Inferring meta-covariates in classification

This paper develops an alternative method for gene selection that combines model based clustering and binary classification. By averaging the covariates within the clusters obtained from model based clustering, we define “meta-covariates” and use them to build a probit regression model, thereby selecting clusters of similarly behaving genes, aiding interpretation. This simultaneous learning task is accomplished by an EM algorithm that optimises a single likelihood function which rewards good performance at both classification and clustering. We explore the performance of our methodology on a well known leukaemia dataset and use the Gene Ontology to interpret our results

Oracle inequalities for multi-fold cross validation

We consider choosing an estimator or model from a given class by cross validation consisting of holding a nonneglible fraction of the observations out as a test set. We derive bounds that show that the risk of the resulting procedure is (up to a constant) smaller than the risk of an oracle plus an error which typically grows logarithmically with the number of estimators in the class. We extend the results to penalized cross validation in order to control unbounded loss functions. Applications include regression with squared and absolute deviation loss and classification under Tsybakov’s condition.Article / Letter to editorMathematisch Instituu

Multiple Testing Procedures: R multtest Package and Applications to Genomics

The Bioconductor R package multtest implements widely applicable resampling-based single-step and stepwise multiple testing procedures (MTP) for controlling a broad class of Type I error rates, in testing problems involving general data generating distributions (with arbitrary dependence structures among variables), null hypotheses, and test statistics. The current version of multtest provides MTPs for tests concerning means, differences in means, and regression parameters in linear and Cox proportional hazards models. Procedures are provided to control Type I error rates defined as tail probabilities for arbitrary functions of the numbers of false positives and rejected hypotheses. These error rates include tail probabilities for the number of false positives (generalized family-wise error rate, gFWER) and the proportion of false positives among the rejected hypotheses (TPPFP). Single-step and step-down common-cut-off (maxT) and common-quantile (minP) procedures, that take into account the joint distribution of the test statistics, are proposed to control the family-wise error rate (FWER), or chance of at least one Type I error. In addition, augmentation multiple testing procedures are provided to control the gFWER and TPPFP, based on any initial FWER-controlling procedure. The results of a multiple testing procedure can be summarized using rejection regions for the test statistics, confidence regions for the parameters of interest, or adjusted p-values. A key ingredient of our proposed MTPs is the test statistics null distribution (and estimator thereof) used to derive rejection regions and corresponding confidence regions and adjusted p-values. Both bootstrap and permutation estimators of the test statistics null distribution are available. The S4 class/method object-oriented programming approach was adopted to summarize the results of a MTP. The modular design of multtest allows interested users to readily extend the package\u27s functionality. Typical testing scenarios are illustrated by applying various MTPs implemented in multtest to the Acute Lymphoblastic Leukemia (ALL) dataset of Chiaretti et al. (2004), with the aim of identifying genes whose expression measures are associated with (possibly censored) biological and clinical outcomes

Multiple Testing. Part II. Step-Down Procedures for Control of the Family-Wise Error Rate

The present article proposes two step-down multiple testing procedures for asymptotic control of the family-wise error rate (FWER): the first procedure is based on maxima of test statistics (step-down maxT), while the second relies on minima of unadjusted p-values (step-down minP). A key feature of our approach is the test statistics null distribution (rather than data generating null distribution) used to derive cut-offs (i.e., rejection regions) for these test statistics and the resulting adjusted p-values. For general null hypotheses, corresponding to submodels for the data generating distribution, we identify an asymptotic domination condition for a null distribution under which the step-down maxT and minP procedures asymptotically control the Type I error rate, for arbitrary data generating distributions, without the need for conditions such as subset pivotality. Inspired by this general characterization of a null distribution, we then propose as an explicit null distribution the asymptotic distribution of the vector of null-value shifted and scaled test statistics. Step-down procedures based on consistent estimators of the null distribution are shown to also provide asymptotic control of the Type I error rate. A general bootstrap algorithm is supplied to conveniently obtain consistent estimators of the null distribution

Multiple Testing. Part I. Single-Step Procedures for Control of General Type I Error Rates

