A Feasibility, Reliability & Confirmatory Factor Analysis of the Health-Related Quality of Life Measure SF-36 in low-income, urban African-American women at HIV risk

Daniel Fuhrmann, PhD, University of Wisconsin-Milwaukee

Wisconsin Illinois SAS Users ConferenceJune 24, 2015

The “Stories To Tell” Project

Motivation for the “Stories To Tell” Project

“Examine factors corresponding to the four levels of the Bioecological Systems Theory model (Bronfenbrenner, 1995) – individual, interpersonal, community, and socio-cultural factors – and to investigate their relationship with measures of sexual risk behavior, substance use, and trauma/victimization history among African-American women of lower socioeconomic status

STT data on the SF-36 HRQoL measure were used for the present study.

Brief Introduction to HRQoL MeasuresExample: Short-Form 36 Health Survey

What is quality of life?

“Quality of life (QOL) is a broad multidimensional concept that usually includes subjective evaluations of both positive and negative aspects of life. […] Although health is one of the important domains of overall quality of life, there are other domains as well—for instance, jobs, housing, schools, the neighborhood. Aspects of culture, values, and spirituality are also key aspects of overall quality of life that add to the complexity of its measurement.”

Source: The WHOQOL Group. The World Health Organization Quality of Life Assessment (WHOQOL). Development and psychometric properties. Soc Sci Med 1998;46:1569-1585.

What is health-related quality of life?

“The concept of health-related quality of life (HRQOL) and its determinants have evolved since the 1980s to encompass those aspects of overall quality of life that can be clearly shown to affect health—either physical or mental. On the individual level, this includes physical and mental health perceptions and their correlates—including health risks and conditions, functional status, social support, and socioeconomic status.”

Source: http://www.cdc.gov/hrqol/concept.htm

Short-Form Health Survey (SF-36)

• Health-related quality of life (HRQoL) instrument• 36 questions, 8 subscales, 2 component summary scores• Ordinal item scores were conceptualized to be

converted to values ranging from 0 to 100. Higher values represent better health (less disability).• Early studies treated converted scores as continuous items

(Ware et al. 1993)• Later research suggested items should be regarded as

ordered categorical (Keller et al., 1998) and the two component summary scores should be allowed to correlate (Farivar et al., 2007; Buchholz et al., 2008)

Applications of the SF-36 (Selected)

Utilized in thousands of published studies/papers:Evaluate patients’ health status by disease (stroke, kidney

disease, hypertension, etc.) and/or race/ethnicity subpopulation (African-Americans, Latinos, Whites, etc.)

Measure, track, and compare disease burden over timeDetermine cost-effectiveness of health interventions

Only very few studies published on at-risk subpopulation of low-income, African-American women.

SF-36 | Factor Structure:Physical and Mental Health Domains

Physical Health Mental HealthPhysical Functioning Energy/Fatigue

Role Limitations-Physical Social Functioning

Bodily Pain Role Limitations-Emotional

General Health Emotional Well-Being

Empirical Methods

Feasibility and Reliability

Relative Frequencies of Item-Nonresponse

Crohnach’s alpha and ordinal alpha coefficients (based on Pearson and Polychoric correlations)Cronbach’s coefficient alpha is a measure of squared

correlation between observed scores and true scores. Therefore, reliability is measured in terms of the ratio of true score variance to observed score variance.

Confirmatory Factor Analysis (CFA)

Factor analysis is a statistical method used to find a small set of unobserved variables (also called latent variables, or factors) which can account for the covariance among a larger set of observed variables (also called manifest variables).

Confirmatory factor analysis (CFA) is theory- or hypothesis drivenCFA allows researchers to test hypotheses about a particular

factor structureCFA corresponds to the measurement model of SEMMany Goodness-of-fit measures exist. Here, cut-off values for

“good” model fit were: CFI/TLI > 0.95; RMSEA < 0.05; WRMR < 1.0; Chi-Square p-value > 0.05

Results

Demographic Characteristic Full Sample (n=294) Analytic Sample (n=270)Race/Ethnicity

Non-Hispanic Black 272 (92.5%) 259 (95.9%)Non-Hispanic Multiracial 5 (1.7%) 5 (1.9%)Hispanic Black 3 (1.0%) 3 (1.1%)Missing/Refused 14 (5.4%) 3 (1.1%)

