Combining effect size estimates in meta-analysis with repeated measures and independent-groups designs.

When a meta-analysis on results from experimental studies is conducted, differences in the study design must be taken into consideration. A method for combining results across independent-groups and repeated measures designs is described, and the conditions under which such an analysis is appropriate are discussed. Combining results across designs requires that (a) all effect sizes be transformed into a common metric, (b) effect sizes from each design estimate the same treatment effect, and (c) meta-analysis procedures use design-specific estimates of sampling variance to reflect the precision of the effect size estimates. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Alternative procedures for testing regression slope homogeneity when group error variances are unequal.

The test for regression slope homogeneity across groups (e.g., sex, race, and treatments) is used in such varied settings as the analysis of covariance, the study of aptitude by treatment interactions, and bias detection in differential prediction research. The accuracy of this test requires the seldom-considered assumption of equality of within-group error variances. This research studies the effect of violating that assumption on the power of the F test for regression slope equality and finds that the test may be substantially affected when sample sizes are equal and severely affected when sample sizes are unequal. Alternative procedures based on R. A. Alexander's (see record 1994-39680-001) normalized-t approximation, G. S. James's (1951) second-order approximation, the Welch-Aspin approximation, and the chi-square test are described and evaluated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bias in meta-analytic estimates of the absolute efficacy of psychotherapy.

Meta-analytic estimates of the absolute efficacy of psychotherapy indicate an effect size of approximately 0.80. However, various biases in primary and meta-analytic studies may have influenced this estimate. This study examines 4 nonsystematic biases that increase error variance (i.e., nonrandomized designs, methodological deficiencies, failure to use the study as the unit of analysis, and violations of homogeneity), 4 underestimation biases that primarily concern psychometric issues (i.e., unreliability of outcome measures, failure to report nonsignificant effect sizes, nonoptimal composite outcome measures, and nonstandardized outcome measures), and 8 overestimation biases (i.e., excluding nonsignificant effects from calculations of effect size estimates, failure to adjust for small sample bias, failure to separate studies using single-group pre-post designs vs. control group designs, using unweighted average effect sizes, analyzing biased partial samples that reflect treatment dropout and research attrition, researcher allegiance bias, publication bias, and wait-list control group bias). Wherever possible, evidence regarding the magnitude of these biases is presented, and methods for addressing these biases separately and collectively are discussed. Implications of the meta-analytic evidence on psychotherapy for the effect sizes of other psychological interventions are also considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intraclass correlation estimates in a school-based smoking prevention study. Outcome and mediating variables, by sex and ethnicity

Most school-based smoking prevention studies employ designs in which schools or classrooms are assigned to different treatment conditions while observations are made on individual students. This design requires that the treatment effect be assessed against the between-school variance. However, the between-school variance is usually larger than the variance that would be obtained if students were individually randomized to different conditions. Consequently, the power of the test for a treatment effect is reduced, and it becomes difficult to detect important treatment effects. To assess the potential loss of power or to calculate appropriate sample sizes, investigators need good estimates of the intraclass correlations for the variables of interest. The authors calculated intraclass correlations for some common outcome variables in a school-based smoking prevention study, using a three-level model-i.e., students nested within classrooms and classrooms nested within schools. The authors present the intraclass correlation estimates for the entire data set, as well as separately by sex and ethnicity. They also illustrate the use of these estimates in the planning of future studies.     

Validation and statistical power: Implications for applied research.

Comments that criterion-related validity studies are often not technically feasible because sample sizes are inadequate for necessary statistical power (e.g., .90). Effect sizes are frequently overestimated because of a failure to consider the combined effects of range restriction and criterion unreliability, both of which attenuate validity coefficients. Restricted validities must therefore be estimated by applying appropriate correction formulas. In this study the corrections are made for the multiple prediction case. Required sample sizes, determined using the univariate power model, are presented for a range of unit-weighted predictors, for varying degrees of restriction, and for power levels of .50 and .90. The advantage of multiple predictors is shown by comparing their required sample size to that of the best single predictor. For a given power, effect size is clearly the major determinant of required sample size. Implications for applied research are discussed. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Joan McKay versus John McKay: Do gender stereotypes bias evaluations?

Examines research using a classic, influential experiment conducted by Goldberg (1968), showing that women were likely to rate male authors (e.g., John T. McKay) more favorably than female authors (e.g., Joan T. McKay) of identical articles. Although replications of this study have been inconclusive, Goldberg's research is still frequently cited as demonstrating an evaluative bias against women. A quantitative meta-analysis of research using Goldberg's experimental paradigm shows that the average difference between ratings of men and women is negligible. Furthermore, although the effect sizes are not homogeneous, the difference remains negligible when other factors such as sex of subject or year of publication are taken into consideration. Several explanations for the heterogeneity of effect sizes and the inconsistency of findings are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Psychosis as a risk factor for violence to others: A meta-analysis.

