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Incorrect Inferences (incorrect + inference)
Selected AbstractsZero tolerance ecology: improving ecological inference by modelling the source of zero observationsECOLOGY LETTERS, Issue 11 2005Tara G. Martin Abstract A common feature of ecological data sets is their tendency to contain many zero values. Statistical inference based on such data are likely to be inefficient or wrong unless careful thought is given to how these zeros arose and how best to model them. In this paper, we propose a framework for understanding how zero-inflated data sets originate and deciding how best to model them. We define and classify the different kinds of zeros that occur in ecological data and describe how they arise: either from ,true zero' or ,false zero' observations. After reviewing recent developments in modelling zero-inflated data sets, we use practical examples to demonstrate how failing to account for the source of zero inflation can reduce our ability to detect relationships in ecological data and at worst lead to incorrect inference. The adoption of methods that explicitly model the sources of zero observations will sharpen insights and improve the robustness of ecological analyses. [source] "What exactly are you inferring?"ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2008A closer look at hypothesis testing Abstract This critical review describes the confused application of significance tests in environmental toxicology and chemistry that often produces incorrect inferences and indefensible regulatory decisions. Following a brief review of statistical testing theory, nine recommendations are put forward. The first is that confidence intervals be used instead of hypothesis tests whenever possible. The remaining recommendations are relevant if hypothesis tests are used. They are as follows: Define and justify Type I and II error rates a priori; set and justify an effect size a priori; do not confuse p(E | H0) and p(H0 | E); design tests permitting Positive Predictive Value estimation; publish negative results; estimate a priori, not post hoc, power; as warranted by study goals, favor null hypotheses that are not conventional nil hypotheses; and avoid definitive inferences from isolated tests. [source] Multilevel models for estimating incremental net benefits in multinational studiesHEALTH ECONOMICS, Issue 8 2007Richard Grieve Abstract Multilevel models (MLMs) have been recommended for estimating incremental net benefits (INBs) in multicentre cost-effectiveness analysis (CEA). However, these models have assumed that the INBs are exchangeable and that there is a common variance across all centres. This paper examines the plausibility of these assumptions by comparing various MLMs for estimating the mean INB in a multinational CEA. The results showed that the MLMs that assumed the INBs were exchangeable and had a common variance led to incorrect inferences. The MLMs that included covariates to allow for systematic differences across the centres, and estimated different variances in each centre, made more plausible assumptions, fitted the data better and led to more appropriate inferences. We conclude that the validity of assumptions underlying MLMs used in CEA need to be critically evaluated before reliable conclusions can be drawn. Copyright © 2006 John Wiley & Sons, Ltd. [source] Using multilevel models for assessing the variability of multinational resource use and cost dataHEALTH ECONOMICS, Issue 2 2005Richard Grieve Abstract Multinational economic evaluations often calculate a single measure of cost-effectiveness using cost data pooled across several countries. To assess the validity of pooling international cost data the reasons for cost variation across countries need to be assessed. Previously, ordinary least-squares (OLS) regression models have been used to identify factors associated with variability in resource use and total costs. However, multilevel models (MLMs), which accommodate the hierarchical structure of the data, may be more appropriate. This paper compares these different techniques using a multinational dataset comprising case-mix, resource use and cost data on 1300 stroke admissions from 13 centres in 11 European countries. OLS and MLMs were used to estimate the effect of patient and centre-level covariates on the total length of hospital stay (LOS) and total cost. MLMs with normal and gamma distributions for the data within centres were compared. The results from the OLS model showed that both patient and centre-level covariates were associated with LOS and total cost. The estimates from the MLMs showed that none of the centre-level characteristics were associated with LOS, and the level of spending on health was the centre-level variable most highly associated with total cost. We conclude that using OLS models for assessing international variation can lead to incorrect inferences, and that MLMs are more appropriate for assessing why resource use and costs vary across centres. Copyright © 2004 John Wiley & Sons, Ltd. [source] The Joint Democracy,Dyadic Conflict Nexus: A Simultaneous Equations ModelINTERNATIONAL STUDIES QUARTERLY, Issue 3 2003Rafael Reuveny Many statistical studies in international relations investigate the claim that democracies do not fight one another. Virtually all of these studies employ a single-equation design, where the dependent variable measures the presence or absence of a dyadic militarized interstate dispute (MID). A separate group of studies argues that conflict affects democracy and that its effect could be positive or negative. By and large, these two bodies of literature have not incorporated one another's insights. We argue that democracy and dyadic conflict affect each other significantly and that statistical models that ignore the reciprocal nature of these effects may make incorrect inferences. To test this argument, we develop a simultaneous equations model of democracy and dyadic conflict. Our sample includes all the politically relevant dyads from 1950 to 1992. We find that dyadic military disputes reduce joint democracy and joint democracy reduces the probability of MIDs. Compared with the single-equation estimates in the literature, the absolute effect of joint democracy in our paper is smaller while in relative terms, the effect is similar in size. The effect of joint democracy on MID involvement is considerably smaller for noncontiguous countries than for contiguous ones. The effects of a number of control variables in the MID equation are also found to differ from those reported previously in single- equation,based studies. [source] Corporate Value, Managerial Stockholdings and Investments of Japanese FirmsJOURNAL OF INTERNATIONAL FINANCIAL MANAGEMENT & ACCOUNTING, Issue 1 2006Carl R. Chen We use a simultaneous equation model which treats firm value, investments and management ownership as endogenous to the firm. Our results show a feedback relation between corporate value and management ownership, i.e., corporate value is positively impacted by management ownership, which in turn is positively impacted by corporate value. Corporate value also affects investments made by the firm. We also find that the effect of the main bank on corporate value is positive but only up to a certain point; then, it turns negative. Supporting the argument that keiretsu firms have lower agency cost, we find that firms belonging to a keiretsu have higher valuations during the sample period. Finally, we find that management ownership increases as the ownership of the main bank, ownership of institutional holders and cross-holdings decreases, suggesting a substitution effect among these monitoring forces. Our results indicate that ignoring the web of these relationships leads to incorrect inferences. [source] | ||||||||||