Abstract Multiple comparison and multiple endpoint procedures are applied universally in a broad array of experimental settings. In confirmatory clinical trials of candidate drug and vaccine products the interest is in controlling the family-wise error rate (FWER) at a specified level α. Gaining popularity in many other discovery settings is an interest in maintaining the false discovery rate (FDR) as an attractive alternative to strict FWER control. Yosef Hochberg made impactful contributions to both FWER methods (Hochberg, 1988) and FDR methods (Benjamini and Hochberg, 1995) which are widely used in biopharmaceutical applications. When one or more of the hypotheses being tested is based on categorical data, it is possible to increase the power of FWER and FDR controlling procedures. This talk will trace the development of multiple comparison procedures for categorical data, starting with a proposal by Mantel (1980), and continuing to the development of fully discrete FDR controlling procedures. Special attention will be given to Hochberg’s contributions. The situation with multiple correlated endpoints will also be discussed. Simulations and theoretical arguments demonstrate the clear power advantages of multiplicity procedures that take proper accounting of the discreteness in the data. 3
Overview Yosef Hochberg made impactful contributions to both FWER methods and FDR methods which are widely used in biopharmaceutical applications. With discrete data it is possible to increase the power of FWER and FDR controlling procedures. This talk will trace the development of multiple comparison procedures for categorical data from early FWER procedures to fully discrete FDR controlling procedures. Special attention will be given to Hochberg’s contributions. The situation with multiple correlated endpoints will also be discussed. Simulations and theoretical arguments demonstrate the clear power advantages of multiplicity procedures that take proper accounting of the discreteness in the data. 4
Outline 1.Rodent carcinogenicity study circa 1980 2.Tests based on P min 3.Discrete Bonferroni method 4.Discrete Hochberg stepwise method 5.Non-independent hypotheses 6.Discrete FDR methods 7.Concluding remarks 5
Summary of Statistical Results From a Long-Term Carcinogenicity Study in Male Mice 6 Trend P-value is reported 1-tailed using exact permutational distribution. N indicates 1-tailed P-value for negative trend.
Multiplicity of Statistical Tests Liver, hepatocellular carcinoma was only 1 of K=15 tumor sites encountered. P (1) =0.0342 was the most extreme individual trend P-value. Interest is in the likelihood of observing P (1) =0.0342 as the most extreme P-value among the K=15 in this study. Need to consider the discrete nature of the data since several tumor sites may not be able to achieve significance levels of P (1).
Hochberg: Probability of Falsely Rejecting 1 or More True Hypotheses for Increasing Numbers Hypotheses Number of Hypotheses
Nucleotide Changes in cDNA Transcripts (Tarone, 1990) Ordered Nucleotide 1-Sided P-Value Hochberg Adj. P Hochberg Discrete Adj. P 11/108/110.00580.05220.0097 21/113/90.21670.81820.6184 32/114/100.26780.8182 41/103/100.29100.8182 52/92/80.66470.8182 62/112/100.66920.8182 72/9 0.71180.8182 82/9 0.71180.8182 93/82/70.8182
Non-independent Hypotheses Accounting for a known structure can improve the power of the testing procedure. Heyse and Rom (1988) proposed a multivariate permutation test for the rodent carcinogenicity experiment. Westfall and Young (1989, 1993) developed broader resampling approaches which have become the standard application (PROC MULTTEST). Possible to construct exact null distribution for discrete test statistics.
Illustration: Multiresponse representation of tumor data Control (X=0) Treated (X=1)Total Tumor Site A Only167 Tumor Site B Only303 Tumor Sites A&B123 No Tumor454287 Number on Study50 100 Site A: S A = 8, E(S A ) = 5 Site B: S B = 2, E(S B ) = 3
Rejection regions based on bivariate distribution of scores S A =6S A =7S A =8S A =9S A =10 --- AS B =3 --- AS B =4 --- AS B =5 BBBAB S B =6 Modified Bonferroni S A =6S A =7S A =8S A =9S A =10 --- AS B =3 --- AS B =4 --- AS B =5 BBAB S B =6 Hochberg
Return to Rodent Carcinogenicity Study MethodAdjusted P-value Adjust Extreme K=150.4067 Mantel (K*=9)0.2689 Mantel et al. (Discrete)0.2352 Heyse and Rom (Permutation)0.2363
False Discovery Rate (FDR) Almost all multiplicity considerations in clinical trial applications are designed to control the Family Wise Error Rate (FWER). Benjamini and Hochberg (1995) argued that in certain settings, requiring control of the FWER is often too conservative. They suggested controlling the “False Discovery Rate” (FDR) as a more powerful alternative. Accounting for the categorical endpoints can further improve the power of FDR (and FWER) methods.
Properties of FDR Control The B&H sequential procedure controls the FDR at FDR < FWER and equality holds if K=K 0. The Hochberg (1988) stepwise procedure compares while the FDR procedure compares FDR is potentially more powerful than FWER controlling procedures. for independent hypotheses.
Example: Genetic Variants of HIV Gilbert (2005) compared the mutation rates at 118 positions in HIV amino-acid sequences of 73 patients with subtype C to 73 patients with subtype B. The B-H FDR procedure identified 12 significant positions. The Tarone modified FDR procedure reduced the dimensionality to 25 and identified 15 significant positions. The fully discrete FDR identified 20 significant positions.
Recent Developments Using mid P-values Heller and Gur (2012) proposed using the B&H method on the mid P- values to reduce the conservatism with discrete data. Also developed a novel step-down procedure for discrete data. Simulations showed that the fully discrete adjustment method controlled the FDR and was most powerful among the tests considered. Example: the 27 most extreme signals from post marketing surveillance of spontaneous adverse experiences was evaluated. –B&H supported 22 signals –B&H applied to mid P supported 25 signals –Fully discrete B&H supported all 27 signals
Simulation Study for Independent Hypotheses A simulation study was conducted to evaluate the statistical properties of the FDR controlling methods for discrete data using Fisher’s Exact Test. Simulation parameters –Number of Hypotheses: K = 5, 10, 15, 20 –Varying numbers of false hypotheses (K-K 0 ) –Background rates chosen randomly from U(.01,.5) –Odds Ratios for Effect Size: OR = 1.5, 2, 2.5, 3 –Sample sizes: N = 10, 25, 50, 100 – = 0.05 1-Tailed
Rate of Rejecting True Hypotheses When All Hypotheses Are True (K 0 =K) 34
Rate of Rejecting True Hypotheses When Some Hypotheses Are False (K 0
"name": "Rate of Rejecting True Hypotheses When Some Hypotheses Are False (K 0
Concluding Remarks Understanding and evaluating multiplicity has been a critically important element in biopharmaceutical statistical applications. Multiplicity issues arise throughout the drug and vaccine development process from discovery, through clinical development, and into the post approval periods. Yosef Hochberg is to be commended for his important contributions. Hochberg’s methods for both FWER and FDR control can be applied in setting with discrete data. Thank you!!
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