The potential association between psychosis and violence to others has long been debated. Past research findings are mixed and appear to depend on numerous potential moderators. As such, the authors conducted a quantitative review (meta-analysis) of research on the association between psychosis and violence. A total of 885 effect sizes (odds ratios) were calculated or estimated from 204 studies on the basis of 166 independent data sets. The central tendency (median) of the effect sizes indicated that psychosis was significantly associated with a 49%–68% increase in the odds of violence. However, there was substantial dispersion among effect sizes. Moderation analyses indicated that the dispersion was attributable in part to methodological factors, such as study design (e.g., community vs. institutional samples), definition and measurement of psychosis (e.g., diagnostic vs. symptom-level measurement, type of symptom), and comparison group (e.g., psychosis compared with externalizing vs. internalizing vs. no mental disorder). The authors discuss these findings in light of potential causal models of the association between psychosis and violence, the role of psychosis in violence risk assessment and management, and recommendations for future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anchoring on the "here" and "now" in time and distance judgments.

Time and distance estimates were elicited with either unit-based (e.g., "How many days until...") or end-based (e.g., "On what date...") questions. For intervals of uncertain extent, unit-based estimates were consistently lower than were the corresponding end-based estimates. The observed patterns are consistent with an anchoring and adjustment process: When people generate unit-based estimates of uncertain dates or distances, they may anchor on the "here" or "now" and adjust incrementally by the unit; such adjustment, however, is often insufficient and yields systematic underestimation. Although this anchoring and adjustment cannot be directly observed, consistent with the hypothesized process, reliance on larger units yielded higher estimates and warning about insufficient adjustment reduced the effect. Implications for research on anchoring, the planning fallacy, and everyday judgment are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Quantitative imaging of bromine-76 and yttrium-86 with PET: a method for the removal of spurious activity introduced by cascade gamma rays

Positron Emission Tomography of bromine-76 and yttrium-86 results in the detection of coincident events that are not strictly associated with annihilation photon pairs. Instead, these coincidences occur because prompt gamma rays emitted by these nuclides result in cascades of photons that are emitted within the timing window of the PET scanner. Pairs of detected photons from these cascades are not angularly correlated and therefore contain little information regarding the location of their source. Furthermore, these coincidences are not removed by correction procedures (e.g., randoms, scatter) routinely applied to PET data. If left uncorrected, the cascade coincidences will result in spurious apparent activity within the PET images. A correction, applied within projection space, that removes the cascade coincidence signal from septa-in (i.e., two-dimensional) datasets is proposed and tested on phantom data.     

Estimating net joint torques from kinesiological data using optimal linear system theory

Net joint torques (NJT) are frequently computed to provide insights into the motor control of dynamic biomechanical systems. An inverse dynamics approach is almost always used, whereby the NJT are computed from 1) kinematic measurements (e.g., position of the segments), 2) kinetic measurements (e.g., ground reaction forces) that are, in effect, constraints defining unmeasured kinematic quantities based on a dynamic segmental model, and 3) numerical differentiation of the measured kinematics to estimate velocities and accelerations that are, in effect, additional constraints. Due to errors in the measurements, the segmental model, and the differentiation process, estimated NJT rarely produce the observed movement in a forward simulation when the dynamics of the segmental system are inherently unstable (e.g., human walking). Forward dynamic simulations are, however, essential to studies of muscle coordination. We have developed an alternative approach, using the linear quadratic follower (LQF) algorithm, which computes the NJT such that a stable simulation of the observed movement is produced and the measurements are replicated as well as possible. The LQF algorithm does not employ constraints depending on explicit differentiation of the kinematic data, but rather employs those depending on specification of a cost function, based on quantitative assumptions about data confidence. We illustrate the usefulness of the LQF approach by using it to estimate NJT exerted by standing humans perturbed by support-surface movements. We show that unless the number of kinematic and force variables recorded is sufficiently high, the confidence that can be placed in the estimates of the NJT, obtained by any method (e.g., LQF, or the inverse dynamics approach), may be unsatisfactorily low.     

