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Results for “Effect Modifier, Epidemiologic”

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PubMed1998

Combining studies using effect sizes and quality scores: application to bone loss in postmenopausal women.

This article presents a random effects model that uses effect sizes (ES) and quality scores to integrate results from investigations. An empirical example is given with data obtained from a meta-analysis on the effectiveness of physical activity in the prevention of bone loss in healthy postmenopausal women. A Medline search was performed to locate relevant studies published in French or English between January 1966 and May 1996. Three independent reviewers extracted data from studies. Effect sizes were calculated according to the method of Hedges and Olkin. A modified version of Chalmers' scale was utilized to calculate quality scores. DerSimonian and Laird's method with incorporation of the quality scores was used to estimate the overall effect size. Quality scores and the inverse of the variances were included as weights when combining studies. The overall estimate and standard error (SE) of the effect of physical activity on spinal bone mineral density loss in healthy postmenopausal women was ESoverall = 0.4263 (1.1361). When compared to other meta-analysis methods such as the fixed effects model and the model of DerSimonian and Laird without the quality score (DL), the new model generated comparable estimators (fixed effects model's ESoverall (SE) = 1.2724 (0.0139), DLs ESoverall (SE) = 0.3958 (1.2370)). Due to the heterogeneity that existed between studies, a random effects model was more appropriate then a fixed effects model. However, it resulted in wider confidence intervals, as expected. It was shown empirically that the model using quality scores generated narrower confidence intervals than the model of DL alone. The inclusion of covariates such as quality scores in meta-analyses permits the quantification of the variation between studies.

Analysis of Variance↗

PubMed1999

Stratified randomization for clinical trials.

Trialists argue about the usefulness of stratified randomization. For investigators designing trials and readers who use them, the argument has created uncertainty regarding the importance of stratification. In this paper, we review stratified randomization to summarize its purpose, indications, accomplishments, and alternatives. In order to identify research papers, we performed a Medline search for 1966-1997. The search yielded 33 articles that included original research on stratification or included stratification as the major focus. Additional resources included textbooks. Stratified randomization prevents imbalance between treatment groups for known factors that influence prognosis or treatment responsiveness. As a result, stratification may prevent type I error and improve power for small trials (<400 patients), but only when the stratification factors have a large effect on prognosis. Stratification has an important effect on sample size for active control equivalence trials, but not for superiority trials. Theoretical benefits include facilitation of subgroup analysis and interim analysis. The maximum desirable number of strata is unknown, but experts argue for keeping it small. Stratified randomization is important only for small trials in which treatment outcome may be affected by known clinical factors that have a large effect on prognosis, large trials when interim analyses are planned with small numbers of patients, and trials designed to show the equivalence of two therapies. Once the decision to stratify is made, investigators need to chose factors carefully and account for them in the analysis.

Bias↗

PubMed2000

Misleading funnel plot for detection of bias in meta-analysis.

Publication and other forms of selection biases pose a threat to the validity of meta-analysis. Funnel plots are usually used to detect such biases; asymmetrical plots are interpreted to suggest that biases are present. Using 198 published meta-analyses, we demonstrate that the shape of a funnel plot is largely determined by the arbitrary choice of the method to construct the plot. When a different definition of precision and/or effect measure were used, the conclusion about the shape of the plot was altered in 37 (86%) of the 43 meta-analyses with an asymmetrical plot suggesting selection bias. In the absence of a consensus on how the plot should be constructed, asymmetrical funnel plots should be interpreted cautiously. These findings also suggest that the discrepancies between large trials and corresponding meta-analyses and heterogeneity in meta-analyses may also be determined by how they are evaluated.

Data Interpretation, Statistical↗

PubMed2001

Smoking, other risk factors and fibrinogen levels. evidence of effect modification.

