Meta-analysis Of Experiments Research Articles

Meta-analysis of experimental warming on soil invertase and urease activities

ABSTRACTSoil enzymes are regulate terrestrial carbon (C) and nitrogen (N) cycles, and how the activity of these enzymes are affected by soil warming duration is unclear. In the study, the effect of experimental soil warming duration (<2 years and >2 years) on invertase and urease activities were examined by meta-analysis. Soil warming increased invertase activity by 22% (<2 years) and 16% (>2 years), respectively, while they increased urease by 29% and 9%. Meta-analysis of soil warming experiments found that warming by less than 1.5°C increased invertase by 22%, while warming it by more than 1.5°C increased invertase by 29%; the corresponding increases in urease were 16% and 8%. These effects of experiment warming differed among ecosystem types, with warming-induced increases being greatest in forest ecosystem. The results of this meta-analysis suggest that invertase and urease become less responsive to warming over longer periods and invertase with greater warming-responsiveness than urease activity.

How Responsive are Political Elites? A Meta-Analysis of Experiments on Public Officials

AbstractIn the past decade, the body of research using experimental approaches to investigate the responsiveness of elected officials has grown exponentially. Given this explosion of work, a systematic assessment of these studies is needed not only to take stock of what we have learned so far about democratic responsiveness, but also to inform the design of future studies. In this article, I conduct the first meta-analysis of all experiments that examine elite responsiveness to constituent communication. I find that racial/ethnic minorities and messages sent to elected officials (as opposed to non-elected) are significantly less likely to receive a response. A qualitative review of the literature further suggests that some of these inequalities in responsiveness are driven by personal biases of public officials, rather than strategic, electoral considerations. The findings of this study provide important qualifications and context to prominent individual studies in the field.

Negative, neutral, and positive interactions among nonnative plants: patterns, processes, and management implications.

The movement of species is one of the most pervasive forms of global change, and few ecosystems remain uninvaded by nonnative species. Studying species interactions is crucial for understanding their distribution and abundance, particularly for nonnative species because interactions may influence the probability of invasion and consequent ecological impact. Interactions among nonnatives are relatively understudied, though the likelihood of nonnative species co-occurrence is high. We quantify and describe the types of interactions among nonnative plants and determine what factors affect interaction outcomes for ecosystems globally. We reviewed 65 studies comprising 201 observations and recorded the interaction type, traits of the interacting species, and study characteristics. We conducted a census of interaction types and a meta-analysis of experiments that tested nonnative competition intensity. Both methods showed that negative and neutral interactions prevailed, and a number of studies reported that the removal of a dominant nonnative led to competitive release of other nonnatives. Positive interactions were less frequently reported and positive mean effect sizes were rare, but the plant characteristics nitrogen fixation, life cycle (annual or perennial), and functional group significantly influenced positive interactions. Positive interactions were three times more frequent when a neighboring nonnative was a nitrogen fixer and 3.5 times lower when a neighboring nonnative was an annual. Woody plants were two or four times more likely to have positive interactions relative to grasses or herbs, respectively. The prevalence of negative interactions suggests that managers should prepare for reinvasion of sites when treating dominant nonnatives. Though positive interactions were infrequent, managers may be able to anticipate positive interactions among nonnatives based upon traits of the co-occurring invaders. Predicting positive nonnative interactions is an important tool for determining habitat susceptibility to a particular invasion and for prioritizing management of nonnatives with a higher likelihood of positive interactions.

A meta-analysis of multiple matched copy number and transcriptomics data sets for inferring gene regulatory relationships.

Inferring gene regulatory relationships from observational data is challenging. Manipulation and intervention is often required to unravel causal relationships unambiguously. However, gene copy number changes, as they frequently occur in cancer cells, might be considered natural manipulation experiments on gene expression. An increasing number of data sets on matched array comparative genomic hybridisation and transcriptomics experiments from a variety of cancer pathologies are becoming publicly available. Here we explore the potential of a meta-analysis of thirty such data sets. The aim of our analysis was to assess the potential of in silico inference of trans-acting gene regulatory relationships from this type of data. We found sufficient correlation signal in the data to infer gene regulatory relationships, with interesting similarities between data sets. A number of genes had highly correlated copy number and expression changes in many of the data sets and we present predicted potential trans-acted regulatory relationships for each of these genes. The study also investigates to what extent heterogeneity between cell types and between pathologies determines the number of statistically significant predictions available from a meta-analysis of experiments.

