Reflections on Accuracy

The difference between test accuracy and predictive accuracy is presented and defined. The failure to distinguish between these two types of measures is shown to have led to a misguided debate over the interpretation of prevalence estimates. The distinction between test accuracy defined as sensitivity and specificity, and predictive accuracy defined as positive and negative predictive value is shown to reflect the choice of the denominator used to calculate true positive, false positive, false negative, and true negative rates. It is further shown that any instrument will tend to overestimate prevalence in low base rate populations and underestimate it in those populations where prevalence is high. The implications of these observations are then discussed in terms of the need to define diagnostic thresholds that have clinical and policy relevance.     

Current Challenges of North/South Relations in Gay-Lesbian and Queer Studies

ABSTRACT

The article assesses and analyzes different dimensions of the current configuration of North/South dialogues within gay-lesbian and queer studies, with particular attention to the interrelations between the United States and South America. It looks into how gay-lesbian and queer studies relate to the global division and hierarchy of intellectual labor traditionally embedded in academic practices, and it asks whether the scope of its radical program includes a revision of unequal academic dynamics. Its concerns are both ethical and epistemological, as they speak not only to the moral and political dimensions of academic practice, but also to how these modes affect the knowledge produced in the United States and in South America today. By offering a view from the South conversant with South American as well as Northern production, we hope to contribute to both local and international debates regarding the present and future of the field.     

On the location of new facilities for chain expansion under delivered pricing

We study the problem of locating new facilities for one expanding chain which competes for demand in spatially separated markets where all competing chains use delivered pricing. A new network location model is formulated for profit maximization of the expanding chain assuming that equilibrium prices are set in each market. The cannibalization effect caused by the entrance of the new facilities is integrated in the objective function as a cost to be paid by the expanding chain to the cannibalized facilities. It is shown that the profit of the chain is maximized by locating the new facilities in a set of points which are nodes or iso-marginal delivered cost points (points on the network from which the marginal delivered cost equals the minimum marginal delivered cost from the existing facilities owned by the expanding chain). Then the location problem is reduced to a discrete optimization problem which is formulated as a mixed integer linear program. A sensitivity analysis respect to both the number of new facilities and the cannibalization cost is shown by using an illustrative example with data of the region of Murcia (Spain). Some conclusions are presented.     

Records Properties of Non Stationary Time Series

This article proposes an asymptotic expansion for the Studentized linear discriminant function using two-step monotone missing samples under multivariate normality. The asymptotic expansions related to discriminant function have been obtained for complete data under multivariate normality. The result derived by Anderson (1973 Anderson , T. W. ( 1973 ). An asymptotic expansion of the distribution of the Studentized classification statistic W . The Annals of Statistics 1 : 964 – 972 .[Crossref], [Web of Science ®] , [Google Scholar]) plays an important role in deciding the cut-off point that controls the probabilities of misclassification. This article provides an extension of the result derived by Anderson (1973 Anderson , T. W. ( 1973 ). An asymptotic expansion of the distribution of the Studentized classification statistic W . The Annals of Statistics 1 : 964 – 972 .[Crossref], [Web of Science ®] , [Google Scholar]) in the case of two-step monotone missing samples under multivariate normality. Finally, numerical evaluations by Monte Carlo simulations were also presented.     

Different Factors for Different Causes: Analysis of the Spatial Aggregations of Fire Ignitions in Catalonia (Spain)

The present study analyzes the effects of different socioeconomic factors on the frequency of fire ignition occurrence, according to different original causes. The data include a set of documented ignition points in the region of Catalonia for the period 1995–2008. The analysis focused on the spatial aggregation patterns of the ignitions for each specific ignition cause. The point‐based data on ignitions were interpolated into municipality‐level information using kernel methods as the basis for defining five ignition density levels. Afterwards, the combination of socioeconomic factors influencing the ignition density levels of the municipalities was analyzed for each documented cause of ignition using a principal component analysis. The obtained results confirmed the idea that both the spatial aggregation patterns of fire ignitions and the factors defining their occurrence were specific for each of the causes of ignition. Intentional fires and those of unknown origin were found to have similar spatial aggregation patterns, and the presence of high ignition density areas was related to high population and high unemployment rates. Additionally, it was found that fires originated from forest work, agricultural activities, pasture burning, and lightning had a very specific behavior on their own, differing from the similarities found on the spatial aggregation of ignitions originated from smokers, electric lines, machinery, campfires, and those of intentional or unknown origin.     

