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L V Hedges

Publications and source records attributed to L V Hedges.

11 recordsLinked to original sources
PubMed1997

Are the clinical effects of homeopathy placebo effects? A meta-analysis of placebo-controlled trials.

BACKGROUND: Homeopathy seems scientifically implausible, but has widespread use. We aimed to assess whether the clinical effect reported in randomised controlled trials of homeopathic remedies is equivalent to that reported for placebo. METHODS: We sought studies from computerised bibliographies and contracts with researchers, institutions, manufacturers, individual collectors, homeopathic conference proceedings, and books. We included all languages. Double-blind and/or randomised placebo-controlled trials of clinical conditions were considered. Our review of 185 trials identified 119 that met the inclusion criteria. 89 had adequate data for meta-analysis, and two sets of trial were used to assess reproducibility. Two reviewers assessed study quality with two scales and extracted data for information on clinical condition, homeopathy type, dilution, "remedy", population, and outcomes. FINDINGS: The combined odds ratio for the 89 studies entered into the main meta-analysis was 2.45 (95% CI 2.05, 2.93) in favour of homeopathy. The odds ratio for the 26 good-quality studies was 1.66 (1.33, 2.08), and that corrected for publication bias was 1.78 (1.03, 3.10). Four studies on the effects of a single remedy on seasonal allergies had a pooled odds ratio for ocular symptoms at 4 weeks of 2.03 (1.51, 2.74). Five studies on postoperative ileus had a pooled mean effect-size-difference of -0.22 standard deviations (95% CI -0.36, -0.09) for flatus, and -0.18 SDs (-0.33, -0.03) for stool (both p < 0.05). INTERPRETATION: The results of our meta-analysis are not compatible with the hypothesis that the clinical effects of homeopathy are completely due to placebo. However, we found insufficient evidence from these studies that homeopathy is clearly efficacious for any single clinical condition. Further research on homeopathy is warranted provided it is rigorous and systematic.

Double-Blind Method↗
PubMed1995

Sex differences in mental test scores, variability, and numbers of high-scoring individuals.

Sex differences in central tendency, variability, and numbers of high scores on mental tests have been extensively studied. Research has not always seemed to yield consistent results, partly because most studies have not used representative samples of national populations. An analysis of mental test scores from six studies that used national probability samples provided evidence that although average sex differences have been generally small and stable over time, the test scores of males consistently have larger variance. Except in tests of reading comprehension, perceptual speed, and associative memory, males typically outnumber females substantially among high-scoring individuals.

Adolescent↗
PubMed1995

Meta-analysis of screening and diagnostic tests.

Screening and diagnostic tests are common in the fields of psychology, medicine, and education. Often there are several competing tests, and decisions must be made about the relative accuracy of those tests. This article describes a general measure that can be used for both continuous and dichotomous outcome measures. It is the standardized distance between the means of the 2 populations. For continuous measures, it is the effect size measure. For dichotomous measures, it is proportional to the logarithm of the odds of the sensitivity plus the logarithm of the odds of the specificity. The measure is easily computed for both kinds of outcomes. Properties of this measure are discussed, and examples are given. Ths use of this measure to compare the average performance of different tests is described.

Diagnostic Tests, Routine↗
PubMed1994

Combining graded categories: membership and typicality.

Forming a conjoint category (square tables) from constituent categories (squares and tables) has traditionally been modeled by formal set intersection. In this traditional view, in which categories are treated as precisely defined sets, an item is a member of the conjoint category if and only if it is a member of both constituent categories. However, as is now widely believed, many categories should be treated as graded, with members that vary in typicality and boundaries that are inexact. In the present article, it is argued that set intersection is inappropriate for combining graded categories. The authors propose an alternative formal mechanism in which a conjoint category is constructed from constituent categories by forming a joint distribution of values. The proposed model accounts for both membership and typicality of instances in conjoint categories, but only when the constituent categories are independent, or the relation between them is known.

Color Perception↗
PubMed1992

Memory for day of the week: a 5 + 2 day cycle.

People use a variety of schemes to keep track of time. One such scheme is the week, with its 7 distinctly named days. This article examines memory for day of the week and its relation to memory for time of day and for elapsed time (number of days). Data are presented from a study in which people answered a set of interview questions about the time of occurrence of a particular event. Two issues are addressed. The first issue concerns the way different temporal schemes are organized in relation to each other in memory. Memory for day of the week is independent of other aspects of temporal memory. The second issue concerns whether the week is organized hierarchically into either weekday periods or weekend periods or both. The weekday period forms a distinct 5-day unit within the 7-day weekly cycle. The present data, together with those from the authors' earlier work, suggest that the time an event occurred is encoded in relation to a set of separate temporal scripts (e.g., daily and weekly) and that such scripts may be hierarchically organized.

