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PubMed2000

Stratified tests, stratified slopes, and random effects models for clinical trials with missing data.

Because missing observations may affect the size and power of statistical tests of equality, various analytical techniques explicitly or implicitly condition the analysis on the amount of information available per person. We illustrate the difference between stratifying a slope estimate and stratifying a test statistic based on slopes. We compare a nonparametric version of the latter approach with the parametric tests available from SAS Proc Mixed. Power and size of these two approaches are considered under different parametric settings, distributions, and missing data mechanisms.

Algorithms↗
PubMed2006

Meta-analysis for microarray studies of the genetics of complex traits.

In comparison to other complex disease traits, alcoholism and alcohol abuse are influenced by the combined effects of many genes that alter susceptibility, phenotypic expression and associated morbidity, respectively. Many genetic studies, in both animal models and humans, have identified genetic intervals containing genes that influence alcoholism or behavioral responses to ethanol. Concurrently, a growing number of microarray studies have identified gene expression differences related to ethanol drinking or other ethanol behaviors. However, concerns about the statistical power of these experiments, combined with the complexity of the underlying phenotypes, have greatly hampered the identification of candidate genes underlying ethanol behaviors. Meta-analysis approaches using recent compilations of large datasets of microarray, behavioral and genetic data promise improved statistical power for detecting the genes or gene networks affecting ethanol behaviors and other complex traits.

Alcohol Drinking↗
PubMed1991

Secular changes in published clinical trials of second-line agents in rheumatoid arthritis.

The present investigation was undertaken to explore changes over time in the design and reporting of trials of second-line drugs in rheumatoid arthritis, in the characteristics of patients included in the trials, and in the sources of funding. We studied 105 trials of second-line agents for the treatment of rheumatoid arthritis, including placebo-controlled and comparative trials involving 8 different agents. Three time periods, 1945-1969, 1970-1979, and 1980-1989, were compared. We found little change in the standards for reporting on the design of trials or for reporting information on patient dropout and drug side effects, some increase in the complexity of the statistical methods used, but no increase in the use of power analysis (reported in only 13% of trials). The average age of patients in clinical trials has increased. In recent years, there has been a substantial shift from placebo-controlled to comparative trials, and it is increasingly common for trials to be financially supported by pharmaceutical companies. The possible effects of secular trends should be considered when combining or comparing results of trials conducted in different years.

Age Factors↗
PubMed2001

Prognosis of patients with recurrent laryngeal carcinoma.

BACKGROUND: Although recurrent laryngeal carcinoma is a common clinical problem, the data regarding its natural history and prognostic factors are limited. The aim of the study was to describe the clinical course of patients with recurrent laryngeal carcinoma and determine the impact of various factors on their survival. METHODS: The medical files of 65 patients with recurrent laryngeal cancer treated at the Rabin Medical Center between 1975 and 1996 were reviewed. The possible risk factors for survival were analyzed using univariate and multivariate models. RESULTS: The estimated 2- and 5-year survival rates of the patient population were 67% and 56%, respectively. On univariate analysis, primary tumor site, T stage and nodal status, duration of disease-free interval, site of recurrence, and operability of recurrent tumor were all powerful prognostic factors for survival. On multivariate analysis, three variables retained statistical significance: primary tumor site (p < .001), site of recurrence (p < .001), and its operability (p = .005). CONCLUSIONS: We found several disease-related factors to be predictive of poor outcome in patients with recurrent laryngeal cancer. Our data emphasize the need for early detection not only of primary tumors but also of their recurrences.

Adult↗
PubMed1994

The effect of LDL apheresis on progression of coronary artery disease in patients with familial hypercholesterolemia. Results of a multicenter LDL apheresis study.