Marital StatusUnmarried 234 (79.6%) 216 (80.0%)Unmarried, living with partner 15 (5.1%) 13 (4.8%)Married 12 (4.1%) 12 (4.4%)Divorced 15 (5.1%) 15 (5.6%)Separated 11 (3.7%) 11 (4.1%)Widowed 2 (0.7%) 2 (0.7%)Missing/Refused 5 (1.7%) 1 (0.3%)

Employment StatusFull-time 91 (31.0%) 86 (31.9%)Part-time 56 (19.0%) 54 (20.0%)Unemployed and looking 69 (23.5%) 63 (23.3%)Unemployed and not looking 11 (3.7%) 10 (3.7%)Student or other training 18 (6.1%) 17 (6.3%)Disabled 41 (13.9%) 37 (13.7%)Other 2 (0.7%) 1 (0.4%)Missing/Refused 6 (2.0%) 2 (0.7%)

Number of Children under 18 1.948 (1.510) 1.962 (1.537)Missing/Refused 8 (2.7%) 4 (1.5%)

Years of Education (in years) 12.42 (1.730) 12.45 (1.737)Missing/Refused 5 (1.7%) 1 (0.4%)

Age (in years) 32.0 (6.978) 32.3 (6.963)Missing/Refused 15 (5.1%) 9 (3.3%)

Monthly Income (in dollars) $1,304.22 (2283.01) $1,331.07 (2354.18)

Table 1. Demographics of the Full and Analytic Samples at Baseline Time point (frequencies reported with percentages in parentheses; means reported with standard deviations in parentheses)

Model Χ2(df) Χ2 p CFI TLI RMSEA (90% C.I.) WRMRI. Conceptual SF-36 Model

966.143 (551)

< 0.0001 0.968 0.966 0.053 (0.047,0.058)/ 

1.197

II. Modified SF-36 Model

885.153 (550)

< 0.0001 0.974 0.972 0.048 (0.042,0.053) 1.113

III. Hybrid SF-36 Model

834.237 (552)

< 0.0001 0.963 0.960 0.044 (0.037,0.049) 0.954

Table 2.    Summary of model fit criteria for the conducted confirmatory factor analyses

: Value indicates good model fit

: Value does not indicate good model fit

Item λ r2 Dimensions αpearson αpolychoric α RANDVigorous activities 0.817 0.668 Physical Functioning 0.93 0.97 0.93Moderate activities 0.884 0.782Lift, carry groceries 0.909 0.826Climb several flights 0.899 0.808Climb one flight 0.920 0.847Bend, kneel, stoop 0.882 0.777Walk more than a mile 0.962 0.925Walk several blocks 0.938 0.880Walk one block 0.869 0.755Bathing or dressing 0.815 0.664Cut down time 0.944 0.891 Role Limitations-Physical 0.81 0.92 0.84Accomplished less 0.705 0.497Limited in kind 0.869 0.756Difficulty with work activities 0.944 0.891Cut down time 0.982 0.964 Role Limitations-Emotional 0.80 0.93 0.83Accomplished less 0.911 0.829Not careful 0.803 0.645Full of pep 0.430 0.185 Energy/Fatigue 0.71 0.72 0.86Energy 0.753 0.567Worn out 0.743 0.552Feel tired 0.704 0.496Nervous 0.757 0.573 Emotional Well-Being 0.83 0.86 0.9Down in the dumps 0.861 0.741Calm and peaceful 0.623 0.388Downhearted 0.835 0.698Happy 0.549 0.302Social activities interfered 0.874 0.765 Social Functioning 0.77 0.83 0.85Social activities interfered 0.825 0.680Pain-magnitude 0.790 0.624 Bodily Pain 0.81 0.84 0.78Pain-interference 0.981 0.962General health rating 0.819 0.670 General Health 0.80 0.84 0.78Sick easier 0.683 0.467As healthy 0.708 0.501E t h lth 0 712 0 508

Table 3. Factor loadings and reliability measures for SF‐36 items and dimensions (Model II)

