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PubMed2003

The effect of clustering of outcomes on the association of procedure volume and surgical outcomes.

BACKGROUND: A large body of literature documents associations between the volume of cases a hospital or surgeon treats and clinical outcomes. Most of these studies have used conventional statistical methods that do not recognize the fact that hospitals or surgeons with similar volumes may have very different outcomes because of systematic differences in processes of care, a phenomenon that exaggerates the true statistical significance of the effect of volume on outcome. OBJECTIVE: To describe methods to assess the degree of this "clustering" of outcomes and to explore the impact of available statistical techniques that correct for clustering. DESIGN: Reanalysis of 3 previously published volume-outcome studies. SETTING: Medicare beneficiaries 65 years of age or older undergoing surgery for colon, prostate, or rectal cancer in the population defined by the Surveillance, Epidemiology, and End Results cancer registries during 1992 to 1996. PATIENTS: 3 data sets were analyzed to assess the impact of surgeon volume on outcomes: 1) 24 166 colectomies performed by 2682 surgeons, 2) 10 737 prostatectomies performed by 999 surgeons, and 3) 2603 rectal resections performed by 1141 surgeons. MEASUREMENTS: Volume-outcome trends were analyzed by a conventional method (logistic regression) and corrected for clustering. Two widely used statistical methods for analyzing clustered data, a random-effects model and generalized estimating equations, were used and compared, and the degree of clustering was presented graphically. RESULTS: Substantial clustering was observed in the analyses involving morbidity end points. The 2 statistical techniques produced noticeably different results in some analyses. CONCLUSIONS: The presence of clustering represents variations in outcomes among providers with similar volumes. Thus, in volume-outcome studies, the degree of clustering of outcomes should be characterized because it may provide insight into variations in quality of care.

Clinical Competence↗

PubMed1983

Clinical trials and statistical verdicts: probable grounds for appeal.

Conventional interpretation of clinical trials relies heavily on the classic p value. The p value, however, represents only a false-positive rate, and does not tell the probability that the investigator's hypothesis is correct, given his observations. This more relevant posterior probability can be quantified by an extension of Bayes' theorem to the analysis of statistical tests, in a manner similar to that already widely used for diagnostic tests. Reanalysis of several published clinical trials according to Bayes' theorem shows several important limitations of classic statistical analysis. Classic analysis is most misleading when the hypothesis in question is already unlikely to be true, when the baseline event rate is low, or when the observed differences are small. In such cases, false-positive and false-negative conclusions occur frequently, even when the study is large, when interpretation is based solely on the p value. These errors can be minimized if revised policies for analysis and reporting of clinical trials are adopted that overcome the known limitations of classic statistical theory with applicable bayesian conventions.

Aspirin↗

PubMed1999

[Epidemiology and risk factors of Alzheimer's disease].

Alzheimer's disease or dementia of the Alzheimer's type (AD/DAT) is one of the most common dementia conditions and it amounts to over 40-90% of dementia cases among elderly and old patients. Epidemiological studies in this area make a great contribution to the study of the etiology and risk factors of AD/DAT). The collaborative reanalysis of AD/DAT prevalence and incidence in EEC countries ("EURODERM" programme) shows that the overall European age-specific prevalence of AD does not differ greatly. There was an exponential increase in age-specific AD/DAT prevalence was found with age, as evidenced by the studies made in Russia. Sex-specific prevalence and incidence of AD/DAT are unclear since the fact that the condition more often occurs in elderly women than in men of the same age has not been confirmed. The data on risk factors obtained in cohort and case-control studies of AD/DAT have been analyzed. Progress in molecular genetics has identified 3 genes that are responsible for the occurrence of familial forms of the disease. The gene of apolipoprotein E on chromosome 19 is recognized to be the major genetic risk factor of late AD/DAT. The role of gene mutations in the trigger mechanisms of sporadic BA/DAT is also discussed. The environmental risk factors of AD/DAT include brain injury, viral infections, neutroxic chemicals, various immunological and hormonal disorders. The protective role of such factors as long-term use of nonsteroid antiinflammatory agents and estrogens is discussed. The involvement of nicotine dependence in the pathogenesis and the role of smoking as a possible protective factor are the subject of discussion. Such factors as education levels, occupation, stresses are widely discussed, although their role is considered to be controversial. The Russian study revealed the influence of chronic stress on AD development. The authors consider that chronic stress may play an important role in AD/DAT progression.

