Regression analysis for secondary response variable in a case-cohort study

Analysis of secondary failure time responses in studies with response-dependent sampling schemes

Response-dependent sampling is routinely used as an enrichment strategy in the design of family studies investigating the heritable nature of disease. In addition to the response of primary interest, investigators often wish to investigate the association between biomarkers and secondary responses related to possible comorbidities. Statistical analysis regarding genetic biomarkers and their association with the secondary outcome must address the biased sampling scheme involving the primary response. In this article, we develop composite likelihoods and two-stage estimation procedures for such secondary analyses in which the within-family dependence structure for the primary and secondary outcomes is modeled via a Gaussian copula. The dependence among responses within family members is modeled based on kinship coefficients. Auxiliary data from independent individuals are exploited by augmenting the composite likelihoods to increase precision of marginal parameter estimates and enhance the efficiency of estimators of the dependence parameters. Simulation studies are carried out to evaluate the finite sample performance of the proposed method, and an application to a motivating family study in psoriatic arthritis is given for illustration.

Brand-specific rates of pertussis disease among Wisconsin children given 1-4 doses of pertussis Vaccine, 2010-2014

BACKGROUND

Acellular pertussis vaccines were initially licensed based on placebo-controlled efficacy trials, but such trials are no longer ethical. The effectiveness of current pertussis vaccines among properly vaccinated children <5 years is so high that a randomized trial is infeasible. Fluctuations in pertussis incidence and characteristics of the US vaccine marketplace make selection of suitable controls for a case-control study problematic. To satisfy an FDA requirement to evaluate rates of pertussis following licensure of Pentacel® vaccine, we used a case-cohort study design with a novel method for characterizing the cohort population.

METHODS

This prospective, observational study was conducted in Wisconsin from 2010 to 2014 among Wisconsin residents <60 months of age who received ≤four doses of pertussis vaccine (surveillance population). Cases were identified by the Wisconsin Division of Public Health. Characteristics and pertussis vaccinations of the surveillance population were estimated by ongoing random telephonic survey. The primary objective was to determine rates of pertussis disease among those who received only Pentacel vaccine (Group 1) vs those who received a single brand of vaccine other than Pentacel vaccine (Group 2).

RESULTS

1195 pertussis cases were identified. It was estimated that the surveillance population accrued a total of 1,133,403 person-years (Group 1, 39%; Group 2, 41%; Group 3 [those not in Group 1 or Group 2], 20%). Pertussis rates were similar in Group 1 (98.9/100,000) and Group 2 (96.2/100,000); rate ratios were 1.03 (unadjusted; 90% CI, 0.92-1.15) and 0.99 (adjusted; 90% CI, 0.89-1.12). Persons with one or more delayed vaccinations had a 66% higher risk of pertussis (90% CI, 39-96%).

DISCUSSION

Pertussis protection was not found to differ for recipients of the newly licensed vs other available pertussis vaccines. Delayed vaccination substantially increased risk of pertussis. Sample survey methodology was able to characterize the study cohort and enable an otherwise-infeasible study. Clinical Trial Registry number: ClinicalTrials.gov, NCT01129362.