The effect of health insurance on childhood cancer survival in the United States : Insurance and Childhood Cancer Survival

Measurement error in explanatory variables and unmeasured confounders can cause considerable problems in epidemiologic studies. It is well recognized that under certain conditions, nondifferential measurement error in the exposure variable produces bias towards the null. Measurement error in confounders will lead to residual confounding, but this is not a straightforward issue, and it is not clear in which direction the bias will point. Unmeasured confounders further complicate matters. There has been discussion about the amount of bias in exposure effect estimates that can plausibly occur due to residual or unmeasured confounding. In this paper, the authors use simulation studies and logistic regression analyses to investigate the size of the apparent exposure-outcome association that can occur when in truth the exposure has no causal effect on the outcome. The authors consider two cases with a normally distributed exposure and either two or four normally distributed confounders. When the confounders are uncorrelated, bias in the exposure effect estimate increases as the amount of residual and unmeasured confounding increases. Patterns are more complex for correlated confounders. With plausible assumptions, effect sizes of the magnitude frequently reported in observational epidemiologic studies can be generated by residual and/or unmeasured confounding alone. Show more

For a study with an event time as the endpoint, its survival function contains all the information regarding the temporal, stochastic profile of this outcome variable. The survival probability at a specific time point, say t, however, does not transparently capture the temporal profile of this endpoint up to t. An alternative is to use the restricted mean survival time (RMST) at time t to summarize the profile. The RMST is the mean survival time of all subjects in the study population followed up to t, and is simply the area under the survival curve up to t. The advantages of using such a quantification over the survival rate have been discussed in the setting of a fixed-time analysis. In this article, we generalize this approach by considering a curve based on the RMST over time as an alternative summary to the survival function. Inference, for instance, based on simultaneous confidence bands for a single RMST curve and also the difference between two RMST curves are proposed. The latter is informative for evaluating two groups under an equivalence or noninferiority setting, and quantifies the difference of two groups in a time scale. The proposal is illustrated with the data from two clinical trials, one from oncology and the other from cardiology. Show more

Timely access to quality healthcare has become an increasingly important public health concern over the years. Early diagnosis of cancer is a fundamental goal in oncology because it allows an opportunity for timely treatment while disease burden is still in its earliest stages. Consequently, prognosis may improve, and a cure can be attained with minimal side or late effects. This review examined delays present in diagnosis of childhood cancers and factors that influence these delays. An extensive search of the literature published before April 15, 2007 was conducted for studies that evaluated any type of delay along the cancer-care continuum. Twenty-three studies were included. Diagnosis delay varied across studies. Physician delays were generally longer than those consequent to parents' or patients' recognition of underlying disease. Causes of delays can be grouped into 3 categories: patient and/or parent, disease, and healthcare. The main factors related to diagnosis delay were the child's age at diagnosis, parent level of education, type of cancer, presentation of symptoms, tumor site, cancer stage, and first medical specialty consulted. Greater understanding of factors that influence delays and the individual impact of patient and provider delays on disease severity and prognosis would be useful to form effective policies and programs aimed at ensuring timely access to healthcare for children with cancer. Show more