Aged↗

PubMed1995

Social context of HIV infection in Uganda.

Some of the important policy and research implications of accumulating HIV/AIDS data are being ignored because of the attraction of social science research focused on the "multiple sexual mechanism' of infection and transmission. Attention is drawn to the other policy and research issues relating to information on the timing of infection through a reanalysis of existing data on cumulative AIDS cases. The most urgent need is to supplement the mainstream research on risk groups with studies of the timing and circumstances of entry into sexual activity in the pre-teen years.

Adolescent↗

PubMed1999

Structural basis for the activity of two muconate cycloisomerase variants toward substituted muconates.

We have refined to 2.3 A resolution two muconate cycloisomerase (MCIase) variant structures, F329I and I54V, that differ from each other and from wild-type in their activity toward cis,cis-muconate (CCM) and substituted CCMs. The working and free R-factors for F329I are 17.4/21.6% and for I54V, 17.6/22.3% with good stereochemistry. Except for the mutated residue, there are no significant changes in structure. To understand the differences in enzymatic properties we docked substituted CCMs and CCM into the active sites of the variants and wild type. The extra space the mutations create appears to account for most of the enzymatic differences. The lack of other structural changes explains why, although structurally equivalent changes occur in chloromuconate cycloisomerase (CMCIase), the changes in themselves do not convert a MCIase into a dehalogenating CMCIase. Reanalysis of the CMCIase structure revealed only one general acid/base, K169. The structural implication is that, in 2-chloro-CCM conversion by CMCIase, the lactone ring of 5-chloromuconolactone rotates before dehalogenation to bring the acidic C4 proton next to K169. Therefore, K169 alone performs both required protonation and deprotonation steps, the first at C5 as in MCIase, and the second, after ring rotation, at C4. This distinguishes CMCIase from alpha/beta barrel isomerases and racemases, which use two different bases.

Binding Sites↗

PubMed1999

Cost-effectiveness analysis of oral ondansetron and prochlorperazine for preventing nausea and vomiting after moderately emetogenic chemotherapy.

The article reports a study comparing the cost-effectiveness of ondansetron tablets and prochlorperazine capsules in preventing nausea and vomiting after moderately emetogenic chemotherapy in an outpatient setting. A decision analysis model was constructed to compare the cost-effectiveness of the two antiemetics from the perspective of third party health care payers. Probability estimates of the model were derived from a reanalysis of data obtained from a clinical trial directly comparing the two antiemetics. Effectiveness was defined as the number of patients with no emetic episodes and no drug-related adverse events during the 3-day period after receiving chemotherapy. Cost-estimates were based on Average Wholesale Price for medications and national average for hospital services adjusted to 1996 U.S. dollars. Cost-effectiveness ratios for ondansetron and prochlorperazine were $261 and $268 per effectively treated patient, respectively. A series of sensitivity analyses were performed to identify the limits of generalizability of study results. Despite the initial price differential between the two antiemetics, ondansetron was more cost effective than prochlorperazine when the duration of therapy was shorter than 3 days, the total cost of rescue therapy per patient was more than $71, the treatment cost of adverse events was less than $24, the complete relief rate for ondansetron was greater than 58.9 percent, and the complete relief rate for prochlorperazine was less than 26.5 percent.

Administration, Oral↗

PubMed1999

Pre-T cell receptor signals are responsible for the down-regulation of Syk protein tyrosine kinase expression.