PURPOSE: Recent investigations have indicated that smoking may act as an important modifier of the risk associated with dyslipidemia. We hypothesized as a potential mechanism that smoking modifies the association between traditional risk factors of early atherosclerosis, such as dyslipidemia, hypertension, or diabetes, with fibrinogen, a risk factor more closely related to plaque progression and thrombosis. METHODS: The sample for this cross-sectional study, was collected from the MONICA Augsburg population survey of 1989/90 and included 1840 men and 1784 women, aged 25 to 64 years. Traditional risk factors hypertension, diabetes mellitus, and dyslipidemia were assessed by personal interviews, and medical examinations. Plasma fibrinogen concentration was determined by nephelometry. Effect modification was assessed by stratified analyses and tests for statistical interaction. RESULTS: Fibrinogen levels were higher in women than in men and, after adjustment for potential confounders, higher in smokers than in nonsmokers (each p < 0.001). The effect of smoking was greater in men (p < 0.001). The elevation of mean adjusted fibrinogen levels associated with hypertension or with diabetes in men was significantly higher in smokers as compared to nonsmokers (test for interaction, p < 0.001). By contrast, smoking in women showed significantly stronger impacts only with regard to the association of dyslipidemia and fibrinogen (p < 0.001). Comparing groups of subjects with increasing numbers of concomitant risk factors, stratified according to their smoking status, effect modification by smoking was particularly evident in male participants with two or more risk factors. Numbers of women with more than one risk factor and smoking were too low for analysis. CONCLUSIONS: We demonstrate that smoking contributes more than additively to the strong influences of single and combined traditional risk factors on fibrinogen levels. These data confirm that smoking is a dominant determinant of fibrinogen levels in the general population.

Adult↗

PubMed1997

Employment status and high blood pressure in women: variations by time and by sociodemographic characteristics.

PURPOSE: The association between employment status and high blood pressure in women was examined at two time periods to determine if associations between employment status and high blood pressure varied by time period or by age, race, education, marital status, or parental status. METHODS: Women participants from the National Health Examination Survey (1960) and the Second National Health and Nutrition Survey (1976-1980) between the ages of 25 and 64 and currently employed or keeping house were included. Logistic regression analysis was used to examine the cross-sectional association between employment status and high blood pressure in each survey, taking into account potential effect modifiers and covariates. RESULTS: In 1960 employment was associated with a slight, but not statistically significant, elevation in odds of high blood pressure. In 1976-1980, it was associated with a modest but significant reduction in odds of high blood pressure. Variations in associations occurred by marital status (protective associations were limited to unmarried women) and race (associations were of stronger magnitude among African-American women). CONCLUSIONS: The employment status-high blood pressure relationship shifted across surveys. Changes in the composition of the employed and nonemployed groups account for at least part of the varying relationships.

Adult↗

PubMed1999

Work and leisure time physical activity and mortality in men and women from a general population sample.

PURPOSE: The purpose of this study was to examine the long-term relationships between total physical activity and mortality from all causes and coronary heart disease (CHD) in the general population. METHODS: A prospective design was used, following participants for 29 years, beginning in 1960. The study population consisted of a randomly selected sample of white male (n = 698) and female (n = 763) residents of Buffalo, New York with a 79.0% participation rate and follow-up rates of 96.0% and 90.2% in males and females, respectively. At baseline, comprehensive information was obtained regarding participants' usual physical activity at work and during leisure time. RESULTS: As of December 31, 1989, three hundred and two (43.3%) men and 276 (41.0%) women died, 109 (15.6%) and 81 (10.6%) from CHD, respectively. In men, a significant interaction was found between activity and body mass index (BMI) for both outcomes. In women, a significant activity by age interaction was observed. In non-obese men (BMI<27.02), activity was inversely associated with all-cause [relative risk (RR) = 0.59; 95% confidence interval (CI), 0.39-0.89] and CHD mortality (RR = 0.39; 95% CI, 0.18-0.83), independent from the effects of age and education. No such associations were found in obese men and increased risks could not be ruled out. Among women, younger participants (age <60 years) had a significantly reduced risk of CHD death with increased activity (RR = 0.26; 95% CI, 0.07-0.99). No other significant associations were observed. CONCLUSIONS: Physical activity favorably influences mortality risks in non-obese men and younger women. Gender-specific factors should be considered for potential effect modification.

Adolescent↗

PubMed2000

Using a new method of gathering patient satisfaction data to assess the effects of organizational factors on primary care quality.