This study investigated the effect of extracorporal lipid-lowering therapy by low-density lipoprotein (LDL) apheresis on coronary artery disease in a population characterized by early development and rapid progression of atherosclerosis. We treated 32 patients aged between 15 and 63 years with drug-refractory familial hypercholesterolemia, treated once a week by immuno-specific LDL apheresis for 3 years in a controlled prospective and non-randomized trial; 25 patients (14 females and 11 males) completed the study. Noninvasive data were obtained by physical examination, 12-lead ECG and exercise testing. Invasive cardiological data were obtained by cardiac catheterization according to a standardized protocol in four cardiological centers. Left ventricular ejection fraction was calculated using planimetry. Coronary stenoses were measured quantitatively in 23 defined coronary segments by a panel of four investigators with an electronic digital caliper. In addition, overall coronary atherosclerosis was visually qualified. Final decisions on a classification into one of three groups (regression, no change, progression) of coronary atherosclerosis were based on panel consensus. Six cardiac events occurred throughout the study: percutaneous transluminal coronary angioplasty in one patient, coronary bypass grafting in three and two deaths. Statistical analysis of exercise testing yielded no significant change for maximum power and work capacity during the study period. Hemodynamic data revealed no significant change; mean ejection fraction was calculated as 65.8 +/- 15.9% at study entry and 67.0 +/- 12.7% at completion. Quantitative measurement of 111 circumscribed coronary stenoses showed a mean stenosis degree of 45 +/- 26% at entry cineangio-film and 43 +/- 22% at final cineangio-film demonstrating no significant change.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Gamma-aminobutyric acid modulates chloride channel activity in cultured primary bovine lactotrophs.

The effects of GABA, the analogues muscimol and baclofen, and the antagonist bicuculline were investigated on cultured primary bovine lactotrophs using the patch clamp technique. Under voltage clamp in the whole cell mode using solutions containing chloride as the only permeable ion, GABA application increased the amplitude of mean membrane current and fluctuations of current about this mean. Statistical analysis of current fluctuations induced by GABA showed that the power density spectra in 8 of 12 cells were best fitted to double Lorentzian functions and the variance was smallest around the estimated equilibrium potential of chloride ions. The underlying channel open time estimated from noise analysis was only weakly voltage-dependent. The variance of current noise increased with GABA concentration within the range of 1-30 microM, although a slight decrease of variance in one cell could be observed at 30 microM, suggesting that desensitization to GABA might occur. Muscimol mimicked the effect of GABA but baclofen was without effect under these conditions. Bicuculline reduced the GABA-activated membrane current fluctuations. GABA- or muscimol-activated channels recorded in isolated outside-out patches had a slope conductance of about 20 pS. Mean open times of the channel were characterized by two exponential decay functions. We conclude that bovine lactotrophs have GABA-activated chloride channels, which appear to be voltage-independent. In addition, the action of GABA appears to be mediated through the GABAA receptor subtype.

Animals↗
PubMed2026

Association between the interleukin 17F rs763780 polymorphism and immune thrombocytopenia risk: A systematic review and meta-analysis.

The literature on the Interleukin 17F (IL-17F) rs763780 polymorphism and its association with immune thrombocytopenia (ITP) risk remains inconsistent and controversial. These uncertainties underscore the urgent need for a meta-analysis to objectively synthesize the heterogeneous findings, mitigate bias, and improve statistical power. This study strictly adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement and guidelines. A systematic literature search for original studies was conducted across the CNKI, Wanfang Data, Cochrane Library, Web of Science, and PubMed databases, covering publications up to April 5, 2026. Odds ratios and corresponding 95% confidence intervals were calculated to assess the association. STATA 14.2 software was used to synthesize the pooled estimates. A total of eight case-control studies consisting of 805 ITP cases and 841 controls were included. The summarized statistics suggested the detrimental effect of the A allele in the homozygote and recessive models. In the sensitivity analysis, the results that were initially non-significant in the allele, heterozygote, and dominant models became significant after excluding a single dataset, which was also identified as the source of heterogeneity. Region-stratified analyses revealed statistical significance in the Chinese/Japanese and Egyptian subgroups under specific analytic contrasts. When stratified according to age, the children subgroup showed significant associations in a subset of genetic models, while the adult counterpart demonstrated significance across all models. In conclusion, the pooled estimates of the homozygote and recessive models suggested that the rs763780 polymorphism is associated with ITP risk, but this finding requires further validation through large-scale studies.

Humans↗
PubMed2005

Effects of incomplete chest wall decompression during cardiopulmonary resuscitation on coronary and cerebral perfusion pressures in a porcine model of cardiac arrest.

