapy, was designed to fill a gap that has long constrained the interpretation of quality-of-life scores in sub-Saharan Africa: the absence of population-specific reference data against which individual or group results can be judged.

The rationale for the work rests on a methodological point that is easy to overlook. An SF-36 score has limited meaning in isolation, and the International Quality of Life Assessment Project has recommended that countries or population groups establish their own normative data using the instrument. Population-based reference values already exist for developed countries such as the United States and the United Kingdom, but comparable data remain scarce in Nigeria and much of sub-Saharan Africa. In their absence, clinicians and researchers often borrow reference data from other populations, which may not reflect differences in culture, socioeconomic conditions, health status, or healthcare systems. Because quality-of-life scores are sensitive to cultural context, the authors argue that transplanting a normative database from one population to another is problematic.

The SF-36 itself is a 36-item generic instrument first developed in the late 1980s in the United States from the 245-item RAND MOS Questionnaire for the Medical Outcomes Study. When scored, its items are summarised into eight domains: physical functioning, role physical, bodily pain, general health, vitality, social functioning, role emotional, and mental health. The first four domains combine into a physical component summary, and the remaining four into a mental component summary. Scores range from 0 to 100, with higher values indicating better function or health. The instrument is among the most extensively validated generic quality-of-life measures and is the most frequently used, which makes it a natural choice for building comparative reference data.

Participants were recruited using a multistage random sampling technique from two settings: Obafemi Awolowo University, where students were drawn from four randomly selected halls of residence and staff from ten randomly selected academic and administrative departments, and the surrounding community of Ile-Ife, where five of the eleven political wards in Ife Central Local Government Area were randomly selected and every odd-numbered household approached. Eligible participants were apparently healthy Nigerian adults aged 18 or older who reported no physician-diagnosed chronic conditions, acute illness, cognitive impairment, or current treatment affecting quality of life, could communicate in English, and gave informed consent. The target of more than 2,000 participants was guided by European Social Survey recommendations that population-based surveys aiming at stable normative estimates enrol at least 1,500 people. The final sample comprised 1,157 men, or 55.4 percent, and 930 women, or 44.6 percent, with a mean age of 33.2 years and a standard deviation of 15.1 years.

The sample was predominantly Yoruba, at 85.6 percent, Christian, at 68.1 percent, single, at 58.0 percent, and tertiary-educated, at 79.5 percent. Across all ages, the highest mean score among the eight scales was observed on general health, at 82.5, and the lowest on vitality, at 73.9. Men recorded higher mean scores than women across scales and domains, and younger adults consistently reported better quality of life than older ones. The highest physical component summary score, 83.7, and the highest mental component summary score, 77.7, were observed among participants aged 18 to 24 years, while those aged 65 and older recorded the lowest values, at 51.1 for the physical summary and 57.5 for the mental summary. The study also published percentile distributions, so that an individual’s score can be located within the distribution for their age and sex group, with the 50th percentile representing the median and the 95th percentile a score exceeded by roughly five percent of the reference group.

To examine sociodemographic correlates, the researchers used Spearman’s rank correlation, an unadjusted exploratory analysis, with statistical significance set at p below 0.05. Age, sex, and marital status each showed significant inverse but weak correlations with the SF-36 scales and domains. Education showed a significant inverse but weak correlation with all scales and domains. Religion was weakly correlated with general health, vitality, mental health, and the mental component summary, while ethnicity correlated significantly but weakly with physical functioning only. Crucially, although these associations reached statistical significance, the correlation coefficients were generally weak, with absolute values below 0.30, meaning the sociodemographic characteristics explained only a small proportion of the variability in quality-of-life scores.

The sex and age patterns carry practical weight for anyone interpreting SF-36 results in this population. The authors emphasise that the variability in subscale and domain scores by sex and age underlines the need to use age- and gender-specific normative data rather than a single pooled reference. Men reported better quality of life than women, particularly in physical health, with a physical component mean of 80.88 for men against 76.32 for women, and a physical functioning mean of 81.31 for men against 76.75 for women. Mean scores declined with increasing age regardless of sex, and the poorest self-reported health was recorded in the 65-and-over group. The authors suggest that the male advantage may relate to the socioeconomic structure of Nigerian society, while the age decline may reflect reduced participation in physical activity and age-related musculoskeletal changes, though these are interpretive suggestions rather than demonstrated mechanisms in this cross-sectional data.

Comparisons with international normative data highlight why local reference values matter. Compared with published norms from the USA, UK, Canada, and Hong Kong, the Nigerian sample showed higher mean scores for general health, vitality, and bodily pain, but lower mean scores for physical functioning, role physical, and social functioning. The authors caution that such differences should be interpreted carefully, since they may reflect variations in cultural perceptions of health, family support systems, socioeconomic conditions, religious practices, and healthcare access, as well as differences in study populations and sampling methods. They also note that population-based SF-36 normative data from sub-Saharan Africa are so limited that even regional comparisons are difficult; a Ghanaian study in urban Accra, for example, focused on psychometric evaluation of the instrument rather than establishing normative reference values.

The study’s limitations are set out explicitly and shape how the norms should be used. Data were collected from a single geographical region, which may limit broader applicability, and some demographic subgroups may have been insufficiently represented. The cross-sectional design precludes causal inference and cannot capture temporal change. Responses were self-reported, introducing possible recall and response bias, and only literate adults able to complete a self-administered English questionnaire were included, potentially limiting applicability to populations with lower literacy. The number of people approached and those who declined was not recorded, so no response rate could be calculated and non-response and selection bias cannot be excluded. Finally, because the correlates were examined with unadjusted bivariate analyses, independent associations cannot be inferred; the observed correlations may be influenced by interrelationships among the sociodemographic variables themselves.

Within those boundaries, the authors position the new tables as a practical benchmarking resource. The normative values may help clinicians and researchers interpret SF-36 scores among Nigerian adults, support the evaluation of treatment outcomes and population health interventions, and provide reference data for epidemiological studies, healthcare planning, and public health policy. The team describes the work as, to their knowledge, one of the largest community-based efforts to establish age- and sex-specific SF-36 normative values and the first among Nigerian adults. They are clear that the estimates are validated for the sampled population rather than the nation as a whole, and they call for future studies using nationally representative samples and longitudinal designs to validate and extend the reference values into comprehensive norms for Nigeria.

Subject of Research: Normative SF-36 health-related quality of life reference values and sociodemographic correlates among adults in Ile-Ife, Nigeria

Article Title: Normative values and sociodemographic correlates of health-related quality of life among Nigerians using the SF-36 Health Questionnaire

Article References: Mbada, C., Frank, I., Adegbemigun, O., Ademoyegun, A. B., Gebrye, T., & Fatoye, F. (2026). Normative values and sociodemographic correlates of health-related quality of life among Nigerians using the SF-36 Health Questionnaire. Bulletin of Faculty of Physical Therapy, 31(1), Article 42. https://doi.org/10.1186/s43161-026-00383-6

Image Credits: AI Generated

DOI: 10.1186/s43161-026-00383-6

Keywords: health-related quality of life, SF-36 questionnaire, normative values, Nigeria, cross-sectional study, sociodemographic correlates, Ile-Ife, physical component summary, mental component summary, population health, survey research, sub-Saharan Africa