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A Simulation Study of Categorizing Continuous Exposure Variables Measured with Error in Autism Research: Small Changes with Large Effects

Author

Listed:
  • Karyn Heavner

    (Department of Environmental and Occupational Health, School of Public Health, Drexel University, Philadelphia, PA 19104, USA)

  • Igor Burstyn

    (Department of Environmental and Occupational Health, School of Public Health, Drexel University, Philadelphia, PA 19104, USA
    Drexel Autism Institute, School of Public Health, Drexel University, Philadelphia, PA 19104, USA
    Department of Epidemiology and Biostatistics, School of Public Health, Drexel University, Philadelphia, PA 19104, USA)

Abstract

Variation in the odds ratio (OR) resulting from selection of cutoffs for categorizing continuous variables is rarely discussed. We present results for the effect of varying cutoffs used to categorize a mismeasured exposure in a simulated population in the context of autism spectrum disorders research. Simulated cohorts were created with three distinct exposure-outcome curves and three measurement error variances for the exposure. ORs were calculated using logistic regression for 61 cutoffs (mean ± 3 standard deviations) used to dichotomize the observed exposure. ORs were calculated for five categories with a wide range for the cutoffs. For each scenario and cutoff, the OR, sensitivity, and specificity were calculated. The three exposure-outcome relationships had distinctly shaped OR (versus cutoff) curves, but increasing measurement error obscured the shape. At extreme cutoffs, there was non-monotonic oscillation in the ORs that cannot be attributed to “small numbers.” Exposure misclassification following categorization of the mismeasured exposure was differential, as predicted by theory. Sensitivity was higher among cases and specificity among controls. Cutoffs chosen for categorizing continuous variables can have profound effects on study results. When measurement error is not too great, the shape of the OR curve may provide insight into the true shape of the exposure-disease relationship.

Suggested Citation

  • Karyn Heavner & Igor Burstyn, 2015. "A Simulation Study of Categorizing Continuous Exposure Variables Measured with Error in Autism Research: Small Changes with Large Effects," IJERPH, MDPI, vol. 12(8), pages 1-37, August.
  • Handle: RePEc:gam:jijerp:v:12:y:2015:i:8:p:10198-10234:d:54681
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    Cited by:

    1. Karyn Heavner & Craig Newschaffer & Irva Hertz-Picciotto & Deborah Bennett & Igor Burstyn, 2015. "Pooling Bio-Specimens in the Presence of Measurement Error and Non-Linearity in Dose-Response: Simulation Study in the Context of a Birth Cohort Investigating Risk Factors for Autism Spectrum Disorder," IJERPH, MDPI, vol. 12(11), pages 1-20, November.

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