The present article proposes general single-step multiple testing procedures for controlling Type I error rates defined as arbitrary parameters of the distribution of the number of Type I errors, such as the generalized family-wise error rate. A key feature of our approach is the test statistics null distribution (rather than data generating null distribution) used to derive cut-offs (i.e., rejection regions) for these test statistics and the resulting adjusted p-values. For general null hypotheses, corresponding to submodels for the data generating distribution, we identify an asymptotic domination condition for a null distribution under which single-step common-quantile and common-cut-off procedures asymptotically control the Type I error rate, for arbitrary data generating distributions, without the need for conditions such as subset pivotality. Inspired by this general characterization of a null distribution, we then propose as an explicit null distribution the asymptotic distribution of the vector of null-value shifted and scaled test statistics. In the special case of family-wise error rate (FWER) control, our method yields the single-step minP and maxT procedures based on minima of unadjusted p-values and maxima of test statistics, respectively, with the important distinction in the choice of null distribution. Single-step procedures based on consistent estimators of the null distribution are shown to also provide asymptotic control of the Type I error rate. A general bootstrap algorithm is supplied to conveniently obtain consistent estimators of the null distribution. The special cases of t- and F-statistics are discussed in detail. The companion articles focus on step-down multiple testing procedures for control of the FWER (van der Laan et al., 2003a) and on augmentations of FWER-controlling methods to control error rates such as the generalized family-wise error rate and the proportion of false positives among the rejected hypotheses (van der Laan et al., 2003b). The proposed bootstrap multiple testing procedures are evaluated by a simulation study and applied to gene expression microarray data in the fourth article of the series (Pollard et al., 2004)

Multiple Testing. Part III. Procedures for Control of the Generalized Family-Wise Error Rate and Proportion of False Positives

The accompanying articles by Dudoit et al. (2003b) and van der Laan et al. (2003) provide single-step and step-down resampling-based multiple testing procedures that asymptotically control the family-wise error rate (FWER) for general null hypotheses and test statistics. The proposed procedures fundamentally differ from existing approaches in the choice of null distribution for deriving cut-offs for the test statistics and are shown to provide asymptotic control of the FWER under general data generating distributions, without the need for conditions such as subset pivotality. In this article, we show that any multiple testing procedure (asymptotically) controlling the FWER at level alpha can be augmented into: (i) a multiple testing procedure (asymptotically) controlling the generalized family-wise error rate (i.e., the probability, gFWER(k), of having more than k false positives) at level alpha and (ii) a multiple testing procedure (asymptotically) controlling the probability, PFP(q), that the proportion of false positives among the rejected hypotheses exceeds a user-supplied value q in (0,1) at level alpha. Existing procedures for control of the proportion of false positives typically rely on the assumption that the test statistics are independent, while our proposed augmentation procedures control the PFP and gFWER for general data generating distributions, with arbitrary dependence structures among variables. Applying our augmentation methods to step-down multiple testing procedures that asymptotically control the FWER at exact level alpha (van der Laan et al., 2003), yields multiple testing procedures that also asymptotically control the gFWER and PFP at exact level alpha. Finally, the adjusted p-values for the gFWER and PFP-controlling augmentation procedures are shown to be simple functions of the adjusted p-values for the original FWER-controlling procedure

Scaling Analysis of Affinity Propagation

We analyze and exploit some scaling properties of the Affinity Propagation (AP) clustering algorithm proposed by Frey and Dueck (2007). First we observe that a divide and conquer strategy, used on a large data set hierarchically reduces the complexity ${\cal O}(N^2)$ to ${\cal O}(N^{(h+2)/(h+1)})$, for a data-set of size $N$ and a depth $h$ of the hierarchical strategy. For a data-set embedded in a $d$-dimensional space, we show that this is obtained without notably damaging the precision except in dimension $d=2$. In fact, for $d$ larger than 2 the relative loss in precision scales like $N^{(2-d)/(h+1)d}$. Finally, under some conditions we observe that there is a value $s^*$ of the penalty coefficient, a free parameter used to fix the number of clusters, which separates a fragmentation phase (for $s<s^*$) from a coalescent one (for $s>s^*$) of the underlying hidden cluster structure. At this precise point holds a self-similarity property which can be exploited by the hierarchical strategy to actually locate its position. From this observation, a strategy based on \AP can be defined to find out how many clusters are present in a given dataset.Comment: 28 pages, 14 figures, Inria research repor