Vector autoregressive models with measurement errors for testing Granger causality

This paper develops a method for estimating the parameters of a vector autoregression (VAR) observed in white noise. The estimation method assumes that the noise variance matrix is known and does not require any iterative process. This study provides consistent estimators and the asymptotic distribution of the parameters required for conducting tests of Granger causality. Methods in the existing statistical literature cannot be used for testing Granger causality, since under the null hypothesis the model becomes unidentifiable. Measurement error effects on parameter estimates were evaluated by using computational simulations. The results suggest that the proposed approach produces empirical false positive rates close to the adopted nominal level (even for small samples) and has a satisfactory performance around the null hypothesis. The applicability and usefulness of the proposed approach are illustrated using a functional magnetic resonance imaging dataset.     

A Comment on the Utility of Prevalence Estimates of Pathological Gambling

The case is presented that researchers interested in policy aimed at treating the pathological gambler need to shift focus to improving the utility of prevalence estimates. It is argued that researchers supplement prevalence estimates with practical and well-defined measures of severity and other predictors and correlates of help-seeking. The dimension of severity is emphasized as one means of providing estimates that are relevant to policy makers when placed in the context of additional measures that improve their meaning and utility. Estimates may then be partitioned along these dimensions to ascertain the proportion of gamblers most likely to need or seek treatment for gambling-related disorders. The recommendations provided are subject to a number of possible objections and are presented in the interest of stimulating further discussion such as the distinction between symptom assessment and the measurement of severity.     

What Men Who Have Sex With Men in Peru Want in Internet-Based Sexual Health Information

We aimed to gather information among gay men regarding their preferences for online sexual health information; 1,160 Peruvian MSM, 18 years or older, completed an online survey hosted on www.tunexo.org. The mean age was 26.8 years. Around 90% had post–high school education. The self-reported HIV prevalence was 12.3%. The acceptability of sexual health content was greater in the most highly educated group. The highest rated topics and services of interest were those related to improving sexual and mental health. The least educated group was significantly more interested in “getting prevention messages on mobiles” compared to men with the highest level of education (71% vs. 52%; p < 0.001). Men’s sexual health was of more interest to the 30–39-year-old group compared to the 18–24-year-old one (97% vs. 87%; p = 0.005). Future Web-based interventions related to sexual health among targeted groups of MSM in Peru can be tailored to meet their preferences.     

Statistical analysis of controlled calibration model with replicates

In this work, we generalize the controlled calibration model by assuming replication on both variables. Likelihood-based methodology is used to estimate the model parameters and the Fisher information matrix is used to construct confidence intervals for the unknown value of the regressor variable. Further, we study the local influence diagnostic method which is based on the conditional expectation of the complete-data log-likelihood function related to the EM algorithm. Some useful perturbation schemes are discussed. A simulation study is carried out to assess the effect of the measurement error on the estimation of the parameter of interest. This new approach is illustrated with a real data set.     

A Test of the False Positive Bias Hypothesis

An evaluation of the hypothesis that adolescent gamblers are biased toward the production of false positive responses proposed by Derevensky et al. was tested. The results of secondary analysis of available data supported the hypothesis for items on the South Oaks Gambling Screen and items from the DSM-IV screening instrument. The conclusions were presented as tentative in view of the modest sizes of the observed effects. A number of limitations to the analysis are also described.