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PubMed2004

Complete dentures and oral health-related quality of life -- do coping styles matter?

UNLABELLED: Oral health-related quality of life (OHRQOL) in edentulous patients with complete dentures is often impaired. This paper investigates the effect of different coping styles on OHRQOL. PURPOSE: (a) To assess OHRQOL of edentulous patients with conventional complete dentures, and (b) to investigate if individual differences in these patients' styles of coping with stress affect their OHRQOL. MATERIALS AND METHODS: Data were collected from 249 fully edentulous patients with complete dentures (mean age: 66.0 years) who responded to a mailed survey (adjusted response rate: 48.8%). OHRQOL was measured with the 14-item short form of the oral health impact profile (OHIP). Ratings of coping strategies were obtained using the 28-item Brief COPE, an instrument measuring various styles of coping with stress. Linear regression analyses were used to explore the relationships between coping styles, background variables such as age, gender, income, and age of prosthesis, and the patients' OHRQOL. RESULTS: About 35% of the respondents reported impacts from their oral conditions on their overall OHRQOL (OHIP-14 total score) occasionally, fairly often, or often. Physical pain was even more prevalent, with 53.3% of the respondents reporting pain impacts. The linear regression model (P < 0.0001) explained 31.1% of the variation in the OHIP-14 total score. The coping variables instrumental support, behavioral disengagement, substance abuse, denial, and religion were significant negative predictors of OHRQOL. Only emotional support was a significant positive predictor of OHRQOL. CONCLUSION: Wearing conventional complete dentures has a significant impact on OHRQOL. This impact is moderated by the styles a patient uses to cope with stress. Using emotional support has a positive effect on OHRQOL, while other coping styles, namely instrumental support, behavioral disengagement, substance abuse, denial, and religion are significant negative predictors of OHRQOL.

Adaptation, Psychological↗

PubMed2002

Metabonomic assessment of physiological disruptions using 1H-13C HMBC-NMR spectroscopy combined with pattern recognition procedures performed on filtered variables.

Metabonomic characterization of long-lasting although weak physiological events such as anabolic disruptions remains poorly investigated. We have validated 1H-13C HMBC-NMR as a suitable generator of instrumental variables that are strongly linked to the concentration of endogenous metabolites in biological fluids. This method is interfaced to multivariate pattern recognition procedures. Fingerprints established from urine sample collected on cattle treated with anabolic steroids were used to validate this method. Four main results arise from this study. (i) 2D NMR is as informative as 1D NMR. (ii) 2D NMR variable clustering highlights successfully a contingent redundancy of variables, although a relevant hierarchical model of statistical correlations covering from structural relationships to physiologic links can also be evidenced. (iii) To enhance pattern recognition performances, we have validated a variable selection algorithm for accurate prediction of unknown individuals belonging to predetermined groups achieved by linear discriminant analysis (LDA). This algorithm synthesizes the whole information contained in the data set by selecting preferentially nonredundant variables. Parameters generating variable subsets are validated by predicted variance efficiency obtained when minimizing error rates calculated by cross-validation methods. (iv) Provided variables are correctly filtered, LDA fairly competes with partial least-squares methods for both classification of individuals and statistical interpretation of metabolic responses obtained in such a physiological disruption context.

Algorithms↗

PubMed2026

Reassessing Instrument Strength in Two-Sample Mendelian Randomization Analysis.

Mendelian randomization (MR) analysis is widely used to estimate causal relationships between risk factors and outcomes of interest. Two-sample MR approaches have gained increasing attention in genetic epidemiology due to the growing availability of Genome-Wide Association Study (GWAS) summary statistics from public databases. A critical step in two-sample MR is the selection of genetic variants as instrumental variables (IVs). Although genome-wide significant variants are typically preferred, the inclusion of variants with weaker association p-values is considered, as they may potentially improve power through an increased instrument number of instruments, while they may introduce weak instrument bias and attenuate effect estimates towards the null. Our simulation results show that even modest levels of pleiotropy substantially increase the variability of causal effect estimates, while the inclusion of weak IVs does not substantially affect the direction and variability of causal effect estimates in most cases. In real data analyses, we used two released versions of FinnGen GWAS summary statistics with different sample sizes as exposure GWASs to assess the influence of weak IVs. Here, the inclusion of IVs with higher exposure-association p-values resulted in weakened estimated effect sizes, particularly when the exposure GWAS sample size was small. These findings suggest that incorporating weak IVs is reasonable when the exposure GWAS sample size is large, but it poses a risk of falsely concluding null associations when the exposure GWAS sample size is small.

