Abstract
BackgroundRecorded serum 25(OH)D in survey data varies with observed and unobserved respondent characteristics. The aim of this study was to expose latent population sub-groups and examine variation across groups regarding relationships between serum 25(OH)D and observable characteristics.MethodsThis study explored the role of unobserved heterogeneity on associations between surveyed 25(OH)D and various factors using a sample (n = 2,641) extracted from the Saudi Health Interview Survey (2013). Linear regression and finite mixture models (FMM) were estimated and compared. The number of latent classes in the FMM was chosen based on BIC score.ResultThree latent classes were identified. Class I (39.82%), class II (41.03%), and class III (19.15%) with mean 25(OH)D levels of 22.79, 34.88, and 57.45 ng/ml respectively. Distinct patterns of associations with nutrition, behaviour and socio-demographic variables were recorded across classes that were not revealed in pooled linear regression.ConclusionFMM has the potential to provide additional insights on the relationship between 25(OH)D levels and observable characteristics. It should be more widely considered as a method of investigation in this area.
Highlights
This study explored the role of unobserved heterogeneity on associations between surveyed 25(OH)D and various factors using a sample (n = 2,641) extracted from the Saudi Health Interview Survey (2013)
finite mixture models (FMM) has the potential to provide additional insights on the relationship between 25(OH)D levels and observable characteristics. It should be more widely considered as a method of investigation in this area
Given the high global prevalence of vitamin D deficiency [5] and its impact on health, it is unsurprising that the identification of factors which elevate the risk of deficiency should attract the interest of researchers
Summary
Studies examining the causes and consequences of vitamin D deficiency, have seen the use of multiple thresholds to define deficiency [10] In many instances this is understandable given thresholds may differ for specific outcomes (such as bone health as opposed to muscle weakness for example); or populations (expectant mothers as opposed to otherwise healthy adults, for example). While some US studies [10] use a threshold of 20 ng/ml to define deficiency and others [7] 10 ng/ml as the concentration of serum 25-hydroxyvitamin D [25(OH)D] for otherwise healthy adults, in the UK others have suggested 12 ng/ml [11] In this context in practical terms this leaves the researcher seeking to distinguish between groups in terms of risk exposure or to characterise membership of those groups in the invidious position of assessing the robustness of findings by testing multiple thresholds without a clear rationale for selecting one over the other. The aim of this study was to expose latent population sub-groups and examine variation across groups regarding relationships between serum 25(OH)D and observable characteristics
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