Self-reported anthropometric variables differ from corresponding measurements due to random and systematic reporting errors, and to changes over time in the actual characteristics of participants.
With a number of highly visible studies both in the natural sciences and in political science using such data to shed light on the complex mechanisms underlying violent conflict, researchers have recently raised issues of systematic (reporting) biases.
First, the NHANES data are based on self-report and are subject to random and systematic reporting errors.
To help mitigate the likelihood of systematic reporting errors, well-trained interviewers used a standard questionnaire to collect information from study participants.
A regression dilution ratio close to 1 therefore indicates that there is little combined effect of random and systematic reporting errors.
While we believe this measure reduced systematic reporting bias and enhanced the reliability of SODIS-use measurement, it reduced the total observation time available for analysis.
Systematic reporting errors may also contribute to confounding of estimated associations, which we assessed for each variable by plotting mean NSHD values against mean MWS values according to pre-specified categories of each MWS variable.
Indeed, examination of random and systematic reporting errors and their effects on estimates of disease-exposure associations should be routine in all studies that are based on self-reported exposure data.
Systematic reporting focused on the most severe cases of leptospirosis has the potential for providing a data-driven basis for ministry-level policy development, institution of public health control measures, and quantitative assessment of the global severity of leptospirosis.
Pearson correlations were somewhat larger than the intraclass correlations for waist circumference (0.74 versus 0.59), waist-to-hip ratio (0.52 versus 0.41) and waist-to-height ratio (0.75 versus 0.60), consistent with greater systematic reporting errors for these variables.
Future studies need to incorporate health examinations and biomarkers within household surveys in order to improve the validity of self-reported health states and to detect and correct systematic reporting biases.