Journal Article↗

PubMed1967

The relation between heat produced and phosphorylcreatine split during isometric contraction of frog's muscle.

1. Heat production, tension development and phosphorylcreatine (PC) splitting have been measured simultaneously during isometric contractions of iodoacetate-poisoned frogs' sartorii at 0 degrees C. The muscles were stimulated to produce a series of 30 twitches or a 10 sec tetanus or a 30 sec tetanus.2. Of the several possible methods of calculating PC breakdown the best appears to be the one based on the assumption that PC/(total creatine) was originally the same in the two muscles of a pair.3. The difficulty of expressing PC break-down, heat production etc. in terms of the muscle's size is demonstrated.4. Several artifacts are discussed, including the heat produced by the stimulus and the possible role of reactions other than PC splitting.5. Even when these have been substantially eliminated there remains the rather intractable statistical problem of establishing a functional relationship between heat produced and PC split when both of these variables contain errors, so that ordinary regression analysis is misleading. It is shown that this problem can be dealt with satisfactorily by introducing other instrumental variables that can be determined experimentally.6. The final conclusion is that the in vivo enthalpy of hydrolysis of PC is about 10.6 kcal/mole, and is the same in twitches and in tetani.

Animals↗

PubMed2001

Successful aging.

OBJECTIVE: Until now, prospective studies of aging have begun with 50-60-year-olds, not adolescents. Premature death, childhood variables, and alcohol abuse have been often ignored, as has successful aging. METHOD: The authors reviewed the existing literature on health in late life in order to highlight that, increasingly, successful aging is not an oxymoron. The present study followed two cohorts of adolescent boys (237 college students and 332 core-city youth) for 60 years or until death. Complete physical examinations were obtained every 5 years and psychosocial data every 2 years. Predictor variables assessed before age 50 included six variables reflecting uncontrollable factors: parental social class, family cohesion, major depression, ancestral longevity, childhood temperament, and physical health at age 50 and seven variables reflecting (at least some) personal control: alcohol abuse, smoking, marital stability, exercise, body mass index, coping mechanisms, and education. The six outcome variables chosen to assess successful aging at age 70-80 included four objectively assessed variables (physical health, death and disability before age 80, social supports, and mental health) and two self-rated variables (instrumental activities of daily living and life enjoyment). RESULTS: Multivariate analysis suggested that "good" and "bad" aging from age 70-80 could be predicted by variables assessed before age 50. More hopeful still, if the seven variables under some personal control were controlled, depression was the only uncontrollable predictor variable that affected the quality of subjective and objective aging. CONCLUSIONS: One may have greater personal control over one's biopsychosocial health after retirement than previously recognized.

Adolescent↗

PubMed2004

Endogeneity bias in the absence of unobserved heterogeneity.

PURPOSE: To demonstrate that endogeneity bias can still arise even when no unobserved heterogeneity exists. METHODS: A formal mathematical proof and a Monte Carlo simulation are used to demonstrate that ordinary estimation techniques will generate biased parameter estimates. RESULTS: The Monte Carlo results support the formal proof. Even in the absence of unobserved heterogeneity, ordinary least squares estimation that does not account for the endogenous nature of an explanatory variable resulted in a parameter estimate for the endogenous variable that was significantly biased (by a factor of 1.42 for the simple model and 1.98 for the saturated model). Alternatively, controlling for endogeneity using the instrumental variables approach led to an unbiased parameter estimate. CONCLUSIONS: Endogeneity bias can still occur even when unobserved heterogeneity is not present.

Algorithms↗

PubMed2005

Mortality benefit of transfer to level I versus level II trauma centers for head-injured patients.

