Elsevier

Public Health

Volume 142, January 2017, Pages 15-21
Public Health

Original Research
Average vs item response theory scores: an illustration using neighbourhood measures in relation to physical activity in adults with arthritis

https://doi.org/10.1016/j.puhe.2016.08.016Get rights and content

Highlights

  • A majority of individuals with arthritis did not meet physical activity recommendations.

  • Older adults with poorer perceived neighbourhood physical features have decreased physical activity levels.

  • Neighbourhood and physical activity associations were found with item response theory scores, but not average scores.

  • Future work should expand into modern measurement theory using IRT scores.

Abstract

Objectives

Our study had two main objectives: 1) to determine whether perceived neighbourhood physical features are associated with physical activity levels in adults with arthritis; and 2) to determine whether the conclusions are more precise when item response theory (IRT) scores are used instead of average scores for the perceived neighbourhood physical features scales.

Methods

Information on health outcomes, neighbourhood characteristics, and physical activity levels were collected using a telephone survey of 937 participants with self-reported arthritis. Neighbourhood walkability and aesthetic features and physical activity levels were measured by self-report. Adjusted proportional odds models were constructed separately for each neighbourhood physical features scale.

Results

We found that among adults with arthritis, poorer perceived neighbourhood physical features (both walkability and aesthetics) are associated with decreased physical activity level compared to better perceived neighbourhood features. This association was only observed in our adjusted models when IRT scoring was employed with the neighbourhood physical feature scales (walkability scale: odds ratio [OR] 1.20, 95% confidence interval [CI] 1.02, 1.41; aesthetics scale: OR 1.32, 95% CI 1.09, 1.62), not when average scoring was used (walkability scale: OR 1.14, 95% CI 1.00, 1.30; aesthetics scale: OR 1.16, 95% CI 1.00, 1.36).

Conclusion

In adults with arthritis, those reporting poorer walking and aesthetics features were found to have decreased physical activity levels compared to those reporting better features when IRT scores were used, but not when using average scores. This study may inform public health physical environmental interventions implemented to increase physical activity, especially since arthritis prevalence is expected to be close to 20% of the population in 2020. Based on NIH initiatives, future health research will utilize IRT scores. The differences found in this study may be a precursor for research on how past and future treatment effects may vary between these two types of measurement scores.

Introduction

Health outcome models often use average or sum scores from classical test theory. We modelled both classical test theory (or average) scores and modern measurement theory (or item response theory [IRT]) scores. These two measurement frameworks are supposedly comparable yet their comparisons are novel.1

IRT models describe the relationship between item responses and latent constructs in terms of item and person parameters.2 The item parameters, which are very often the primary focus of an IRT analysis, tell us things like 1) what range of the construct do the items measure?; 2) do the items measure the construct well or poorly?; and 3) do any of the items behave in unexpected ways? These are very useful questions when one is developing or evaluating a scale. The other part of the model is the person parameter. In IRT, there is an estimate for each individual (which is oven called an ‘IRT scale score’ or ‘IRT score’ for short), which takes this rich item-level information and applies it to the individual pattern of responses to produce a score that takes into account everything learned during the IRT analysis. As such, an IRT score considers not only how many items were endorsed, but which items were endorsed. Unless the items are very similar in their parameters, this has the effect of creating different scores for each pattern of responses to a set of items. In classical test theory (CTT), a measurement paradigm most often associated with coefficient alpha, scores are created by adding (or averaging) item responses. This is equivalent to unit-weighting each response. It also imposes equal steps between Likert-type responses (i.e. there is one unit between a 2 and 1 and one unit between a 3 and 2) and further constrains all items to have the exact same steps. To the extent that an IRT model with varying parameters fits a data set well (i.e. better than a model that constrains everything to be equal), one could anticipate that the resulting IRT scores should better reflect the construct of interest.

As an illustration, we used average scores and IRT scores to examine the relation of the perceived neighbourhood physical features with individual physical activity levels in a cohort of adults with arthritis. Studies have consistently identified possible perceived neighbourhood physical environmental barriers as risk factors for decreased physical activity levels among older adults.3, 4 A clearer understanding of the neighbourhood-level risk factors correlated with physical activity among individuals with arthritis will help to develop and implement interventions targeting the perceived neighbourhood physical environment.

In summary, the purposes of this study were to 1) determine whether perceived neighbourhood physical features are associated with physical activity levels in adults with arthritis; and 2) determine whether the conclusions are more precise when item response theory (IRT) scores are used or when average scores are used for the perceived neighbourhood physical features scales. We focus on two perceived neighbourhood physical features, a built factor (walkability) and a social capital factor (aesthetics).4 We hypothesize that participants with a poorer perceived neighbourhood environment will have a decreased physical activity level compared to participants with enriched perceived physical neighbourhood features. Additionally, we hypothesize that the use of the IRT scores will impact the conclusions reached by being more precise.

Section snippets

Sample

This is a cross-sectional survey of adults (n = 2420) from the Individual and Community Social Determinants of Arthritis Outcomes Study (SODE) which was initiated in 2006 as a telephone follow-up survey to the North Carolina Family Medicine Research Network, a practice-based network cohort devoted to research on chronic diseases in primary care in North Carolina.5 This network cohort was purposefully sampled to represent both the urban and rural communities and the ethnic diversity of North

Results

Out of the 2420 individuals from the North Carolina Family Medicine Research Network who agreed to be contacted, 1541 completed the survey with a response rate of 65.2%. Of this sample, 937 adults self-identified as having doctor diagnosed arthritis (including osteoarthritis, rheumatoid arthritis, or fibromyalgia) and 910 provided complete data for our models.

For the AE analyses, the one-dimensional CFA model revealed some local dependence. To avoid any potential local dependence in the IRT

Discussion

In the present large cross-sectional study, we evaluated the relation of perceived neighbourhood physical features, specifically walkability and aesthetics, with individual physical activity levels in adults with self-reported doctor diagnosis of arthritis. Results of this study indicate that individuals with poorer perceived neighbourhood physical features have decreased individual physical activity levels compared to participants with better-perceived neighbourhood physical features. These

Acknowledgements

The authors want to acknowledge the participating family practices in the NC-FM-RN, including Black River Health Services, Burgaw; Bladen Medical Associates, Elizabethtown; Blair Family Medicine, Wallace; Cabarrus Family Medicine, Concord; Cabarrus Family Medicine, Harrisburg; Cabarrus Family Medicine, Kannapolis; Cabarrus Family Medicine, Mt Pleasant; Chatham Primary Care, Siler City; Carolinas Medical Center Biddle Point, Charlotte; Carolinas Medical Center North Park, Charlotte; Community

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