BACKGROUND: As health care in the United States evolves increasingly toward managed care, there are continuing concerns about maintaining the quality of the physician-patient interaction, of which patient satisfaction is one measure. A quality assessment tool that measures both patient satisfaction with care and the ways organizational factors affect satisfaction will enable clinicians and administrators to redesign the care process accordingly. SURVEY METHODOLOGY: The measure of the quality of a physician office visit includes both the administration of a standardized satisfaction instrument and direct observation of the patient throughout the care process. This methodology was tested in 1997-1998 on an initial sample of 291 patients at a large multispecialty medical group in northern California. The surveyor recorded objective characteristics of the visit, surveyed patients about their impression of certain aspects of the visit related to satisfaction, and administered a standardized visit satisfaction survey. A second set of control patients who visited the same physician on the same day was contacted by phone and given the satisfaction survey two to four weeks later. PRINCIPAL FINDINGS: Patients readily accepted the presence of a surveyor during their visit, with an overall response rate of 78%. While patients contacted retrospectively gave lower satisfaction ratings, the presence of a surveyor did not affect patients' satisfaction responses. Data obtained by using the concurrent methodology provides significant information about organizational factors influencing patient satisfaction. CONCLUSIONS: Measuring patient satisfaction concurrently during a physician office visit offers an attractive alternative to other methods of measuring this key aspect of quality.

California↗

PubMed2001

Derogation of student female athletes who consult a sport psychologist: an alternative perspective on the negative halo effect.

This study attempts to further research female student athletes' perceptions of the sport psychologist and other sport and mental health professionals. 90 British student athletes from 17 different sports completed a two-part questionnaire to examine the potential derogation effect as a result of consulting one of three identified professionals and to explore the perceived definition and role of the sport psychologist. A fictitious selection report of a female field hockey player was presented to subjects with coach, sport psychologist and psychotherapist as the three professionals. It was hypothesised that subjects' recommendations regarding selection would differ depending on the consultant used. No differences were found which suggests the absence of a negative halo effect and that derogation would not occur within this sample group. Definitions and perceived role of the sport psychologist varied with the subjective tone of the responses from participants being mainly positive (74%). These results indicate that this female student athlete sample has a moderated, even a positive, perception of the sport psychologist. A general acceptance of the sport psychologist falls in line with the suggestions of Murstein and Fontaine (1993) concerning a reported increase in acceptance of mental health professionals.

Adult↗

PubMed2000

Impact of quality items on study outcome. Treatments in acute lateral ankle sprains.

OBJECTIVE: This study investigates the influence of different aspects of methodologic quality on the conclusions of a systematic review concerning treatments of acute lateral ankle sprain. METHOD: A data set of a systematic review of 44 trials was used, of which 22 trials could be included in this study. Quality assessment of the individual studies was performed using the Delphi list. We calculated effect sizes of the main outcome measure in each study in order to evaluate the relationship between overall quality scores and outcome. Next, we investigated the impact of design attributes on pooled effect sizes by subgroup analysis. RESULTS: The quality of most studies (82%) was low; only 4 of 22 trials were of high quality. Studies with proper randomization and blinding procedure produce a slightly higher (not statistically significant) effect estimate compared to the other studies. CONCLUSION: Previous research has suggested that methodologically poorly designed studies tend to over-estimate the effect estimate. Our study does not confirm these conclusions.

Ankle Injuries↗

PubMed1992

Memory improvements and pharmacological treatment: a method to distinguish direct effects on memory from secondary effects due to attention improvement.

Chronic cerebrovascular disturbances of the aged are characterized by a decline of attention. When these patients undergo pharmacological treatment, it is very difficult to distinguish between a direct benefit and/or a secondary effect on memory resulting from attention improvement. In our study we have proposed and evaluated a new method for identifying the different components of therapeutic efficacy on memory and attention in chronic cerebrovascular patients. This method is based on the use of the Randt Memory Test, traditional scores of memory efficiency (Acquisition, Recall, and a combined index), and the RMT three-factor scores derived from a structural model of memory functioning. The three scores have been called Encoding and Organization, Cognitive Efficiency, and Attention Efficiency. Participants were 96 selected chronic cerebrovascular patients treated in a double-blind study for 12 weeks with dihydroergocristine versus placebo. While changes in both acquisition and recall scores were related to the treatment, only changes of the Encoding and Organization factor scores were systematically related to therapy. Changes in Attention Efficiency were positively related to therapy only in proportion to the degree of cerebrovascular impairment.