Thymocyte development proceeds through two critical checkpoints that involve signaling events through two different receptors, the TCR and the pre-TCR. These receptors employ two families of protein tyrosine kinases to propagate their signals, the Src and Syk families. Genetic and biochemical evidence has shown that the Src family kinases are critical for normal T cell maturation. ZAP-70, a Syk family kinase, has similarly been implicated as a critical component in thymocyte development. Although genetic evidence has suggested that Syk is involved during thymocyte development, a definitive study of Syk expression has not been performed. In this paper we report our reanalysis of Syk expression in subpopulations of murine and human thymocytes by intracellular staining and flow cytometry using anti-Syk mAbs. Syk is expressed at increased levels during the stages in which pre-TCR signaling occurs. Furthermore, Syk is down-regulated after the pre-TCR checkpoint has been passed. Syk may play an important role in thymic development during pre-TCR signal transduction. Finally, incomplete down-regulation of Syk expression was noted in human thymocytes, offering a possible explanation for the distinct phenotypes of mice and humans deficient in ZAP-70.

Animals↗

PubMed1999

[Duration of maternity leave and sick leave during pregnancy].

The aim of the project was to describe the reasons for sick leave during pregnancy. This article presents data on a subgroup of women on sick leave. The purpose of this reanalysis was to examine whether women with short maternity leave had longer sick leave during pregnancy. Pregnant women in a Danish County applying for sick leave in a year were consecutively included in the study. Data were obtained by questionnaires during 1991-1992. Women with rights to a longer maternity leave, obtained through collective bargaining, were mainly employed in occupational groups related to the public sector and were on sick leave significantly longer, than women with short maternity leave, obtained only through legislation. The diagnoses differed among the two groups. Data suggest unequal possibilities for obtaining pregnancy related sick leave, as women with longer predelivery leave and a more secure employment situation had significantly longer sick leave than other women.

Denmark↗

PubMed1999

Interventions targeted toward patients to increase mammography use.

The objective of this study was to determine the effects of patient-based mammography screening strategies. We performed a meta-analysis and included United States studies that met the following criteria: (a) randomized or concurrent control design; (b) defined outcomes; and (c) data available for reanalysis. Interventions were classified as behavioral, cognitive, or sociological and further categorized by the type of control group (active versus usual care), number of interventions, and mode of intervention (interactive versus static). Data were combined using DerSimonian and Laird random effects models to yield summary effect sizes. A total of 63 interventions in 43 studies met the inclusion criteria. Behavioral interventions increased screening by 13.2% [95% confidence interval (CI), 4.7-21.2] compared with usual care, and by 13.0% (95% CI, 8.7-17.4) when using multiple strategies and 5.6% (95% CI, 0.6-10.6) when using a single intervention compared to active controls. Cognitive interventions using generic education strategies had little impact on screening, but those that used theory-based education (e.g., health belief model) increased rates by 23.6% (95% CI, 16.4-30.1) compared with usual care. Sociological interventions also increased screening rates. Interventions using a theoretical framework were the most effective in increasing screening rates. The ability of these interventions to increase screening among subgroups and improve rates of ongoing screening, as well as the costs of these strategies, is unknown and is an important area for future research.

Adult↗

PubMed1999

Effectiveness of interventions designed to increase mammography use: a meta-analysis of provider-targeted strategies.

The objective of this study was to determine the effectiveness of interventions targeted at providers to enhance the use of mammography. We performed a meta-analysis and included United States studies that used a randomized or nonrandomized concurrent control design, had defined outcomes, and presented data that could be abstracted for reanalysis. Interventions were classified as behavioral, cognitive, or sociological and further categorized by the type of control group (active versus usual care). Data were combined using DerSimonian and Laird random effects models to yield summary effect sizes. Thirty-five studies met the inclusion criteria. All types of interventions targeted at providers were effective in increasing mammography rates. Behavioral interventions increased screening by 13.2% [95% confidence interval (CI), 7.8-18.4] as compared with usual care and by 6.8% (95% CI, 4.8-8.7) as compared with active controls. Cognitive intervention strategies improved mammography rates by 18.6% (95% CI, 12.8-24.4). Sociological interventions also had a similar magnitude of effect on screening rates (13.1% increase; 95% CI, 6.8-19.3). Interventions targeting both patients and providers were not significantly better at increasing screening than those targeting providers alone, and multiple approaches (e.g., behavioral and cognitive) were generally not more effective than a single approach. All interventions targeted at physicians were effective in increasing screening rates. Decisions to use a particular approach will depend on resources, expertise, feasibility, and cost effectiveness.