INTRODUCTION: Recent data suggest that generation of negative intrathoracic pressure during the decompression phase of CPR improves hemodynamics, organ perfusion and survival. HYPOTHESIS: Incomplete chest wall recoil during the decompression phase of standard CPR increases intrathoracic pressure and right atrial pressure, impedes venous return, decreases compression-induced aortic pressures and results in a decrease of mean arterial pressure, coronary and cerebral perfusion pressure. METHODS: Nine pigs in ventricular fibrillation (VF) for 6 min, were treated with an automated compression/decompression device with a compression rate of 100 min(-1), a depth of 25% of the anterior-posterior diameter, and a compression to ventilation ratio of 15:2 with 100% decompression (standard CPR) for 3 min. Compression was then reduced to 75% of complete decompression for 1 min of CPR and then restored for another 1 min of CPR to 100% full decompression. Coronary perfusion pressure (CPP) was calculated as the diastolic (aortic (Ao)-right atrial (RA) pressure). Cerebral perfusion pressure (CerPP) was calculated multiple ways: (1) the positive area (in mmHg s) between aortic pressure and intracranial pressure (ICP) waveforms, (2) the coincident difference in systolic and diastolic aortic and intracranial pressures (mmHg), and (3) CerPP = MAP--ICP. ANOVA was used for statistical analysis and all values were expressed as mean +/- S.E.M. The power of the study for an alpha level of significance set at 0.05 was >0.90. RESULTS: With CPR performed with 100%-75%-100% of complete chest wall recoil, respectively, the CPP was 23.3 +/- 1.9, 15.1 +/- 1.6, 16.6 +/- 1.9, p = 0.003; CerPP was: (1) area: 313.8 +/- 104, 89.2 +/- 39, 170.5 +/- 42.9, p = 0.03, (2) systolic aortic minus intracranial pressure difference: 22.8 +/- 3.6, 16.5 +/- 4, 23.7 +/- 4.5, p = n.s., and diastolic pressure difference: 5.7 +/- 3, -2.4 +/- 2.4, 3.2 +/- 2.5, p = 0.04 and (3) mean: 14.3 +/- 3, 7 +/- 2.9, 12.4 +/- 2.9, p = 0.03, diastolic aortic pressure was 28.1 +/- 2.5, 20.7 +/- 1.9, 20.9 +/- 2.1, p = 0.0125; ICP during decompression was 22.8 +/- 1.7, 23 +/- 1.5, 19.7 +/- 1.7, p = n.s. and mean ICP was 37.1 +/- 2.3, 35.5 +/- 2.2, 35.2 +/- 2.4, p = n.s.; RA diastolic pressure 4.8 +/- 1.3, 5.6 +/- 1.2, 4.3 +/- 1.2 p = 0.1; MAP was 52 +/- 2.9, 43.3 +/- 3, 48.3 +/- 2.9, p = 0.04; decompression endotracheal pressure, -0.7 +/- 0.1, -0.3 +/- 0.1, -0.75 +/- 0.1, p = 0.045. CONCLUSIONS: Incomplete chest wall recoil during the decompression phase of CPR increases endotracheal pressure, impedes venous return and decreases mean arterial pressure, and coronary and cerebral perfusion pressures.

Animals↗
PubMed2000

Multi-night exposure to 60 Hz magnetic fields: effects on melatonin and its enzymatic metabolite.

Magnetic field-induced suppression of nocturnal melatonin in humans has been reported in occupational and residential studies, but not in laboratory-based exposure studies. The present study examined whether this contrasting pattern of results might be related to associated differences in exposure duration or to field-induced measurement instability over time. Thirty healthy young men were evaluated using a randomized, double-blind test protocol. Statistical analysis indicated that 4 consecutive nights of exposure to power-frequency magnetic fields at occupational intensity (resultant flux density = 28.3 microtesla, muT, [283 milligauss, mG]) had no differential effect on concentrations of melatonin or its major enzymatic metabolite (6-hydroxymelatonin sulfate, 6-OHMS) in daily morning urine samples, compared to equivalent no-exposure sham control conditions. The consistency of intra-individual urinary measurements over the 4 test nights also was quite high (P < 0.01) in the sham control condition. In contrast, repeated nightly exposure to the magnetic field was associated with reduced consistency. Morning urinary measures obtained after exposure on night 4 differed (P < 0.01) from similar measures obtained after the second and third exposure night. Thus, while the overall results of this study do not support the melatonin hypothesis, there is some suggestion of a possible cumulative effect of magnetic field exposure on the stability of individual melatonin measurements over time. Additional research with longer periods of controlled exposure may be warranted.

