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Median tests for censored survival data; a contingency table approach.

ABSTRACT: The median failure time is often utilized to summarize survival data because it has a more straightforward interpretation for investigators in practice than the popular hazard function. However, existing methods for comparing median failure times for censored survival data either require estimation of the probability density function or involve complicated formulas to calculate the variance of the estimates. In this article, we modify a K-sample median test for censored survival data (Brookmeyer and Crowley, 1982, Journal of the American Statistical Association 77, 433-440) through a simple contingency table approach where each cell counts the number of observations in each sample that are greater than the pooled median or vice versa. Under censoring, this approach would generate noninteger entries for the cells in the contingency table. We propose to construct a weighted asymptotic test statistic that aggregates dependent ?(2)-statistics formed at the nearest integer points to the original noninteger entries. We show that this statistic follows approximately a ?(2)-distribution with k-1 degrees of freedom. For a small sample case, we propose a test statistic based on combined p-values from Fisher's exact tests, which follows a ?(2)-distribution with 2 degrees of freedom. Simulation studies are performed to show that the proposed method provides reasonable type I error probabilities and powers. The proposed method is illustrated with two real datasets from phase III breast cancer clinical trials.

SUBMITTER: Tang S

PROVIDER: S-EPMC4281497 | biostudies-literature | 2012 Sep

REPOSITORIES: biostudies-literature

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Median tests for censored survival data; a contingency table approach.

Tang Shaowu S Jeong Jong-Hyeon JH

Biometrics 20120901 3

The median failure time is often utilized to summarize survival data because it has a more straightforward interpretation for investigators in practice than the popular hazard function. However, existing methods for comparing median failure times for censored survival data either require estimation of the probability density function or involve complicated formulas to calculate the variance of the estimates. In this article, we modify a K-sample median test for censored survival data (Brookmeyer ...[more]

PMID: 23189327

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Project description:OBJECTIVES:We tested the hypothesis that a C-reactive protein and ferritin-based systemic inflammation contingency table can track mortality risk in pediatric severe sepsis. DESIGN:Prospective cohort study. SETTING:Tertiary PICU. PATIENTS:Children with 100 separate admission episodes of severe sepsis were enrolled. INTERVENTIONS:Blood samples were attained on day 2 of sepsis and bi-weekly for biomarker batch analysis. A 2?×?2 contingency table using C-reactive protein and ferritin thresholds was developed. MEASUREMENTS AND MAIN RESULTS:A C-reactive protein of 4.08?mg/dL and a ferritin of 1,980?ng/mL were found to be optimal cutoffs for outcome prediction at first sampling (n = 100) using the Youden index. PICU mortality was increased in the "high-risk" C-reactive protein greater than or equal to 4.08?mg/dL and ferritin greater than or equal to 1,980?ng/mL category (6/13 [46.15%]) compared with the "intermediate-risk" C-reactive protein greater than or equal to 4.08?mg/dL and ferritin less than 1,980?ng/mL or C-reactive protein less than 4.08?mg/dL and ferritin greater than or equal to 1,980?ng/mL categories (2/43 [4.65%]), and the "low-risk" C-reactive protein less than 4.08?mg/dL and ferritin less than 1,980?ng/mL category (0/44 [0%]) (odds ratio, 36.43 [95% CI, 6.16-215.21]). The high-risk category was also associated with the development of immunoparalysis (odds ratio, 4.47 [95% CI, 1.34-14.96]) and macrophage activation syndrome (odds ratio, 24.20 [95% CI, 5.50-106.54]). Sixty-three children underwent sequential blood sampling; those who were initially in the low-risk category (n = 24) and those who subsequently migrated (n = 19) to the low-risk category all survived, whereas those who remained in the "at-risk" categories had increased mortality (7/20 [35%]; p < 0.05). CONCLUSIONS:A C-reactive protein- and ferritin-based contingency table effectively assessed mortality risk. Reduction in systemic inflammation below a combined threshold C-reactive protein of 4.08?mg/dL and ferritin of 1,980?ng/mL appeared to be a desired response in children with severe sepsis.

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Median tests for censored survival data; a contingency table approach.

Publications

Median tests for censored survival data; a contingency table approach.

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