Where Am I? A Meta-Analysis of Experiments on the Effects of Progress Indicators for Web Surveys

The use of progress indicators seems to be standard in many online surveys. Researchers include them in surveys in the hope they will help reduce drop-off rates. However, there is no consensus in the literature regarding their effects. In this meta-analysis, we analyzed 32 randomized experiments comparing drop-off rates of an experimental group who completed an online survey in which a progress indicator was shown to drop-off rates of a control group to whom the progress indicator was not shown. In all the studies, a drop-off was defined as a discontinuance of the survey (at any point) after it has begun, resulting in failure to complete the survey. Three types of progress indicators were analyzed: constant, fast-to-slow, and slow-to-fast. Our results show that, overall, using a constant progress indicator does not significantly help reduce drop-offs and that effectiveness of the progress indicator varies depending on the speed of indicator: Fast-to-slow indicators reduced drop-offs, whereas slow-to-fast indicators increased drop-offs. We also found that among the studies in which a small incentive was promised, showing a constant progress indicator increased the drop-off rate. These findings question the common belief that progress indicators help reduce drop-off rates.

United we stand, divided we fall: a meta-analysis of experiments on clonal integration and its relationship to invasiveness

Many ecosystems are dominated by clonal plants. Among the most distinctive characteristics of clonal plants is their potential for clonal integration (i.e. the translocation of resources between interconnected ramets), suggesting that integration may play a role in their success. However, a general synthesis of effects of clonal integration on plant performance is lacking. We conducted a meta-analysis on the effects of clonal integration on biomass production and asexual reproduction of the whole clone, the recipient part (i.e. the part of a clone that imports resources) and the donor part (i.e. the part of a clone that exports resources). The final dataset contained 389 effect sizes from 84 studies covering 57 taxa. Overall, clonal integration increased performance of recipient parts without decreasing that of donor parts, and thus increased performance of whole clones. Among the studies and taxa considered, the benefits of clonal integration did not differ between two types of experimental approaches, between stoloniferous and rhizomatous growth forms, between directions of resource translocation (from younger to older ramet or vice versa), or among types of translocated resources (water, nutrients and carbohydrates). Clonal taxa with larger benefits of integration on whole-clone performance were not more invasive globally, but taxa in which recipient parts in unfavorable patches benefited more from integration were. Our results demonstrate general performance benefits of clonal integration, at least in the short term, and suggest that clonal integration contributes to the success of clonal plants.

Crossing Disciplinary Boundaries: Going Beyond Even Meta-Analysis of Distant Intention

In his excellent article, ‘‘Can We Just Help by Good Intentions? A Meta-Analysis of Experiments on Distant Intention Effects,’’ Stefan Schmidt, PhD, demonstrates persuasively that there are an abundance of studies indicating the positive effect of benevolent intention. His meta-analysis of 11 studies, with 576 single sessions, on studies involving the question of whether the attentional performance of a participant can be varied by the support of a remote person, shows a reasonably consistent, although small, effect size. Interestingly, there were cultural Western (United States and United Kingdom) and Eastern (Indonesia) differences in operator performance. Schmidt notes that these attention-focusing facilitation experiments (AFFEs) are part of a larger series of distant intentionality experiments, sometimes known as direct mental interaction in living systems (DMILS). Two other types of DMILS occur in the experimental setup whereby a participant attempts to change the electrodermal activity (EDA) of a subject from a distance (EDA-DMILS). The second type of DMILS is remote staring, whereby the dependent variable is the EDA physiologic arousal of the person being stared at. Importantly, subsequent to his meta-analysis of the AFFE experiments, Schmidt presents two previously performed meta-analyses on DMILS and remote staring that produced almost the same small, but significant effect size. Based on this, he noted that, whether the dependent variable in an experiment was physiologic or behavioral seems to be of little importance. Nor was the effect size related to the specific task. Schmidt suggests the possibility that, because it is not the specificity of task (i.e., helping, activating, or staring) that is important, we might be left with only the intentional component toward the remote person. This, he speculates, might be related to a number of areas in which distant intention seems to be at work, including healing and meditation. This is wonderful stuff, indeed. At the same time that we can acknowledge and appreciate the quality of Schmidt’s meticulous analysis, and the creative comparison of his meta-analysis to previous metaanalyses, we might also stop to consider and compare applications of intention beyond those directed at remote persons. He is exactly ‘‘on the money’’ in trying to go beyond his present meta-analysis to seek other comparisons. Perhaps the exercise needs to be extended beyond the