Multiple Testing Procedures and Applications to Genomics

This chapter proposes widely applicable resampling-based single-step and stepwise multiple testing procedures (MTP) for controlling a broad class of Type I error rates, in testing problems involving general data generating distributions (with arbitrary dependence structures among variables), null hypotheses, and test statistics (Dudoit and van der Laan, 2005; Dudoit et al., 2004a,b; van der Laan et al., 2004a,b; Pollard and van der Laan, 2004; Pollard et al., 2005). Procedures are provided to control Type I error rates defined as tail probabilities for arbitrary functions of the numbers of Type I errors, V_n, and rejected hypotheses, R_n. These error rates include: the generalized family-wise error rate, gFWER(k) = Pr(V_n \u3e k), or chance of at least (k+1) false positives (the special case k=0 corresponds to the usual family-wise error rate, FWER), and tail probabilities for the proportion of false positives among the rejected hypotheses, TPPFP(q) = Pr(V_n/R_n \u3e q). Single-step and step-down common-cut-off (maxT) and common-quantile (minP) procedures, that take into account the joint distribution of the test statistics, are proposed to control the FWER. In addition, augmentation multiple testing procedures are provided to control the gFWER and TPPFP, based on any initial FWER-controlling procedure. The results of a multiple testing procedure can be summarized using rejection regions for the test statistics, confidence regions for the parameters of interest, or adjusted p-values. A key ingredient of our proposed MTPs is the test statistics null distribution (and consistent bootstrap estimator thereof) used to derive rejection regions and corresponding confidence regions and adjusted p-values. This chapter illustrates an implementation in SAS (Version 9) of the bootstrap-based single-step maxT procedure and of the gFWER- and TPPFP-controlling augmentation procedures. These multiple testing procedures are applied to an HIV-1 sequence dataset to identify codon positions associated with viral replication capacity

A nonparametric framework for treatment effect modifier discovery in high dimensions

Heterogeneous treatment effects are driven by treatment effect modifiers, pre-treatment covariates that modify the effect of a treatment on an outcome. Current approaches for uncovering these variables are limited to low-dimensional data, data with weakly correlated covariates, or data generated according to parametric processes. We resolve these issues by developing a framework for defining model-agnostic treatment effect modifier variable importance parameters applicable to high-dimensional data with arbitrary correlation structure, deriving one-step, estimating equation and targeted maximum likelihood estimators of these parameters, and establishing these estimators' asymptotic properties. This framework is showcased by defining variable importance parameters for data-generating processes with continuous, binary, and time-to-event outcomes with binary treatments, and deriving accompanying multiply-robust and asymptotically linear estimators. Simulation experiments demonstrate that these estimators' asymptotic guarantees are approximately achieved in realistic sample sizes for observational and randomized studies alike. This framework is applied to gene expression data collected for a clinical trial assessing the effect of a monoclonal antibody therapy on disease-free survival in breast cancer patients. Genes predicted to have the greatest potential for treatment effect modification have previously been linked to breast cancer. An open-source R package implementing this methodology, unihtee, is made available on GitHub at https://github.com/insightsengineering/unihtee

Resampling-Based Multiple Hypothesis Testing with Applications to Genomics: New Developments in the R/Bioconductor Package multtest

The multtest package is a standard Bioconductor package containing a suite of functions useful for executing, summarizing, and displaying the results from a wide variety of multiple testing procedures (MTPs). In addition to many popular MTPs, the central methodological focus of the multtest package is the implementation of powerful joint multiple testing procedures. Joint MTPs are able to account for the dependencies between test statistics by effectively making use of (estimates of) the test statistics joint null distribution. To this end, two additional bootstrap-based estimates of the test statistics joint null distribution have been developed for use in the package. For asymptotically linear estimators involving single-parameter hypotheses (such as tests of means, regression parameters, and correlation parameters using t-statistics), a computationally efficient joint null distribution estimate based on influence curves is now also available. New MTPs implemented in multtest include marginal adaptive procedures for control of the false discovery rate (FDR) as well as empirical Bayes joint MTPs which can control any Type I error rate defined as a function of the numbers of false positives and true positives. Examples of such error rates include, among others, the family-wise error rate and the FDR. S4 methods are available for objects of the new class EBMTP, and particular attention has been given to reducing the need for repeated resampling between function calls