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Possible Confounding Variables (possible + confounding_variable)
Selected AbstractsUsing propensity scores to estimate the effects of insecticides on stream invertebrates from observational data,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2009Lester L. Yuan Abstract Analyses of observational data can provide insights into relationships between environmental conditions and biological responses across a broader range of natural conditions than experimental studies, potentially complementing insights gained from experiments. However, observational data must be analyzed carefully to minimize the likelihood that confounding variables bias observed relationships. Propensity scores provide a robust approach for controlling for the effects of measured confounding variables when analyzing observational data. Here, we use propensity scores to estimate changes in mean invertebrate taxon richness in streams that have experienced insecticide concentrations that exceed aquatic life use benchmark concentrations. A simple comparison of richness in sites exposed to elevated insecticides with those that were not exposed suggests that exposed sites had on average 6.8 fewer taxa compared to unexposed sites. The presence of potential confounding variables makes it difficult to assert a causal relationship from this simple comparison. After controlling for confounding factors using propensity scores, the difference in richness between exposed and unexposed sites was reduced to 4.1 taxa, a difference that was still statistically significant. Because the propensity score analysis controlled for the effects of a wide variety of possible confounding variables, we infer that the change in richness observed in the propensity score analysis was likely caused by insecticide exposure. [source] The role of quality of care in health-related quality of life in patients with IBDINFLAMMATORY BOWEL DISEASES, Issue 4 2004Ingrid van der Eijk PhD Abstract In the literature there are indications of associations between health-related quality of life (HRQoL) in inflammatory bowel disease and disease activity, psychological status, coping, stressful life events, and social support. The aim of this study was to examine whether a relation exists between quality of health care and HRQoL, taking possible confounding variables into account. For this purpose, one single questionnaire was compiled from existing validated questionnaires. A population-based inception cohort of 1056 patients with inflammatory bowel disease in eight countries, diagnosed 6 to 8 years prior to the study, was approached to participate. In total, 824 patients responded (78%), and 517 could be included in statistical analyses. It was shown that in inflammatory bowel disease HRQoL was indeed influenced by quality of care (particularly with regard to the parameters of "providing information," "costs," and "courtesy"), as well as by disease activity, psychological status, type of hospital, social support, stressful life events, and way of administration of the questionnaire. Patients with active disease had lower psychological status and HRQoL scores at the time of the survey than patients without active disease. However, quality of care scores did not differ between these groups. The care aspect "costs" was scored worse by CD compared with UC patients, probably caused by a potentially more expensive treatment. In conclusion, it is shown in a large exploratory study, for the first time, that in inflammatory bowel disease, quality of care has a significant role in determining health-related quality of life. [source] Body Mass Index But Not Pulse Pressure Is Associated with Lesser Penile,Vaginal Intercourse Frequency in Healthy Young MenTHE JOURNAL OF SEXUAL MEDICINE, Issue 5 2010Stuart Brody PhD ABSTRACT Introduction., A growing literature links aspects of sexual and cardiovascular function. Recent research revealed that pulse pressure (systolic minus diastolic) was associated with poorer erectile function (and hypogonadism) in male patients with erectile dysfunction. It is unclear to what degree pulse pressure (and body mass index) would be associated with aspects of sexual function in a younger, healthy sample (controlling for possible confounders). Aims., To examine the associations of frequency of specific sexual behaviors with both resting pulse pressure and body mass index. Methods., Sixty-five healthy young men (mean age 25.2 ± 4.6 years) had their resting blood pressure, weight, and height recorded, and reported the frequency of their various sexual activities. Main Outcome Measures., Correlations of pulse pressure with different sexual behaviors (univariate and adjusted for possible confounding variables including age, mean blood pressure, body mass index, social desirability responding score, and cohabitation status). Results., For these healthy young men, on univariate and adjusted analyses, pulse pressure was not significantly associated with frequencies of penile,vaginal intercourse, other partnered sexual activity, or masturbation. In contrast, body mass index was associated with lesser frequency of penile,vaginal intercourse but not other sexual behaviors. Conclusions., The association of pulse pressure with sexual function previously observed in older men was not observed in this younger healthy sample. Other measures of arterial stiffness might be indicated in a healthy young population. Even within the normal range and adjusted for possible confounders, increasing body mass index (a rough proxy for body fat) is associated with reduced frequency of specifically penile,vaginal intercourse, which might be a result of some combination of characterological and hormonal factors. Brody S. Body mass index but not pulse pressure is associated with lesser penile,vaginal intercourse frequency in healthy young men. J Sex Med 2010;7:1853,1857. [source] The