Adolescent↗
PubMed1987

Is ventilatory anaerobic threshold a good index of endurance capacity?

This study was undertaken to assess whether ventilatory anaerobic threshold (T vent) reflected endurance capacity (EC) in sports medical control. Fifteen subjects performed two cycle ergometer tests. The first was a maximal exercise test, which consisted of increasing the load 20 W/min until exhaustion. During this test, the gas exchange anaerobic threshold was determined and VO2 max was measured. The second was an endurance exercise test, which consisted of asking the subject to work, as long as possible, a load representing 80% of his maximal aerobic power. During this test, we measured endurance time (ET). The statistical analysis showed the lack of relationship between VO2 max and ET and the linear correlations between VO2 T vent ml/min/kg and ET min (r = 0.521, P less than 0.05), VO2 T vent l/min and ET min (r = 0.524, P less than 0.05), and T vent % VO2 max and ET (r = 0.738, P less than 0.01). These results establish that ventilatory anaerobic threshold actually reflects endurance capacity. This relation can be explained referring to the muscle energetic metabolism during exercise. Therefore, T vent should be determined systematically in addition to VO2 max during maximal exercise tests to better evaluate physical fitness.

Adolescent↗
PubMed2004

Genetic association studies in mood disorders: issues and promise.

Genetic association is a powerful method for identifying genetic variants that contribute to the molecular basis of complex diseases. There is now a wealth of informative, validated and densely-spaced single nucleotide polymorphism (SNP) markers for use in association studies, and the delineation of the genome-wide haplotype architecture will greatly enhance our ability to conduct whole genome association screens, fine mapping of linkage regions, and systematic screening of functional candidate genes. Single nucleotide polymorphism-based genotyping technology has progressed dramatically to the point of high-throughput methods that can assay up to thousands of SNPs on many samples in one experiment. Genotyping cost remains a limiting factor in complex disease studies, where numerous SNPs and large sample sets are needed to maximize statistical power. Strategies designed to reduce cost include DNA pooling and analysis with tagSNPs. As larger clinical samples become available, it will be increasingly important to test for hidden stratification in case-control studies, as well as transmission distortion in family-based studies, either of which can lead to spurious association findings. As yet, there is no widely-accepted genetic association finding in mood disorders, but functional candidate genes, such as the serotonin transporter, and positional candidates, such as G72/G30 on chromosome 13q, are beginning to be identified in several studies. Relating associated variants to the phenotype represents the next critical step toward establishing the pathogenic role of gene variants in mood disorders.

Gene Pool↗
PubMed2006

Quasi-empirical Bayes methodology for improving meta-analysis.

This article addresses the problem of heterogeneity among various studies to be combined in a meta-analysis. We adopt quasi-empirical Bayes methodology to predict the odds ratios for each study. As a result, the predicted odds ratios are pulled toward the estimated common odds ratio of the various studies under consideration. With strong heterogeneity among the studies, we jointly consider the display of the 95% CIs of the ORs and a Dixon's test (1950) for "outliers" to exclude the "extreme" estimated ORs. We demonstrate the effectiveness of our methodology based on the data analyzed by Thompson and Pocock (1987) demonstrating the power of the new approach to meta-analysis to find statistical agreement in what looks like great disagreement via a chi-squared test. We believe our technique (i.e., minimum mean-square sense) will go a long way toward increasing the trustworthiness of meta-analysis.

Bayes Theorem↗
PubMed2003

The German multicenter, randomized, partially blinded, prospective trial of acupuncture for chronic low-back pain: a preliminary report on the rationale and design of the trial.