Item Λ r2 DimensionsVigorous activities 0.809 0.655 Physical FunctioningModerate activities 0.887 0.786Lift, carry groceries 0.911 0.829Climb several flights 0.897 0.804Climb one flight 0.922 0.851Bend, kneel, stoop 0.880 0.774Walk more than a mile 0.960 0.921Walk several blocks 0.940 0.883Walk one block 0.872 0.760Bathing or dressing 0.940 0.665Cut down time 0.940 0.884 Role Limitations-PhysicalAccomplished less 0.711 0.506Limited in kind 0.873 0.763Difficulty with work activities 0.944 0.884Cut down time 0.987 0.974 Role Limitations-EmotionalAccomplished less 0.909 0.826Not careful 0.798 0.637Full of pep 0.403 0.162 Energy/FatigueEnergy 0.689 0.474Worn out 0.646 0.417Feel tired 0.630 0.396Nervous 0.711 0.505 Emotional Well-BeingDown in the dumps 0.785 0.616Calm and peaceful 0.600 0.360Downhearted 0.742 0.551Happy 0.583 0.340Social activities interfered 0.824 0.678 Social FunctioningSocial activities interfered 0.768 0.590Pain-magnitude 0.770 0.593 Bodily PainPain-interference 0.912 0.832General health rating 0.621 0.559 General HealthSick easier 0.747 0.386As healthy 0.625 0.390Expect worse health 0.609 0.371

Table 4. Factor loadings for SF‐36 items and dimensions (Model III)

Physical Health Mental HealthPF RP BP GH RE EF EW SF

Current Sample (n=270)M 78.76 68.06 72.35A 63.82 66.05 49.45 68.40B 74.44SD 25.01 37.22 25.49 21.04 39.67 20.38 21.03 25.8625th percentile 65.00 50.00 57.50 35.00 33.33 35.00 52.00 62.5050th percentile 90.00 75.00 77.50 50.00 100.00 50.00 72.00 75.0075th percentile 100.00 100.00 90.00 65.00 100.00 65.00 84.00 100.00Range 5-100 0-100 0-100 5-100 0-100 0-100 4-100 0-100% Ceiling 32.96 46.30 23.70 2.96 50.74 0.74 2.22 34.07% Floor 0.74 15.19 0.74 0.74 18.89 0.37 0.37 1.48

Females age 25-34 (n=275 )M 89.12 86.73 79.61 74.80 82.32 58.04 72.45B 83.07SD 18.72 27.99 20.94 17.24 31.30 20.85 18.62 21.6625th percentile 85.00 100.00 62.00 65.00 66.67 45.00 60.00 75.0050th percentile 95.00 100.00 84.00 77.00 100.00 60.00 76.00 100.0075th percentile 100.00 100.00 100.00 87.00 100.00 75.00 84.00 100.00

Range 0-100 0-100 0-100 10-100 0-100 0-90 8-100 0-100% Ceiling 48.8 77.5 37.9 6.0 70.6 0.0 1.7 51.1% Floor 0.0 4.7 0.2 0.0 7.8 0.4 0.0 0.2

Females age 35-44 (n=264)M 88.06 83.65 74.85A 74.25 80.08 59.43 73.32 83.07SD 17.70 32.21 22.74 19.44 33.88 19.72 16.79 23.2725th percentile 85.00 75.00 62.00 62.00 66.67 45.00 64.00 75.0050th percentile 95.00 100.00 77.00 77.00 100.00 60.00 76.00 93.7575th percentile 100.00 100.00 87.00 87.00 100.00 75.00 84.00 100.00Range 0-100 0-100 5-100 10-100 0-100 5-100 20-100 0-100% Ceiling 38.0 75.2 1.1 10.0 69.3 1.1 2.2 51.3% Floor 0.2 8.4 0.0 0.0 10.4 0.0 0.0 1.2

Table 5. 

Comparison of means, standard deviations, quartiles, ranges, and percent ceiling and floor for subscale scores for the current sample and national estimates forsimilar age and gender populations

Discussion and Conclusion

Discussion

All three CFA models of the SF-36 instrument reached good fit based on RMSEA, CFI and TLI. The conservative Χ2 test of absolute fit rejected all three proposed models. WRMR only fell below 1.0 in Model III, indicating good fit.

Reliability of the SF-36 instrument’s dimensions was confirmed using ordinal alpha coefficients that were appropriately based on polychoric correlations with all values exceeding 0.7.