OBJECTIVE: To determine whether head-injured patients transferred to level I trauma centers have reduced mortality relative to transfers to level II trauma centers. DATA SOURCE/STUDY SETTING: Retrospective cohort study of 542 patients with head injury who initially presented to 1 of 31 rural trauma centers in Oregon and Washington, and were transferred from the emergency department to 1 of 15 level I or level II trauma centers, between 1991 and 1994. STUDY DESIGN: A bivariate probit, instrumental variables model was used to estimate the effect of transfer to level I versus level II trauma centers on 30-day postdischarge mortality. Independent variables included age, gender, Injury Severity Scale (ISS), other indicators of injury severity, and a dichotomous variable indicating transfer to a level I trauma center. The differential distance between the nearest level I and level II trauma centers was used as an instrument. PRINCIPAL FINDINGS: Patients transferred to level I trauma centers differ in unmeasured ways from patients transferred to level II trauma centers, biasing estimates based on standard statistical methods. Transfer to a level I trauma center reduced absolute mortality risk by 10.1% (95% confidence interval 0.3%, 22.2%) compared with transfer to level II trauma centers. CONCLUSIONS: Patients with severe head injuries transferred from rural trauma centers to level I centers are likely to have improved survival relative to transfer to level II centers.

Catchment Area, Health↗

PubMed1999

Standardization of carotid ultrasound: a hemodynamic method to normalize for interindividual and interequipment variability.

BACKGROUND AND PURPOSE: Accurate carotid Doppler examination is an important issue in the light of large endarterectomy trials, but recommended cutoff values for detection of >70% stenosis vary widely. Standardization of diagnostic criteria should consider patient variation and instrument variability. METHODS: We prospectively analyzed various Doppler parameters in 44 patients undergoing carotid angiography to evaluate whether normalization through individual reference measurements from the common carotid artery or the distal internal carotid artery could improve accuracy. For assessment of interindividual and interequipment variability, we performed repeated measurements of 40 carotid arteries in 21 patients. Two color-coded duplex ultrasound systems were compared for machine variability estimation: Hewlett Packard SONOS 2500 and ATL Ultramark 9 HDI. RESULTS: Intrastenotic divided by distally recorded mean blood flow velocity (mean velocity ratio) showed the closest correlation with angiography: R2=0.93. Mean velocity ratio >5 was 97% sensitive and 98% specific for detection of >70% carotid stenosis. Intrastenotic blood flow velocities were significantly different between the 2 duplex systems (0.22+/-0.16 versus 0.17+/-0. 11 m/s; P<0.001), whereas mean velocity ratio values did not differ significantly. Interobserver variation expressed as 95% CI for predicted stenosis between 2 observers was 13.6% (peak systolic velocity) and 15.4% (mean velocity ratio). CONCLUSIONS: A mean velocity ratio using distal reference measurement in the internal carotid artery can normalize for interindividual and interequipment variability.

Aged↗

PubMed2003

Wage rentals for reproducible human capital: evidence from Ghana and the Ivory Coast.

Education, child nutrition, adult health/nutrition, and labor mobility are critical factors in achieving recent sustained growth in factor productivity. To compare the contribution of these four human capital inputs, an expanded specification of the wage function is estimated from household (LSMS) surveys of the Ivory Coast and Ghana. Specification tests assess whether the human capital inputs are exogenous, and instrumental variable techniques are used to estimate the wage function. Smaller panels from the Ivory Coast imply the magnitude of measurement error in the human capital inputs and provide more efficient instruments to estimate the wage equation. The conclusion emerges that weight-for-height and height are endogenous, particularly prone to measurement error, and heterogeneous in their effects on wages. Overall returns to these four forms of human capital are similar within each country for men and women, but education and migration returns are higher in the more rapidly growing Ivory Coast, and the wage effects of child nutrition proxied by height are greater in poorer, more malnourished Ghana.

Adolescent↗

PubMed2000

Impact of HMO market structure on physician-hospital strategic alliances.