protective effect of antimalarial drugs on thrombovascular events in systemic lupus erythematosusARTHRITIS & RHEUMATISM, Issue 3 2010Hyejung Jung Objective The antimalarial medication hydroxychloroquine has been proposed as a thromboprotective agent in systemic lupus erythematosus (SLE), but studies thus far have been limited by the possibility of confounding by indication. This study was conducted to assess whether exposure to antimalarial drugs is associated with a decrease in thrombovascular events (TEs) in patients with SLE. Methods The study was designed as a nested case,control study embedded in an inception cohort of patients with SLE, which allowed adjustments for possible confounding by calendar year, duration of disease, duration of observation, and severity of lupus. After controlling for the possible confounding variables in conditional logistic regression models, the use of antimalarial drugs was assessed for its effects on the development of TEs in lupus patients. Results Fifty-four cases of TE were identified, and these were matched with 108 control subjects (lupus patients without TEs). Univariate analyses identified older age (odds ratio [OR] 1.04, 95% confidence interval [95%CI] 1.01,1.07) or being older than age 50 years (OR 3.5, 95% CI 1.4,8.6) and ever having hypertension (OR 2.5, 95% CI 1.0,5.8) as being associated with an increased risk of TEs, whereas use of antimalarial drugs (OR 0.31, 95% CI 0.13,0.71) was associated with a decreased risk of TEs. Separate analyses were done for arterial and venous TEs, which yielded similar results. In multivariate analyses, use of antimalarial drugs (OR 0.32, 95% CI 0.14,0.74) and older age (OR 1.04, 95% CI 1.01,1.07) were the only 2 variables that remained significant. Conclusion The results from this nested case,control study demonstrate that, after accounting for the effects of disease severity, disease duration, and calendar year, antimalarial drugs were found to be thromboprotective, being associated with a 68% reduction in the risk of all TEs, with a range of risk reduction of at least 26% up to as high as 86%. [source] High plasma levels of factor VIII and risk of recurrence of venous thromboembolismBRITISH JOURNAL OF HAEMATOLOGY, Issue 4 2004Legnani Cristina Summary The aim of this study was to evaluate the relationship between factor VIII (FVIII) levels, measured by chromogenic and clotting assays, and risk of venous thromboembolism (VTE) recurrence. A total of 564 patients underwent clinical follow-up after oral anticoagulant withdrawal (total follow-up = 924·4 years). Recurrent VTE developed in 39 of 309 (12·6%) patients with a first idiopathic VTE and in 14 of 255 (5·5%) patients whose first event was secondary. In patients with a first idiopathic VTE, the risk of recurrence was more than fivefold higher in patients with FVIII levels exceeding the 90th percentile [chromogenic FVIII: relative risk (RR) 5·43 (95% CI 1·76,16·8); clotting FVIII: RR 6·21 (95% CI 1·57,24·5)] after adjustment for all possible confounding variables. In patients with a first secondary VTE, the risk of recurrence was slightly higher in patients with high FVIII levels [chromogenic FVIII: RR 2·62 (95% CI 0·34,19·9); clotting FVIII: RR 1·74 (95% CI 0·25,12·1)], but, given the low number of recurrences, the 95% CI were very large. In conclusion, this study shows that high FVIII levels are associated with increased risk of VTE recurrence in patients with a first idiopathic VTE. Although the measurement of FVIII levels by a specific chromogenic assay might, in principle, be preferred to avoid the risk of aspecific clotting effects, no significant differences in results obtained by chromogenic or clotting methods were found. [source] Association of p53 codon 72 polymorphism and MDM2 SNP309 with clinical outcome of advanced nonsmall cell lung cancerCANCER, Issue 4 2008Ji-Youn Han MD Abstract BACKGROUND. The purpose of the study was to investigate whether polymorphisms of p53 codon 72 (Arg72Pro) and MDM2 SNP309 (309T>G) affect p53 expression and the clinical outcome of patients with advanced nonsmall cell lung cancer (NSCLC). METHODS. A total of 148 NSCLC patients, previously enrolled in 2 different prospective clinical trials, were genotyped for the p53 Arg72Pro and MDM2 309T>G polymorphisms. Immunohistochemical staining of p53 protein was performed on 61 tumor samples. Genotypes were correlated with p53 expression, clinicopathologic factors, tumor response, and survival. Multivariate logistic or Cox regression analyses were used to adjust for possible confounding variables. RESULTS. The distribution of sex, age, performance status, stage, tumor histology, and smoking habit was not significantly different among polymorphism variants. However, a significant association was observed between p53 Arg72Pro polymorphism and primary resistance to chemotherapy. Patients with the Pro/Pro variant were more likely to be resistant to first-line chemotherapy, especially the irinotecan plus cisplatin regimen, than those with Arg/Arg or Arg/Pro variants (60% vs 27%, P = .014). In multivariate analysis, the Pro/Pro genotype was strongly predictive for shorter progression-free survival (PFS) (hazard ratio [HR] = 1.952, P = .01). The p53 overexpression was associated with MDM2 SNP309. The TT genotype showed more p53 overexpression than TG or GG genotypes (P = .036). In multivariate analysis, the MDM2 TT genotype was independently predictive for longer survival (HR = 1.742, P = .032). CONCLUSIONS. The p53 72Pro/Pro variant was predictive for primary resistance to chemotherapy and shorter progression-free survival. The MDM2 SNP309 was associated with less p53 overexpression and prognostic for worse survival. Genotyping these polymorphisms may be useful for predicting the clinical outcome of advanced NSCLC. Cancer 2008. © 2008 American Cancer Society. 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