Collection of salivary cortisol has become increasingly popular in large population-based

Collection of salivary cortisol has become increasingly popular in large population-based studies. associated with cortisol estimates as well as FK-506 whether FK-506 associations of cortisol with both compliance and socio-demographic characteristics were robust to adjustments for one another. We further assessed the day-to-day reliability for cortisol features and the extent to which reliabilities vary according to socio-demographic factors and sampling protocol compliance. Overall we found higher compliance among persons with higher levels of income and education. Lower compliance was significantly associated with a less pronounced cortisol awakening response (CAR) but was not associated with any other cortisol features and adjustment for compliance did not affect associations of socio-demographic characteristics with cortisol. Reliability was higher for area under the curve (AUC) and wake up values than for other features but generally did not vary according to socio-demographic characteristics with few exceptions. Our findings regarding intra-class correlation coefficients (ICCs) support prior research indicating that multiple day collection is preferable to single day collection particularly for CAR and slopes more so than wakeup and AUC. There were few differences in reliability by socio-demographic characteristics. Thus it is unlikely that group-specific sampling protocols are warranted. is the estimated between-individual variance for a given feature for the kth group of the PIK3R5 demographic factor and is the between-day variance for the feature. This quantity reflects the similarity or correlation of the features within individuals and ranges from 0 (no similarity in the feature values across days) to 1 1 (values are the same for all those days) (Park and Lake 2005 Note that when estimating the ICCs the single model approach that we employed is equivalent to fitting multiple models separately for each category of the socio-demographic factors. However the single model approach provides the benefit of allowing us to compute the = 0.07). Table 2 Percent of FK-506 individuals within each category of selected socio-demographic characteristics by categories of compliance score. Table 3 presents the crude and adjusted associations FK-506 of compliance with each of the five cortisol features investigated. The coefficients reflect log relative differences in cortisol features according to levels of compliance (top) since cortisol levels were log transformed prior to constructing the features. Standardized coefficients (bottom) allow direct comparisons of the association with compliance across different features. People in the lowest tertile of compliance scores had CARs that were 9% lower (?0.09 in log-scale; 95% C.I.: ?0.18 ?0.01) than those in the highest tertile of compliance scores on average prior to adjustment for covariates. This association is usually attenuated by 15% after adjustment for socio-demographic covariates (0.08 log-scale units lower in the low versus high compliance group (95% C.I.: ?0.16 0 The 0.09 difference is equivalent to 0.15 of a standard deviation of the (log) CAR distribution. Compliance was not significantly related to wake up early decline (30 minutes to 2 hours post-awakening) late decline (2 to 16 hours post-awakening) or total cortisol output (AUC). The magnitude of the associations between compliance and these four additional features was less than 0.09 standard deviations of the distributions of the features. Table 3 Mean differences in selected cortisol features associated with categories of compliance score (high compliance as the reference) before and after adjustment for socio-demographic characteristics. Estimates are shown for cortisol values log-transformed … Table 4 shows associations of socio-demographic characteristics with each cortisol feature before and after adjustment for compliance scores with significant associations in bold face. Among those significant associations adjustments for compliance never resulted in more than 10% change in FK-506 the coefficients. Among the remaining nonsignificant associations eleven of them changed by more than 10% after adjustment for compliance. There were no changes in direction of associations or in the levels of significance of =0.08). The ICC for early decline differed significantly according to compliance scores and age. People who were more compliant with the sampling protocol and.