Risk-adjusted cancer-incidence rates (United States)

A risk-adjusted method is proposed for estimating cancer incidence rates from data collected by the Surveillance, Epidemiology, and End Results (SEER) program of the US National Cancer Institute. Unlike the conventional incidence-rate estimates reported by SEER, this method considers only the first primary cancer, and adjusts for population-based cancer prevalence, as well as for surgical procedures which remove an individual from risk of developing a given cancer. Thus, risk-adjusted incidence-rates more accurately reflect the average cancer risk for individuals in the cancer-free, at-risk population. The results of the analysis indicate that, in general, incidence-rate estimates are fairly similar between the conventional and risk-adjusted methods. However, this is not the case for certain cancer sites which may have: (i) a high number of subsequent primary cancers (e.g., melanomas-skin); (ii) a high cancer prevalence proportion (e.g., prostate cancer); (iii) a high number of subsequent primary cancers and prevalence proportion (e.g., female breast); or (iv) a high prevalence of removal of the organ in question (e.g., cervical and uterine cancers). For example, by applying the risk-adjusted incidence method for in situ and invasive cervical cancer, we found that in the period 1990-92 the age-adjusted incidence-rate estimate increased from 57.8 to 66.3 (15 percent) per 100,000 person-years; the greatest increase in the incidence-rate estimate occurred for women aged 65 to 69 years, from 40.1 to 63.2 (58 percent) per 100,000 person-years; and the lifetime risk of developing cervical cancer increased from 4.6 (1 in 22) to 5.5 (1 in 18) percent.     

Action embellishment: An intention bias in the perception of success.

Na?ve theories of behavior hold that actions are caused by an agent's intentions, and the subsequent success of an action is measured by the satisfaction of those intentions. However, when an action is not as successful as intended, the expected causal link between intention and action may distort perception of the action itself. Four studies found evidence of an intention bias in perceptions of action. Actors perceived actions to be more successful when given a prior choice (e.g., choose between 2 words to type) and also when they felt greater motivation for the action (e.g., hitting pictures of disliked people). When the intent was to fail (e.g., singing poorly), choice led to worse estimates of performance. A final experiment suggested that intention bias works independent from self-enhancement motives. In observing another actor hit pictures of Hillary Clinton and Barack Obama, shots were distorted to match the actor's intentions, even when it opposed personal wishes. Together these studies indicate that judgments of action may be automatically distorted and that these inferences arise from the expected consistency between intention and action in agency. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

A meta-analytic review of depression prevention programs for children and adolescents: Factors that predict magnitude of intervention effects.

In this meta-analytic review, the authors summarized the effects of depression prevention programs for youth as well as investigated participant, intervention, provider, and research design features associated with larger effects. They identified 47 trials that evaluated 32 prevention programs, producing 60 intervention effect sizes. The average effect for depressive symptoms from pre-to-posttreatment (r = .15) and pretreatment to-follow-up (r = .11) were small, but 13 (41%) prevention programs produced significant reductions in depressive symptoms and 4 (13%) produced significant reductions in risk for future depressive disorder onset relative to control groups. Larger effects emerged for programs targeting high-risk individuals, samples with more females, samples with older adolescents, programs with a shorter duration and with homework assignments, and programs delivered by professional interventionists. Intervention content (e.g., a focus on problem-solving training or reducing negative cognitions) and design features (e.g., use of random assignment and structured interviews) were unrelated to effect sizes. Results suggest that depression prevention efforts produce a higher yield if they incorporate factors associated with larger intervention effects (e.g., selective programs with a shorter duration that include homework). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Meta-analysis methodology for combining non-parametric sibpair linkage results: genetic homogeneity and identical markers

Meta-analysis methodology is developed for combining sibpair linkage results across multiple studies employing different study designs, some employing quantitative traits (e.g., blood pressure) and some employing qualitative traits (e.g., clinical hypertension), under the assumption that the underlying (disease) trait loci are the same. Pooling results based on three commonly used sibpair methods is considered: the affected sibpair method for dichotomous traits and, for quantitative traits, the Haseman-Elston regression method and the Risch-Zhang extremely discordant sibpair method. The proportion of genes shared identical by descent (IBD) by a sibpair of certain trait outcomes is chosen as a common effect to be pooled across studies. Variation in the observed IBD proportions among individual studies is modeled using a random effects model. A heterogeneity test is provided to assess the variability among individual studies. When results from all three types of studies are available, we derive pooled estimates of IBD proportions both for sibpairs with extremely concordant trait values and for sibpairs with extremely discordant trait values, and construct a combined test of linkage based on the difference of the two estimates. Simulation studies demonstrate the need for and the advantage of meta-analysis of linkage results. We also present some guidelines for reporting linkage studies bearing potential future meta-analysis in mind.     

A meta-analysis of 25 years of mood-creativity research: Hedonic tone, activation, or regulatory focus?