Attention↗

PubMedDate not supplied

Using interactive videodisc to test advanced airway management skills.

PURPOSE: To evaluate the effectiveness of the Actronics Interactive Learning System to teach the psychomotor skills of advanced airway management compared to the traditional method of lecture/demonstration. METHODS: The study was a nonrandomized, nonequivalent comparison group design of a convenience sample of 86 American Heart Association (AHA), advanced cardiac life support (ACLS) students, who obtained instruction in airway management by the interactive videodisc (IVD) learning system (n = 41), or by the traditional method of demonstration/return demonstration (n = 45). The evaluation criteria for the students were based on the number of attempts required to perform successfully endotracheal (ET) intubation and esophageal obturator airway (EOA) insertion. RESULTS: No statistically significant differences in the performance of ET insertion between the IVD and the traditional method of instruction could be demonstrated. However, initial certifiers for ACLS learning EOA insertion by the IVD method had a treatment effect (p = 0.004) compared to ACLS students learning by the traditional method. This treatment effect was not noted with ET intubation and EOA insertion for students seeking recertification. In a post-test satisfaction questionnaire, 34 IVD students reported satisfaction with learning airway management using this instructional method, but also expressed a preference to have an ACLS instructor available. CONCLUSION: This study highlights the role of IVD in teaching the complex skills of advanced airway management.

Adult↗

PubMed2003

Neuropsychological effects of treatments for adults with cancer: a meta-analysis and review of the literature.

A meta-analysis was conducted to evaluate possible neuropsychological effects of treatments for cancer in adults. A search revealed 30 studies, encompassing 29 eligible samples, and leading to inclusion of a total of 838 patients and control participants. A total of 173 effect sizes (Cohen's d) were extracted across 7 cognitive domains and as assessed in the literature via 3 methods of comparison (post-treatment compared with normative data, controls, or baseline performance). Statistically significant negative effect sizes were found consistently across both normative and control methods of comparison for executive function, verbal memory, and motor function. The largest effects were for executive function and verbal memory normative comparisons (-.93 and -.91, respectively). When limiting the sample of studies in the analyses to only those with relatively "less severe" diagnoses and treatments, the effects remained. While these results point toward some specific cognitive effects of systemic cancer therapies in general, no clear clinical implications can yet be drawn from these results. More research is needed to clarify which treatments may produce cognitive decrements, the size of those effects, and their duration, while ruling out a wide variety of possible mediating or moderating variables.

Adult↗

PubMed1998

On the generalizability of statistical expressions of health related quality of life instrument responsiveness: a data synthesis.

Responsiveness statistics have been suggested as criteria for selecting health-related quality of life (HRQoL) instruments or for calculating the required sample size. This paper raises questions about the stability of estimates of instrument responsiveness. The questions are examined by use of data synthesis. A literature search identified instances where two HRQoL instruments were used concurrently on two or more occasions. An effect size difference between the instruments was calculated. The distribution of the differences in the effect size between pairs of instruments used conjointly in different applications was used as an indicator of variation in responsiveness. The effect size for all possible published uses of generic and disease-specific HRQoL instruments was also examined. Responsiveness was found to be subject to considerable variation. Disease-specific instruments were found to be consistently more responsive than generic instruments. The authors suggest use of responsiveness data should be restricted to expanding pilot study results.

Analysis of Variance↗

PubMed2001

Assessment of exposure to political violence and other potentially traumatizing events. A critical review.

This paper focuses on the common use of internal-consistency reliability, test-retest, and interrater correlations based on counts of events, events sampling, and factor-analytic techniques in assessment of exposure to political violence and other potentially traumatizing events. The author attributes the continued use of these strategies to a tendency among researchers to identify items from conventional events lists as effect indicators. Through a discussion of four alternative measurement models, the rationale is provided for the proposition that exposure to political violence and similar constructs should be treated as composite variables with causal indicators, rather than as latent variables with effect indicators.