BACKGROUND: The efficacy of acupuncture treatment for chronic low-back pain has not been reliably proven because of a lack of good quality studies, leading to the necessity of developing the German Acupuncture Trial for Chronic Low-Back Pain (GERAC-cLBP) study. OBJECTIVE: The aim is to assess the effectiveness of traditional Chinese acupuncture for chronic low-back pain compared to sham acupuncture and with a conventional standard therapy. METHODS: This trial is a nationwide, multicenter, randomized, prospective, partially blinded study. The primary endpoint is the success rate after 6 months. Success is defined as an improvement of 33% or more of three pain-related items on the Van-Korff Pain Score or an improvement of 12% or more in the disability measured by the Hanover Functional Ability Questionnaire. Assessment of the effectiveness of the blinding of patients to the form of acupuncture they received will be conducted. All clinical endpoints are assessed centrally by blinded independent observers. The sample size, with a total of 1062 patients to be enrolled, is based on power calculations. Independent central randomization, data collection, data processing, and statistical analysis are provided. Success rates will be tested for differences using two-sided Fisher exact tests. In the primary analysis, all tests will be carried out on the basis of the intention-to-treat principle. Secondary analyses will be conducted according to protocol approaches. TRIAL STATUS: The pilot phase of the trial started in February 2002, the estimated duration of the study is 2.5 years. Enrollment is anticipated to be completed in the winter of 2003. CONCLUSION: The GERAC-cLBP study is currently the world's largest controlled trial of the effectiveness of acupuncture treatment for low-back pain. It will contribute to the evaluation of efficacy by means of evidence based medicine.

Acupuncture Therapy↗
PubMed2003

Partial regression of primary cutaneous melanoma: is there an association with sub-clinical sentinel lymph node metastasis?

Whether partial regression of a primary melanoma has an adverse impact on prognosis is controversial. As an indirect mechanism of addressing this question we drew a correlation between the histopathological characteristics of 107 cutaneous melanomas and the presence of sub-clinical metastasis in corresponding sentinel lymph nodes. Partial regression of the primary tumor, defined as focal replacement of the lesion by a scar, unrelated to a previous biopsy, was observed in 20 (19%) cases in the group as a whole. Excluding cases in which an accurate Breslow thickness of the primary melanoma could not be established and/or the presence of a capsular nevus was detected in the sentinel node, a total of 97 remained. Seventeen cases (Breslow thickness 0.63-9.7; mean 2.4 mm) showed partial regression and 80 (Breslow thickness 0.25-7.00; mean 1.8 mm) were devoid of regression. Of the 17 cases with regression 5 (29%) had nodal metastasis (by histopathology and/or molecular analysis) and of the 80 cases without regression 23 (29%) had nodal metastasis (by one or both evaluations). Our data reveals no association between partial regression of the primary melanoma and sentinel node involvement by the disease. The Breslow thickness proved to be the only significant independent variable related to nodal metastasis. Of interest, ulceration of the primary lesion was significantly associated with nodal disease on univariate, but not on multivariate, analysis. While acknowledging that the cohort size may lack the statistical power to demonstrate subtle associations, our data supports the known relevance of tumor thickness and ulceration to regional lymph node metastasis and thereby, to outcome of melanoma in its early stages, but fails to support a similar role for partial regression.

Adult↗
PubMed2006

Impact of prior abdominal or pelvic surgery on colonoscopy outcomes.

GOALS: This large prospective study attempted to analyze the effect of various prior surgery on colonoscopy performance. BACKGROUND: It is generally presumed that colonoscopy in patients with a history of abdominal or pelvic surgery is difficult. This difficulty is apparently due to adhesions and anatomic alterations after surgery but the incidence, site, and severity of adhesions are different according to the types of surgery. STUDY: We analyzed completion rate and insertion time in 4089 consecutive colonoscopies in patients with intact colon. RESULTS: The adjusted completion rate for colonoscopy was 96.7%. The mean insertion time was 6.2+/-4.0 minutes. Not only old age [odds ratio (OR) 1.46; 95% confidence interval (CI) [1.04, 2.04]] and inadequate bowel cleansing (OR 5.82; 95% CI [4.19, 8.09]) but also a surgical history (OR 1.71; 95% CI [1.18, 2.48]) were independent factors associated with procedural incompleteness. Of surgical history, gastrectomy and hysterectomy were significantly associated with procedural incompleteness (P<0.001 and P=0.001, respectively). Old age (OR 1.48; 95% CI [1.22, 1.79]), female sex (OR 1.22; 95% CI [1.01, 1.48]), constipation as an indication (OR 1.58; 95% CI [1.24, 2.02]), and inadequate bowel cleansing (OR 1.46; 95% CI [1.13, 1.88]) were independent factors associated with prolonged insertion time (>10 min), but a surgical history lost statistical power as a predictor for prolonged insertion time in multivariate analysis. CONCLUSIONS: Although the difference in insertion time was not substantial, a history of abdominal or pelvic surgery is associated with difficulty in colonoscopy.