This meta-analysis synthesized 102 effect sizes reflecting the relation between specific moods and creativity. Effect sizes overall revealed that positive moods produce more creativity than mood-neutral controls (r = .15), but no significant differences between negative moods and mood-neutral controls (r = -.03) or between positive and negative moods (r = .04) were observed. Creativity is enhanced most by positive mood states that are activating and associated with an approach motivation and promotion focus (e.g., happiness), rather than those that are deactivating and associated with an avoidance motivation and prevention focus (e.g., relaxed). Negative, deactivating moods with an approach motivation and a promotion focus (e.g., sadness) were not associated with creativity, but negative, activating moods with an avoidance motivation and a prevention focus (fear, anxiety) were associated with lower creativity, especially when assessed as cognitive flexibility. With a few exceptions, these results generalized across experimental and correlational designs, populations (students vs. general adult population), and facet of creativity (e.g., fluency, flexibility, originality, eureka/insight). The authors discuss theoretical implications and highlight avenues for future research on specific moods, creativity, and their relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Stroop effect: Why proportion congruent has nothing to do with congruency and everything to do with contingency.

The item-specific proportion congruent (ISPC) effect refers to the observation that the Stroop effect is larger for words that are presented mostly in congruent colors (e.g., BLUE presented 75% of the time in blue) and smaller for words that are presented mostly in a given incongruent color (e.g., YELLOW presented 75% of the time in orange). One account of the ISPC effect, the modulation hypothesis, is that participants modulate attention based on the identity of the word (i.e., participants allow the word to influence responding when it is presented mostly in its congruent color). Another account, the contingency hypothesis, is that participants use the word to predict the response that they will need to make (e.g., if the word is YELLOW, then the response is probably "orange"). Reanalyses of data from L. L. Jacoby, D. S. Lindsay, and S. Hessels (2003), along with results from new experiments, are inconsistent with the modulation hypothesis but entirely consistent with the contingency hypothesis. A response threshold mechanism that uses contingency information provides a sufficient account of the data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experimental Investigation of Clear-Water Local Scour at Pile Groups

Experiments of local scour around pile groups are carried out under steady clear-water scour conditions. A variety of conditions including different pile group arrangements, spacing, flow rates, and sediment grain sizes are considered. In total, 112 experiments are carried out. It is observed that the scour-hole depth for some cases of pile groups increases as much as two times more than its magnitude for the case of single piles. The data from this study and some laboratory experiment data from previous works are used to derive a correction factor to predict the maximum local scour depth for the pile groups. Two well-known equations, i.e., Federal Highway Administration, Hydraulic Engineering Circular No. 18, HEC-18 (reported by Richardson and Davis in 2001) and the New Zealand pier scour equation (reported by Melville and Coleman in 2000) are considered. The prediction of scour hole based on the present correction agrees well with the observations.     

(Mis-) Direction of effect sizes.

Comments on an article by Dixon et al. (see record 2007-06671-001) regarding the effect sizes they presented in their meta-analysis of psychological interventions for arthritis pain management. The author of this comment claims that some of the individual effect sizes that they presented are erroneous and have therefore undermined their cumulative effect size estimates. After examining findings from other studies, he concludes that the Dixon et al. meta-analysis reports cumulative effect sizes (Hedge’s g) that overestimate the effects of psychological treatments upon arthritis pain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A procedure for combining sample standardized mean differences and vote counts to estimate the population standardized mean difference in fixed event models.

Missing effect-size estimates pose a difficult problem in meta-analysis. Conventional procedures for dealing with this problem include discarding studies with missing estimates and imputing single values for missing estimates (e.g., 0, mean). An alternative procedure, which combines effect-size estimates and vote counts, is proposed for handling missing estimates. The combined estimator has several desirable features: (a) It uses all the information available from studies in a research synthesis, (b) it is consistent, (c) it is more efficient than other estimators, (d) it has known variance, and (e) it gives weight to all studies proportional to the Fisher information they provide. The combined procedure is the method of choice in a research synthesis when some studies do not provide enough information to compute effect-size estimates but do provide information about the direction or statistical significance of results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Isolated limb infusion with cytotoxic agents: a simple alternative to isolated limb perfusion

We use population genetics theory and computer simulations to demonstrate that population bottlenecks cause a characteristic mode-shift distortion in the distribution of allele frequencies at selectively neutral loci. Bottlenecks cause alleles at low frequency (< 0.1) to become less abundant than alleles in one or more intermediate allele frequency class (e.g., 0.1-0.2). This distortion is transient and likely to be detectable for only a few dozen generations. Consequently only recent bottlenecks are likely to be detected by tests for distortions in distributions of allele frequencies. We illustrate and evaluate a qualitative graphical method for detecting a bottleneck-induced distortion of allele frequency distributions. The simple novel method requires no information on historical population sizes or levels of genetic variation; it requires only samples of 5 to 20 polymorphic loci and approximately 30 individuals. The graphical method often differentiates between empirical datasets from bottlenecked and nonbottlenecked natural populations. Computer simulations show that the graphical method is likely (P > .80) to detect an allele frequency distortion after a bottleneck of < or = 20 breeding individuals when 8 to 10 polymorphic microsatellite loci are analyzed.