Adult↗

PubMed2000

Robust assessment of statistical significance in the use of unbound/intrinsic pharmacokinetic parameters in quantitative structure-pharmacokinetic relationships with lipophilicity.

The optimization of pharmacokinetic properties remains one of the most challenging aspects of drug design. Key parameters, clearance and volume of distribution, are multifactorial, which makes deriving structure-pharmacokinetic relationships difficult. The correction of clearance and volume of distribution for the unbound fraction in plasma is one approach taken that has enabled quantitative structure-pharmacokinetic relationships to be derived. Three published data-sets where unbound parameters have been correlated with lipophilicity have been reanalyzed. The reanalysis has shown that high correlation coefficients can be achieved without any true correlation in the data and can lead to misinterpretation of the ways in which lipophilicity influences pharmacokinetics. Randomization procedures are proposed as a more robust method of assessing significance.

Algorithms↗

PubMed2000

Leptin binding and binding capacity in serum.

BACKGROUND: Leptin, a hormone produced primarily by adipose tissue, is known to be present in serum as both monomeric (free) and higher molecular mass (bound) forms, but little is known about the nature of the bound forms or physiological variation in binding capacity. METHODS: A new method to quantify the free and bound forms was developed, based on HPLC separation and RIA quantification in chromatography fractions. Reanalysis of specimens after addition of exogenous leptin allowed direct determination of leptin-binding capacity and the degree of saturation of leptin-binding capacity. RESULTS: HPLC chromatography fractionated serum leptin into both the free form and as a broad peak of 59-130 kDa. Several experiments were conducted to validate the new method. The concentrations of bound leptin in serum were 0.45-3.94 micro/L, and they increased as total leptin (reflecting adiposity) increased in 24 lean and obese volunteers. Leptin was readily dissociated from the bound fraction by competition from exogenous leptin. Rechromatography of the bound fraction led to dissociation of leptin, which was promoted by warming the sera before chromatography. Leptin-binding capacity was 1.8-5.3 microg/L; binding capacity was nearly constant over a range of total leptin concentrations of 2-10 microg/L, and slowly increased at higher total leptin concentrations. Saturation of binding capacity was low (15%) at very low total leptin concentrations (<5 microg/L), but rose quickly to a plateau near 80% at higher total leptin concentrations. CONCLUSIONS: The new method facilitates measurement of free and bound fractions of serum leptin, and is the first method measuring leptin-binding capacity. These experiments demonstrate that the concentration of bound leptin and leptin-binding capacity vary physiologically, with binding/binding capacity increasing with adiposity. Except in very lean individuals, binding capacity is nearly completely saturated.

Adult↗

PubMed2000

Psychology without p values. Data analysis at the turn of the 19th century.

Although the fledgling psychology of 100 years ago was assertively empirical, there were no inferential statistics to guide psychologists' data analyses. However, 19th-century developments had left psychology with a rich array of techniques for analyzing and presenting data, some of which remain underutilized today. These include comparisons across replications, within-subject designs, reanalysis of data, analyses of factorial designs, and especially the use of tables and graphs. As the merits of hypothesis-testing statistics are debated at the turn of the 21st century, the history of data-handling practices can remind psychologists that there are many ways to overcome the current uniformity of statistical practice.

Data Interpretation, Statistical↗

PubMed2000

Maximum androgen blockade in advanced prostate cancer: an overview of the randomised trials. Prostate Cancer Trialists' Collaborative Group.