The HRQOL profile of women in our study indicated lower health in 14 of the 16 pair-wise comparisons of SF-36 subscale scores with national norm scores for females in the 25-44 age cohort

Conclusion Health profile of our study participants is generally lower than

the national norms for females between 25-44 years of age. High variation in SF-36 subscale scores suggests that other,

previously unspecified factors influence the HRQOL of women who are at risk for HIV. We will explore these factors to help guide HIV-related interventions and general health support programs.

Future research will incorporate tests of measurement invariance using data from the 6- and 12-month waves of our study to determine how well the SF-36 model results generalize across time. We will also explore socio-economic factors that might predict variations in observed SF-36 scores.

Acknowledgements

This research was supported by grant number R01-DA023858 from the National Institute on Drug Abuse.

The authors would like to thank Michael Quant and Xiaojing Jia for their assistance with data management.

We also thank Drs. Michael Brondino, Young Cho, and Scott R. Colwell for helpful comments on our modeling strategy.

Co-Authors

Dr. Laura Otto-Salaj, UW-MilwaukeePrincipal Investigator of the “Stories To Tell” study Interim Director, Center for Applied Behavioral Health ResearchAssociate Professor, Department of Social Work

Rachel CusatisDoctoral Student, Department of SociologyResearch Assistant, Center for Applied Behavioral Health

Research

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Appendix

SF-36 | Physical Health Dimension (1/4)

“Physical Functioning” Subscale (PF)Q3 Does your health limit your ability to do vigorous activities?Q4 Does your health limit your ability to do moderately strenuous

activities?Q5 Does your health limit your ability to carry groceries?Q6 Does your health limit your ability to climb several flights of stairs?Q7 Does your health limit your ability to climb one flight of stairs?Q8 Does your health limit your ability to bend or kneel?Q9 Does your health limit your ability to walk more than a mile?

Q10 Does your health limit your ability to walk several blocks?Q11 Does your health limit your ability to walk one block?Q12 Does your health limit your ability to bathe or dress yourself?

SF-36 | Physical Health Dimension (2/4)

“Role Limitations-Physical” Subscale (RF)Q13 Due to your physical health in the past four weeks,

have you cut down the amount of time you spent on work or other activities?

Q14 Due to your physical health in the past four weeks, have you accomplished less than you would like?

Q15 Due to your physical health in the past four weeks, have you been limited in the kind of work or other activities?

Q16 Due to your physical health in the past four weeks, have you had difficulty performing work or other activities?

SF-36 | Physical Health Dimension (3/4)

“Bodily Pain” Subscale (BP)Q21 How much bodily pain have you had during the past

four weeks?Q22 During the past four weeks, how much did pain

interfere with your normal work?

SF-36 | Physical Health Dimension (4/4)

“General Health” Subscale (GH)Q1 In general, how would you say your health is?Q33 I seem to get sick a little easier than other people.Q34 I am as healthy as anybody I know.Q35 I expect my health to get worse.Q36 My health is excellent.

SF-36 | Mental Health Dimension (1/4)

“Energy / Fatigue” Subscale (EF)

Q23 During the past four weeks did you feel full of pep?Q27 During the past four weeks did you have a lot of

energy?Q29 During the past four weeks did you feel worn out?Q31 During the past four weeks did you feel tired?

SF-36 | Mental Health Dimension (2/4)

Social Functioning Sub Scale (SF)Q20 During the past four weeks, to what extent has your

physical or emotional health interfered with your normal social activities?

Q32 During the past four weeks how much of the time has your physical or emotional health interfered with your social activities?

SF-36 | Mental Health Dimension (3/4)

Role Limitations-Emotional Sub Scale (RE)Q17 As a result of emotional problems during the past four

weeks, have you cut down the amount of time you spent on work or other activities?

Q18 As a result of emotional problems during the past four weeks, have you accomplished less than you would like?

Q19 As a result of emotional problems during the past four weeks, did you not do work or other activities as carefully as usual?

SF-36 | Mental Health Dimension (4/4)

Emotional Well-Being Sub Scale (EW)Q24 During the past four weeks have you been a very

nervous person?Q25 During the past four weeks have you felt so down in

the dumps that nothing could cheer you up?Q26 During the past four weeks have you felt calm and

peaceful?Q28 During the past four weeks have you felt

downhearted and blue?Q30 During the past four weeks have you been a happy

person?