Adult↗
PubMed1991

Categories and particulars: prototype effects in estimating spatial location.

A model of category effects on reports from memory is presented. The model holds that stimuli are represented at 2 levels of detail: a fine-grain value and a category. When memory is inexact but people must report an exact value, they use estimation processes that combine the remembered stimulus value with category information. The proposed estimation processes include truncation at category boundaries and weighting with a central (prototypic) category value. These processes introduce bias in reporting even when memory is unbiased, but nevertheless may improve overall accuracy (by decreasing the variability of reports). Four experiments are presented in which people report the location of a dot in a circle. Subjects spontaneously impose horizontal and vertical boundaries that divide the circle into quadrants. They misplace dots toward a central (prototypic) location in each quadrant, as predicted by the model. The proposed model has broad implications; notably, it has the potential to explain biases of the sort described in psychophysics (contraction bias and the bias captured by Weber's law) as well as symmetries in similarity judgments, without positing distorted representations of physical scales.

Adolescent↗
PubMed1990

When is a test result abnormal? Defining limits and risks.

Test results from "normal" and "non-normal" individuals frequently overlap. Individuals with test results near the region of overlap have a high risk of being misdiagnosed. We present a statistical method for quantifying the certainty of diagnoses and defining a normal range, and illustrate its application with a specific example from a Tay-Sachs disease carrier screening program. This method can be applied to any test result based on a continuous variable and is particularly well suited to screening programs where the risk or incidence of a disease is known. We use an inconclusive range to reduce the likelihood of incorrect diagnoses resulting from measurement error and borderline results. The limits of the normal, inconclusive, and nonnormal ranges are based on three considerations: (1) the probability of misdiagnoses, (2) the expected frequency of inconclusive diagnoses, and (3) the reproducibility of the test results.

Bayes Theorem↗
PubMed1990

Reports of elapsed time: bounding and rounding processes in estimation.

The present article concerns the way temporal information is represented in memory and the processes used in estimating when events occurred. In particular, we examine the sources of bias in reports of the time that has elapsed since a target event occurred. We find that reported times are less than actual times. Evidence is presented that this forward bias is not a result of misrepresentation of elapsed time in memory, but rather reflects two factors that arise in constructing reports from inexact information in memory. One factor is subjects' imposition of an upper boundary on reports, reflecting their notion of what would constitute reasonable answers to the question asked. This boundary truncates the distribution of reports, producing forward bias. The other factor is subjects' use of rounded (prototypic) values; these values, although stated in days, actually represent larger temporal categories (e.g., 14, 21, 30, 60 days ago). The distance between rounded values increases as the temporal categories become larger. Because of decreasing precision in memory and this increase in the distance between rounded values, a broader range of values is rounded down than up, thus producing forward bias.

Humans↗
PubMed1984

Research synthesis: the state of the art.

The state of the art in research synthesis has advanced significantly in the last decade. Much of the improvement in research reviews is attributable to the application of rigorous scientific standards to the process of research synthesis. Three principal types of research syntheses are the narrative review, the replicated secondary analysis, and the meta-analysis or quantitative research synthesis. Each methodology has its strengths and weaknesses, but all have benefited from increased attention to procedural rigor. Modern methods for quantitative research synthesis have significant advantages in that they provide specific tests for the existence and consistency of relationships across studies.

Geriatrics↗
PubMedDate not supplied

Predicting metabolic control in diabetes: a pilot study using meta-analysis to estimate a linear model.

The purpose of this pilot study was to determine the feasibility of using data from replicated descriptive studies to test a four-variable model designed to explain metabolic control in diabetes. Predictors of metabolic control selected for this analysis were knowledge; health beliefs (and the subscales of barriers, commitment, cues, expectancies, impact on lifestyle, support, and susceptibility); and compliance/adherence. A total of 17 studies, published between 1982 and 1991, were located that met inclusion criteria. Findings indicated that health beliefs have direct and indirect effects on diabetes metabolic control, depending on the individual health belief subscale analyzed. For example, commitment to the benefits of therapy was found to have a statistically significant direct effect on metabolic control; barriers had a statistically significant indirect effect through compliance. The effects of knowledge were consistent throughout the five path models explored. An inverse direct effect was noted on metabolic control and a positive indirect effect was noted on metabolic control through compliance.

Attitude to Health↗