BACKGROUND: In advanced prostate cancer, androgen suppression (AS) by surgery or drugs controls testicular hormone secretion, and the further addition of an antiandrogen such as nilutamide, flutamide, or cyproterone acetate is referred to as maximum androgen blockade (MAB). The aim of this overview was to compare the effects on the duration of survival of MAB and of AS alone. METHODS: The collaborative meta-analysis of 27 randomised trials involved central reanalysis of the data on each of 8275 men (98% of those ever randomised in trials of MAB vs AS) with metastatic (88%) or locally advanced (12%) prostate cancer. Half were over 70 years of age, and follow-up was typically for about 5 years. FINDINGS: 5932 (72%) men have died; of the deaths for which causes were provided, about 80% were attributed to prostate cancer. 5-year survival was 25.4% with MAB versus 23.6% with AS alone, a non-significant gain of 1.8% (SE 1.3; logrank 2p=0.11). There was no significant heterogeneity in the treatment effect (MAB vs AS) with respect to age or disease stage. The results for cyproterone acetate, which accounted for only a fifth of the evidence, appeared slightly unfavourable to MAB (5-year survival 15.4% MAB vs 18.1% AS alone; difference -2.8% [SE 2.4]; logrank 2p=0.04 adverse), whereas those for nilutamide and flutamide appeared slightly favourable (5-year survival 27.6% MAB vs 24.7% AS alone; difference 2.9% [SE 1.3]; logrank 2p=0.005). Non-prostate-cancer deaths (although not clearly significantly affected by treatment) accounted for some of the apparently adverse effects of cyproterone acetate. INTERPRETATION: In advanced prostate cancer, addition of an antiandrogen to AS improved the 5-year survival by about 2% or 3% (depending on whether the analysis includes or excludes the cyproterone acetate trials), but the range of uncertainty as to the true size of this benefit runs from about 0% to about 5%.

Aged↗

PubMed2000

Prognosis with dementia in Europe: A collaborative study of population-based cohorts. Neurologic Diseases in the Elderly Research Group.

The effect of dementia on time to death and institutionalization in elderly populations is of importance to resource planning, as well as to patients and their carers. The authors report a collaborative reanalysis of nine population-based studies conducted in Europe to compare dementia cases and noncases in risk of and time to death and to institutionalization. Prevalent and incident cases were more likely than noncases to reside in an institution at baseline and were more likely to enter institutional care. Prevalent cases also had over twice the risk of death compared to noncases and survival for men with dementia was consistently lower than that for women with dementia of the same age group.

Age Factors↗

PubMed2000

A look at the inheritance of height using regression toward the mean.

A reanalysis of the family growth study of Pearson and Lee (1903) leads to an explanation of the inheritance of height other than the one that has been offered until now. By acknowledging that the father may be incorrectly identified, this new analysis provides a more relevant explanation of the data: it fits parallel regression lines for sons and daughters, and is consonant with the theory that each parent contributes equally to the genetic makeup of their offspring, at least as far as height is concerned. The problem seems to lie in identifying the correct parents.

Age Distribution↗

PubMed2000

Is the sequencing of change processes by stage consistent across health problems? A meta-analysis.

Clinicians and researchers applying the transtheoretical model (J.O. Prochaska, C.C. DiClemente, & J.C. Norcross, 1992) to health promotion often assume that relationships of processes and stages observed in smoking cessation can be generalized to other problems. A reanalysis of 47 cross-sectional studies determined that use of change processes varies by stage, but the sequencing of processes is not consistent across health problems. In smoking cessation, cognitive processes were used in earlier stages than were behavioral processes. In exercise adoption and diet change, use of behavioral and cognitive processes increased together. Results for substance abuse and psychotherapy were less consistent. Substituting new behaviors, making a commitment, considering consequences, seeking information, controlling cues, and using rewards varied most by stage. Future longitudinal studies should assess these processes as potential mediators of lifestyle change.

Adaptation, Psychological↗

PubMed2001

Heart rate reactivity in male batterers: reply to Gottman (2001) and a second look at the evidence.

Together, the results of 3 studies examining heart rate reactivity (HRR) in male batterers do not provide strong support for the J. M. Gottman et al. (1995) batterer typology. All research groups found similar proportions of severely violent male batterers who show heart rate increases or decreases during a marital conflict discussion, but there was inconsistent validation of this taxonomy on variables of interest. This difference was also found among less violent and nonviolent men. The authors believe HRR may be useful for differentiating batterers on the dimension of anger-hostility but are less optimistic that HRR will reliably identify psychopathic or antisocial batterers. The authors do not agree that low levels of marital interaction conflict led to their failure to replicate. Reanalysis of data from J. C. Meehan, A. Holtzworth-Munroe, and K. Herron (2001) suggests baseline artifacts may be an important determinant of HRR differences. Methodological changes may improve the reliability of HRR assessment.

Adult↗