OBJECTIVE: To assess the impact of HMO market structure on the formation of physician-hospital strategic alliances from 1993 through 1995. The two trends, managed care and physician-hospital integration have been prominent in reshaping insurance and provider markets over the past decade. STUDY DESIGN: Pooled cross-sectional data from the InterStudy HMO Census and the Annual Survey conducted by the American Hospital Association (AHA) between 1993 and the end of 1995 to examine the effects of HMO penetration and HMO numbers in a market on the formation of hospital-sponsored alliances with physicians. Because prior research has found nonlinear effects of HMOs on a variety of dependent variables, we operationalized HMO market structure two ways: using a Taylor series expansion and cross-classifying quartile distributions of HMO penetration and numbers into 16 dummy indicators. Alliance formation was operationalized using the presence of any alliance model (IPA, PHO, MSO, and foundation) and the sum of the four models present in the hospital. Because managed care and physician-hospital integration are endogenous (e.g., some hospitals also sponsor HMOs), we used an instrumental variables approach to model the determinants of HMO penetration and HMO numbers. These instruments were then used with other predictors of alliance formation: physician supply characteristics, the extent of hospital competition, hospital-level descriptors, population size and demographic characteristics, and indicators for each year. All equations were estimated at the MSA level using mixed linear models and first-difference models. PRINCIPAL FINDINGS: Contrary to conventional wisdom, alliance formation is shaped by the number of HMOs in the market rather than by HMO penetration. This confirms a growing perception that hospital-sponsored alliances with physicians are contracting vehicles for managed care: the greater the number of HMOs to contract with, the greater the development of alliances. The models also show that alliance formation is low in markets where a small number of HMOs have deeply penetrated the market. First-difference models further show that alliance formation is linked to HMO consolidation (drop in the number of HMOs in a market) and hospital downsizing. Alliance formation is not linked to changes in hospital costs, profitability, or market competition with other hospitals. CONCLUSIONS: Hospitals appear to form alliances with physicians for several reasons. Alliances serve to contract with the growing number of HMOs, to pose a countervailing bargaining force of providers in the face of HMO consolidation, and to accompany hospital downsizing and restructuring efforts. IMPLICATIONS FOR POLICY, DELIVERY, OR PRACTICE: Physician-hospital integration is often mentioned as a provider response to increasing cost-containment pressures due to rising managed care penetration. Our findings do not support this view. Alliances appear to serve the hospital's interest in bargaining with managed care plans on a more even basis.

Delivery of Health Care, Integrated↗

PubMed1998

The effects of measurement error in response variables and tests of association of explanatory variables in change models.

Biomedical studies often measure variables with error. Examples in the literature include investigation of the association between the change in some outcome variable (blood pressure, cholesterol level etc.) and a set of explanatory variables (age, smoking status etc.). Typically, one fits linear regression models to investigate such associations. With the outcome variable measured with error, a problem occurs when we include the baseline value of the outcome variable as a covariate. In such instances, one can find a relationship between the observed change in the outcome and the explanatory variables even when there is no association between these variables and the true change in the outcome variable. We present a simple method of adjusting for a common measurement error bias that tends to be overlooked in the modelling of associations with change. Additional information (for example, replicates, instrumental variables) is needed to estimate the variance of the measurement error to perform this bias correction.

Bias↗

PubMedDate not supplied

Direct assessment of profilometric roughness variability from typical implant surface types.

PURPOSE: Protocols for quantifying the surface roughness of implants are varied and dependent upon the roughness parameter produced by the particular measurement device. The objective of this study was to examine the accuracy and precision of typical roughness characterization instruments used in the dental implant industry. MATERIALS AND METHODS: The average roughness (Ra) was measured using 2 common surface characterization instruments: an interferometer and a stylus profilometer. Titanium disks were prepared to represent 4 typical dental implant surfaces: machined, acid-etched, hydroxyapatite-coated, and titanium plasma-sprayed. Repeated measurements from multiple sites on each surface were undertaken to establish statistical inferences. Qualitative images of the surfaces were also acquired using a laser scanning confocal microscope. After surface measurements were conducted, the disks were diametrically cut and cross-sectional profiles were examined using a scanning electron microscope (SEM) as a comparative measure of surface topography. An analysis of variance was applied to isolate the effects of the measurement site, measurement sequence, surface treatment, and instrument type on Ra values. RESULTS: The results indicated that surface treatment (P = .0001) and instrument (P = .0001) strongly influenced Ra data. By design, measurement site (diametrical: P = .9859; area: P = .9824) and measurement sequence (P = .9990) did not influence roughness. In the assessment of individual instrument accuracy, the interferometer was the most accurate in predicting SEM-based roughness (P = .6688) compared with the stylus (P = .0839). As a measure of aggregate precision over all measurements, the most repeatable instrument was the stylus (coefficient of variation [CV] = 0.108), followed by the interferometer (CV = 0.125) and SEM (CV = 0.273). DISCUSSION: These results indicate dependencies in accuracy and precision related to the surface characterization technique. CONCLUSION: Instrument variability may obscure functional correlations between implant surface topography and osseointegration.