Can We Help Just by Good Intentions? A Meta-Analysis of Experiments on Distant Intention Effects

In recent years, several clinical trials have assessed effects of distant healing. The basic question raised by these studies is whether a positive distant intention can be related to some outcome in a target person. There is a specific simple experimental setup that tests such a basic assumption. The task is to focus attention and to indicate unwanted mind wandering by a button press while at the same time a second remote person is either supporting this performance or not according to a randomized schedule. A meta-analysis was conducted to assess the overall effect of this experimental approach. A systematic literature search yielded 11 eligible studies, with 576 single sessions and almost identical design, that were conducted on three different continents. Study parameters were extracted and combined with a random-effects model. The model yielded an overall effect size of d=0.11 (p=0.03). Furthermore, there was a significant difference of the frequency of button presses between studies conducted in Indonesia and the Western hemisphere (p<0.001). Two (2) similar experimental setups applying electrodermal activity as dependent variable meta-analyzed earlier showed almost identical effect sizes. This can be considered as mutual validation of the three data sets. The hypothesis of the positive effect of benevolent intentions is supported by the data presented. It is concluded that especially the intentional aspect common to all three different tasks may be responsible for these unorthodox findings. These finding may have implications for distant healing research and health care as well as for meditation performance.

Looking for answers to questions about heat stress: researchers are getting warmer

While the public continues to debate the reality of global warming, scientists should prepare to deal with the consequences of this very real phenomenon. Our planet has warmed by 0·13 ° C per decade since 1956, and will likely warm more rapidly in the decades to come (Intergovernmental Panel on Climate Change 2007). This global measure of thermal change belies the more pronounced and less predictable changes that are occurring on smaller scales (Walther et al . 2002). For example, the greater frequency and intensity of heat waves in many areas ranks among the more threatening aspects of anthropogenic climate change. Will acclimation or adaptation enable the persistence of populations that face such thermal stresses? And, if populations do persist, will their densities and compositions change radically? To answer these questions, we must understand a suite of phenomena, ranging from the mechanistic basis of thermotolerance to the demographic and ecological consequences of thermal plasticity (Angilletta 2009). This issue of Functional Ecology contains four papers that improve our understanding of these phenomena. To enhance your appreciation of this collection, I briefly highlight the significance of each paper while laying out the broader issues concerning the biological impacts of heat stress. During rapid warming, the performance of an organism depends on its capacity to protect and modify its cellular structures. Brief exposure to extreme heat often causes greater thermotolerance within hours, a phenomenon referred to as

Predation on mutualists can reduce the strength of trophic cascades

Ecologists have put forth several mechanisms to predict the strength of predator effects on producers (a trophic cascade). We suggest a novel mechanism--in systems in which mutualists of plants are present and important, predators can have indirect negative effects on producers through their consumption of mutualists. The strength of predator effects on producers will depend on their relative consumption of mutualists and antagonists, and on the relative importance of each to producer population dynamics. In a meta-analysis of experiments that examine the effects of predator reduction on the pollination and reproductive success of plants, we found that the indirect negative effects of predators on plants are quite strong. Most predator removal experiments measure the strength of predator effects on producers through the antagonist pathway; we suggest that a more complete understanding of the role of predators will be achieved by simultaneously considering the effects of predators on plant mutualists.

Light regime and consumer control of autotrophic biomass

Summary 1 Autotrophic biomass is often regulated by resource supply and consumer presence. Most studies on top-down vs. bottom-up control of plant biomass focus on nutrients as basal resources, whereas light has received considerably less attention. 2 Effects of light and nutrients may differ because light represents a vertical resource and plant adaptations to acquire light might counteract or facilitate consumer effects. I tested the interaction between light supply and consumer presence in a meta-analysis of experiments that manipulated both these factors factorially and measured the biomass of benthic algae (periphyton). 3 Both grazer removal and light enhancement had positive effects on algal biomass. These two factors showed strong interactions, which exceeded previously observed interaction terms between nutrient supply and grazer removal. Positive light effects on algal biomass were primarily observed in the absence of grazers. Grazer effects became stronger at high light supply, which indicated that high light favours algal growth types that are easily ingested. 4 Further analyses showed that light effects increased with trophic state of the habitat and with algal biomass, indicating enhanced importance of light limitation and self-shading at high nutrient supply. Grazer effects depended on grazer biomass and varied with type of experimental manipulation. 5 This study implies that light is of similar importance as nutrients in resource control of benthic algal biomass. High light levels simultaneously enhance consumer control of algal biomass, resulting in strong resource vs. consumer interactions. Light competition and consumer presence pose a trade-off on algal growth, where growth form may distinguish between adaptations to acquire light and to avoid consumption.