Bias↗

PubMed2001

Eyewitness accuracy rates in sequential and simultaneous lineup presentations: a meta-analytic comparison.

Most police lineups use a simultaneous presentation technique in which eyewitnesses view all lineup members at the same time. Lindsay and Wells (R. C. L. Lindsay & G. L. Wells, 1985) devised an alternative procedure, the sequential lineup, in which witnesses view one lineup member at a time and decide whether or not that person is the perpetrator prior to viewing the next lineup member. The present work uses the technique of meta-analysis to compare the accuracy rates of these presentation styles. Twenty-three papers were located (9 published and 14 unpublished), providing 30 tests of the hypothesis and including 4,145 participants. Results showed that identification of perpetrators from target-present lineups occurs at a higher rate from simultaneous than from sequential lineups. However, this difference largely disappears when moderator variables approximating real world conditions are considered. Also, correct rejection rates were significantly higher for sequential than simultaneous lineups and this difference is maintained or increased by greater approximation to real world conditions. Implications of these findings are discussed.

Bias↗

PubMed2001

Mortality and temperature in Oslo, Norway, 1990-1995.

The associations between temperature and daily mortality was studied among the citizens of Oslo, Norway, 1990-1995. Data on daily mortality were linked with daily temperatures, relative humidity, wind velocity and air pollution. At temperatures below 10 degrees C, a 1 degrees C fall in the last 7 days average temperature increased the daily mortality from all diseases by 1.4%, respiratory diseases 2.1%, and cardiovascular diseases 1.7%. Above 10 degrees C, there was no statistically significant increase in daily mortality, except for respiratory mortality, which increased by 4.7% per 1 degrees C increase in the last 7 days average temperature. Daily mortality in Oslo increases with temperatures falling below 10 degrees C. The increase starts at lower temperatures than shown in warmer regions of the world, but at higher temperatures than in regions with even colder climates. As well insulated and heated dwellings are standard in Norway today, more adequate clothing during outdoor visits is probably the most important preventive measure for temperature related mortality.

Air Pollutants↗

PubMed2002

Smooth conditional distribution function and quantiles under random censorship.

We consider a nonparametric random design regression model in which the response variable is possibly right censored. The aim of this paper is to estimate the conditional distribution function and the conditional alpha-quantile of the response variable. We restrict attention to the case where the response variable as well as the explanatory variable are unidimensional and continuous. We propose and discuss two classes of estimators which are smooth with respect to the response variable as well as to the covariate. Some simulations demonstrate that the new methods have better mean square error performances than the generalized Kaplan-Meier estimator introduced by Beran (1981) and considered in the literature by Dabrowska (1989, 1992) and Gonzalez-Manteiga and Cadarso-Suarez (1994).

Effect Modifier, Epidemiologic↗

PubMed1997

Trends in urinary bladder cancer incidence in Sweden 1960-93 with special reference to histopathology, time period, birth cohort, and smoking.

This study investigates the incidence trends of urinary bladder cancer in Sweden from 1960 through 1993 (a total of 46,211 cases). Age-standardized incidence rates increased among men from 14.6 per 10(5) in 1960 to 33.5 in 1993 and among women from 4.8 to 8.8, corresponding to an average annual increase of 2.4 percent (95 percent confidence interval [CI]) = 2.0-2.7 percent) and 1.1 percent (CI = 0.9-1.4 percent), respectively. The largest increase occurred in the oldest age-groups. The proportion of patients with transitional cell carcinoma increased in men from 66.0 percent in 1960-64 to 93.6 percent in 1990-93 and in women from 61.0 percent to 89.4 percent. The proportion of patients with papillomas decreased, whereas those with adenocarcinoma and squamous cell carcinoma were stable. Regression modeling (based on the period 1960-89) showed a strong linear effect due to either period and/or cohort. Among men, additional non-linear effects by both period and cohort were obtained. The cohort effects were more important. Cohort data on having smoked daily showed considerable similarities with the estimated cohort-effects. Our findings suggest that the increase of tobacco smoking in successive generations can explain the increase in incidence rates of bladder cancer in Sweden, whereas improved diagnostic activities and registration are less likely to explain fully the changes in incidence rates.

Adult↗