Acid Etching, Dental↗

PubMed1998

Using sensory and instrumental data to interpret the effect of storage at elevated temperatures on aroma of Chardonnay wines.

The effect of elevated temperatures during storage on the aroma of commercial Chardonnay wines was monitored by sensory and instrumental methods. Aromas of wines stored at 40 degrees C for 0, 15, 30 and 45 days were profiled by descriptive analysis by a trained panel. Heated storage decreased intensity of fruity and floral notes, while increasing attributes such as honey, butter/vanilla, oak, and rubber. Volatiles recovered by solvent extraction from the same wines were separated by gas chromatography (GC) and identified by GC-mass spectrometry (MS). Principal component analysis of instrumental variables (PCAIV) was used to reduce the initial set of 67 quantified GC peaks. Six compounds, selected by PCAIV to yield the configuration closest to that of the principal component analysis of the sensory data, provided a highly significant fit with the sensory configuration, as shown by a permutation test. This solution was the statistically optimal one, but was not unique, as demonstrated by significant fits between the sensory and instrumental spaces upon use of other GC peaks, which were highly correlated with the original six variables.

Female↗

PubMed1998

Degenerative spondylolisthesis: when to fuse?

This article reviews four reports that have addressed the efficacy of spinal instrumentation to enhance spinal fusion in patients with degenerative spondylolisthesis. These papers serve to highlight some of the common problems with interpreting and applying the clinical findings of such studies: small, nonuniform patient selection; variable instrumentation techniques; relatively brief follow-up periods (usually less than 5 years); lack of a uniform scale for clinical assessment of patients; and lack of consensus on the definition and clinical documentation of motion segment instability.

Journal Article↗

PubMedDate not supplied

Clinical determinants of long-term mortality in elderly patients with heart disease.

To determine which of the many clinical parameters routinely collected influence mortality in patients with low left ventricular ejection fraction (LVEF) (< 45% at radionuclide ventriculography), 128 elderly patients (mean age 79 +/- 3 years) with various heart diseases were prospectively followed for 3 years. Twenty-eight-percent had coronary heart disease, 16% hypertensive heart disease, 7% valvular heart disease. The remaining 62 patients (48%) made up a group comprising patients with primitive cardiomyopathy, cor pulmonary with no evidence of coronary heart disease, valvular disease or hypertensive heart disease. Thirty-four-percent of all patients were classified as having congestive heart failure (CHF). Age, sex and 37 clinical variables were analyzed using a Cox proportional model. Forty-four patients died, 36 (82%) of sudden cardiac death. Ten characteristics at study entry predicted an increased mortality risk: S3 gallop, number of clinical signs >or= 3, LVEF or= III, dyspnea, digoxin treatment, rales, number of symptoms >or= 4, asthenia, associated pulmonary disease. Long-term survival of very elderly patients with low ejection fraction is related to the functional capacity, the severity of symptoms and the number of clinical signs. Moreover a LVEF <or= 25% selects a subgroup of patients at higher risk. Our results suggest that these variables may influence the long-term survival of elderly patients with heart disease. Further studies with a greater number of patients are necessary to better delineate the prognostic value of the clinical and instrumental variables routinely collected in these patients.

Journal Article↗

PubMed2026

Causality between noise pollution and Alzheimer disease: A Mendelian randomization analysis.

The role of noise pollution as a risk factor for Alzheimer disease (AD) is unclear, with observational studies yielding conflicting results susceptible to confounding and reverse causality. To clarify this relationship, we performed a 2-sample Mendelian randomization (MR) study using summary statistics from large-scale genome-wide association studies of European populations. Genetically predicted daytime and evening noise exposure was used as an instrumental variable to assess a causal effect on AD risk. The primary analysis was conducted using the inverse-variance weighted method, with weighted median and MR-Egger methods as key sensitivity analyses. We assessed instrument validity and pleiotropy using the Cochran Q test, the MR-Egger intercept, and leave-one-out analysis. Our MR analysis found no evidence of a causal association between genetically predicted daytime noise (odds ratio [95% confidence interval] = 0.999 [0.993-1.006], P = .819) or evening noise (odds ratio [95% confidence interval] = 0.999 [0.993-1.005], P = .643) and the risk of AD. Sensitivity analyses were consistent, with no evidence of heterogeneity or directional pleiotropy. In conclusion, this study does not support a direct causal link between noise and AD. While our findings mitigate common observational biases, they do not preclude indirect mechanisms whereby noise may influence AD pathogenesis via established risk pathways, such as chronic sleep disruption and cardiovascular stress. Studies are needed to focus on disentangling these potential indirect effects.