Meta-analysis of experiments investigating cadmium accumulation in the liver and kidney of sheep

Cadmium (Cd) accumulates in the human food chain and poses a risk of kidney dysfunction (Fanconi Syndrome) and bone disorders in humans. The margin of safety between typical Cd intakes by humans and levels associated with toxicity is smaller than for other metals. Consumption of just one sheep kidney could cause an average adult person to exceed their Provisional Maximum Tolerable Daily Intake. However, the rate of accumulation in sheep’s liver and kidney, the primary target organs for Cd accumulation, is unclear. This makes prediction of the effects of varying Cd intake by sheep on the Cd concentration in these organs difficult. We undertook a meta-analysis of independent feeding trials, which sought to integrate previous findings in order to review existing legislation on permitted levels of Cd in animal feeds and organs. Resulting predictions on Cd accumulation in sheep liver and kidneys are applicable to the broad set of exposure situations investigated in the individual studies.

Detecting Publication Bias in Meta-analyses: A Case Study of Fluctuating Asymmetry and Sexual Selection.

Those familiar with human nature and the publication process acknowledge that biases due to selective reporting of results are likely widespread in all fields of academic inquiry that depend on tools of statistical inference (e.g., see Begg and Berlin 1988; Iyengar and Greenhouse 1988; and the extensive discussion following each). However, although qualitative and quantitative methods exist for assessing the prevalence of selective reporting, and selective reporting has been studied in the medical and social sciences (Begg 1994, and references therein), the issue has received little attention in recent meta-analyses of ecological and evolutionary patterns. Clearly, “if publication bias is present, and if it operates in the same direction for all studies (as is likely), then [meta-analysis] is likely not only to produce biased summary estimates but also to produce estimates which are apparently precise and accurate leading to conclusions which may not only be wrong but appear convincing” (Begg and Berlin 1988, p. 437). To biologists unacquainted with the formal study of publication patterns, the terms “selective reporting” (statistical significance of an outcome influences its likelihood of being reported or published) and “publication bias” (the inflation of average effect size due to selective reporting) may imply a conscious intent to deceive, but this

Guest editorial: Improving the interpretation and reporting of quantitative research

Guest editorial: Improving the interpretation and reporting of quantitative research

Meta-analyses of dietary fats and mammary neoplasms in rodent experiments.

We review two meta-analyses of experiments on dietary fat and mammary tumor incidence in rodents, emphasizing a recent meta-analysis on the effects of different types of dietary fatty acids. This analysis shows that n-6 polyunsaturated fatty acids most strongly enhance mammary tumors in rodents, and saturated fats also enhance these tumors but less strongly. Further, the analysis shows that energy restriction protects against mammary tumors. We show that these results agree qualitatively with estimates of effects on human breast cancer derived from international correlations.

Meta-analysis of experiments with matched groups or repeated measures designs.

Tests for experiments with matched groups or repeated measures designs use error terms that involve the correlation between the measures as well as the variance of the data. The larger the correlation between the measures, the smaller the error and the larger the test statistic. If an effect size is computed from the test statistic without taking the correlation between the measures into account, effect size will be overestimated . Procedures for computing effect size appropriately from matched groups or repeated measures designs are discussed. The purpose of this article is to address issues that arise when meta-analyses are conducted on experiments with matched groups or repeated measures designs. It should be made clear at the outset that although this article pertains to metaanalyses of experiments with correlated measures, it does not pertain to meta-analyses of correlations. Such experimental designs, often called matched groups designs or designs with repeated measures, we call correlated designs (CDs), and their analysis is decidedly different from that of the independent groups designs (IGDs). The matched groups design in its simplest form occurs when subjects are matched on some variable and then randomly assigned by matched pairs to experimental and control conditions. The correlation for this type of CD is the correlation between experimental and control scores across matched pairs. The second type of CD is the repeated measures design, which in its simplest form tests the same subject under both experimental and control conditions, usually in random or counterbalanced orders to minimize carryover. The correlation of importance here is the correlation that commonly occurs between the repeated measures, and this correlation is often quite high in human research.

Meta-analysis of experiments with matched groups or repeated measures designs.

Meta-analysis of experiments with matched groups or repeated measures designs.