Abdomen↗
PubMedDate not supplied

Writing a grant proposal--part 2: research methods--part 2.

As part of a Spotlight series on grant writing by members of the Center for Clinical Investigation of the Wound Ostomy and Continence Nursing (WOCN) Society, this article completes an explanation about writing the Methods section of a grant proposal. The aim of this series is to enhance the skills of WOC nurses to increase submissions of high-quality grants related to WOC nursing science and success in garnering funding, particularly from foundation grants, such as that of the WOCN. In this article, writing about the sample and setting, power analysis, sampling and recruitment procedures, implementation and data collection procedures, statistical analysis plan, and ethical considerations are described.

Data Collection↗
PubMed2004

Cerebrovascular hemodynamics in pregnant women with mild chronic hypertension.

OBJECTIVE: To evaluate and compare the cerebrovascular autoregulation in pregnant normotensive and mild chronic hypertensive patients without preeclampsia. METHODS: Transcranial Doppler ultrasound was used to measure peak, end-diastolic, and mean velocities in the middle cerebral arteries of 34 normotensive and 17 mild chronic hypertensive women in the third trimester of pregnancy. Measurements were performed in the left lateral position at baseline, during 5% CO(2) inhalation, and during an isometric handgrip test. Mean pulsatility index, resistance index, and cerebral perfusion pressure at each time were compared using 2-way repeated measures analysis of variance. Using an alpha error of 5%, the statistical power to identify differences in middle cerebral artery indices in response to the two maneuvers was at least 90% and 50% in comparison between the two groups. Significance was P <.05. RESULTS: Pregnant women with mild chronic hypertension had higher baseline mean blood pressure but similar pulsatility index (0.73 versus 0.75), resistance index (0.50 versus 0.50), and cerebral perfusion pressure (59.9 versus 61.8 mm Hg) compared with normotensive pregnant women. Both maneuvers caused a significant reduction in pulsatility index and resistance index and higher cerebral perfusion pressure. No significant differences were noted in the response to either 5% CO(2) inhalation or isometric handgrip test between the two groups. CONCLUSION: Pregnant women with mild chronic hypertension show normal cerebral vasomotor reactivity to CO(2) breathing and isometric handgrip. This suggests that the abnormal cerebrovascular autoregulation in preeclampsia is not directly linked to the elevated blood pressure but rather is determined by a separate pathophysiologic pathway. LEVEL OF EVIDENCE: II-2

Adult↗
PubMed2006

The importance of analyzing graft and patient survival by cause of failure: an example using pediatric small intestine transplant data.

BACKGROUND: Although graft and patient survival are vital in reporting overall results of clinical transplant studies, these outcomes do not account for distinct types of graft failure and death, which clearly exist in pediatric small intestine transplantation (Itx). The use of a cause-specific hazard (CSH) approach may provide more precise identification and thus greater insight as to why certain factors are prognostically important. METHODS: Among 119 pediatric patients who received primary Itx at our center since 1994, Cox model stepwise regression analyses were performed to identify prognostic factors for the following CSH rates: intestinal graft failure (IGF)/death due to rejection, death due to infection not triggered by IGF, and intestinal graft loss/death due to other causes. RESULTS: Two factors were associated with a significantly higher rate of developing IGF due to rejection (23 such failures): receiving an isolated intestine or liver-intestine transplant (P=0.00001) and receiving no induction agent (P=0.006). Conversely, age at transplant <1 year was the single factor associated with a significantly higher death rate due to infection (P=0.0005) (21 such deaths). Two characteristics were associated with a significantly higher death rate due to other causes: being in the hospital pretransplant (P=0.007) and not receiving daclizumab induction therapy (P=0.02) (24 such deaths). Although these four factors (transplant type/age/hospital status/induction therapy) were, for the most part, associated with graft/patient survival, the CSH analysis more precisely identified their prognostic value and achieved greater statistical power. CONCLUSIONS: A CSH approach should be used in conjunction with overall outcome analyses.

Cohort Studies↗