Alzheimer Disease↗

PubMed2006

Differential effects of atypical versus typical antipsychotic medication on earnings of schizophrenia patients : estimates from a prospective naturalistic study.

BACKGROUND: Rising public and private expenditure on antipsychotic medications is concentrated on the cost of second generation or 'atypical' medications, which are more expensive than first generation medications and make up a rapidly growing share of all antipsychotic prescriptions. Previous studies have examined whether the higher acquisition costs of atypicals are offset by other cost and/or utilisation benefits. This paper extends this literature by examining possible effects of atypicals on earnings and related measures of labour supply in a large naturalistic study with a long-term follow-up period. METHODS: We analysed data on earnings and other characteristics from the Schizophrenia Care and Assessment Program (SCAP), a 3-year longitudinal study (with data collection during the years 1997-2003) of 2327 adults with schizophrenia (including schizoaffective and schizophreniform disorders) recruited from behavioural healthcare provider systems in six areas of the US. We used empirical criteria and data from the SCAP database to identify 336 patients aged < 50 years who were in the stable or 'maintenance' phase of their antipsychotic treatment during the 6 months prior to baseline. Effects of atypicals compared with typicals were estimated from Tobit regression models that included additional covariates and the baseline-dependent variable values. Regression-dependent variables were reported earnings per month, hours worked per month, days worked per month and a binary indicator of employment. To control for the effect of selection bias in choice of type of atypical, we employed an instrumental variables (IV) estimation procedure. RESULTS: For all dependent variables, our IV Tobit regressions yielded consistently positive coefficient estimates for atypical use that were either marginally significant (p < 0.1) or significant (p < 0.05) for earnings, significant for hours and days of work and not as consistently significant for employment status. Results from these regressions imply a positive effect of atypical use on monthly earnings in the range of Dollars US 107-122. In regressions that did not control for selection bias by using IVs, coefficients for atypical use were often negative and never statistically significant. CONCLUSIONS: Our results indicate that higher drug costs of atypicals for maintenance-phase treatment are at least partially offset by higher earnings among patients. These effects represent benefits to consumers as well as savings to taxpayer-supported income transfer programmes. Future studies should seek to determine if treatment with atypicals increases patients' earnings via better control over negative symptoms and/or improved patient cognition. Both appear to be connected with employment and labour supply in patients with schizophrenia, and both may be improved through use of atypicals.

Antidepressive Agents, Second-Generation↗

PubMed1996

Instrument effect on the activated protein C resistance plasma assay performed by a commercial kit.

In order to evaluate the influence of the coagulation instrument on the activated protein C (APC)-resistance plasma assay performed by a commercial kit, we tested 70 plasma samples on 4 different instruments during a simultaneous session run using a same lot of Coatest APC-resistance (Chromogenix). The results were analyzed employing three different modes of expression (aPTT prolongation in the presence of APC, APC-sensitivity ratio, normalized APC-sensitivity ratio) and three different diagnostic threshold values (below the control mean--2 standard deviations or the lowest control value or the 5th percentile of the control values). The inter-instruments variability in the mean values of the control individuals can be limited expressing the results as normalized-APC-sensitivity ratio (range 0.99-1.05). The overall diagnostic yield in thrombotic patients and their relatives depended mainly on the instrument employed and only in some cases on the mode of expression of the results and on the diagnostic threshold value. The sensitivity of the commercial assay on heterozygotes for factor V Leiden diagnosed by gene analysis was overall satisfactory (75-100%) but in some cases a lower diagnostic yield was noticed, depending on the type of instrument employed and/or the type of expression of the results and/or the diagnostic threshold values. Thus the instrument system adopted should be carefully considered in the interpretation of the results using the commercial kit.

Blood Coagulation Tests↗