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PubMedDate not supplied

Comparison ot two methods of measurements of the same substance: an evaluation of some statistical procedures.

Linear regression analysis and calculation of the correlation coefficient are usually used to compare the results of two methods of measurement of the same substance. The limitations of these procedures are illustrated with numerical examples, in which X (the independent variable contains random errors of measurement. Formulas are given for estimating a linear functional relationship in this case. An alternative procedure, not involving linear regression, is described in which means and variances of replicate measurements by each method are compared at various concentrations over the analytical range. The appropriate statistical tests are discussed.

Regression Analysis↗
PubMed2005

Assessment of the esophageal pressure in gastroesophageal reflux disease by the local regression.

Gastroesophageal reflux disease (GERD) is one of the most prevalent gastrointestinal diseases. It is characterized by excessive reflux of gastric content (acid, pepsin, etc.) into the esophagus causing symptoms (heartburn, acid regurgitation, etc.) and mucosal inflammation and injuries. GERD occurs when the lower esophageal sphincter (LES) has a low resting pressure and stomach contents leak back, or reflux, into the esophagus. Therefore, the accurate measurement of the LES pressure is of great importance for the diagnosis of GERD. The LES pressure signal, involving severe respiratory contamination and motion artifacts, demands specific capabilities not provided by conventional data analysis methods. Recently, local regression has proved to be a very attractive technique to the nonparametric regression in statistics. In this contribution we apply the ideas of local regression to develop strategies for selecting smoothing parameters of local linear squares estimators, and present its application on the extraction of the LES pressure in GERD. The results from both extensive simulations and real data demonstrate the ability of local regression to characterize the LES pressure, which is consistent with the clinical observation.

Computer Simulation↗
PubMed2005

Association of HLA-DRB3*0202 and serum IgG antibodies to Chlamydia pneumoniae with essential hypertension in a highly homogeneous population from Majorca (Balearic Islands, Spain).

Separate studies investigating the relationship of essential hypertension (EH) with the HLA system and with Chlamydia pneumoniae (C. pneumoniae) infection have given conflicting results. Our aim was to clarify these relationships and determine whether the HLA system and C. pneumoniae infection interact with respect to the risk for EH. An association study (110 essential hypertensives and 107 controls) was conducted in a highly homogeneous population in the Balearic Island of Majorca (Spain). Molecular typing of HLA-B and HLA-DRB and quantification of serum levels of IgG antibodies to C. pneumoniae (sIgGa-Cp) were determined. Student's t-test, chi(2)-statistics, logistic regression analysis, and general linear model ANOVA were used for statistical analysis. The results showed that EH was related with HLA-DRB3*0202 in the whole study population, and with levels of sIgGa-Cp>63.5 BU/ml in the group of individuals with sIgGa-Cp>30 BU/ml (OR (95% CI) adjusted for obesity, familial history of EH and diabetes=2.06 (1.07-3.97), P=0.03, and =4.60 (1.06-19.90), P=0.04, respectively). The association between EH and sIgGa-Cp was observed in the DRB3*0202(+) individuals, but not in the DRB3*0202(-) subgroup (OR (95% CI)=11.14 (1.92-64.54), P=0.004, and =0.98 (0.22-4.43), P=0.64, respectively (P of the Mantel-Haenszel test for homogeneity of OR=0.06)). In our population, EH was positively associated with HLA-DRB3*0202 and with high levels of sIgGa-Cp. Moreover, a significant interaction of DRB3*0202 on the effect of sIgGa-Cp was observed, as the association of EH with these antibodies depended on the presence of DRB*0202.

Adult↗
PubMed1991

Poisson regression with misclassified counts: application to cervical cancer.

"Errors in disease classification can give misleading inferences for covariate effects when the probability of error is itself related to the covariates. More accurate inferences are possible using supplemental data on both true and fallible disease counts at various covariate levels. We present a method for incorporating such supplemental data into disease rate regression and use it to show that, although observed intercountry differences in European cervical cancer mortality rates are exaggerated by errors in death certification, they are not completely explained by such errors." The data concern Belgium, England and Wales, France, and Italy.

Belgium↗
PubMed1989

Methods for estimating cohort replacement effects.

The author reexamines the hypothesis developed by Norman Ryder that the birth and death of individuals constitutes a massive process of personnel replacement that holds enormous potential for social change. "In this paper I describe and illustrate six possible ways to estimate cohort (personnel) replacement effects: three based on algebra (Kitagawa's two-component method, forward partitioning, and backward partitioning), and three based on regression (regression standardization, survey metric analysis, and linear decomposition). Assuming monotonic change, regression methods typically are better, because standard algebraic methods are ill suited for analyzing change with regard to birth cohorts that enter or exit during the period studied."

Cohort Studies↗
PubMed2001

A statistical model to compare road mortality in OECD countries.

The objective of this paper is to compare safety levels and trends in OECD countries from 1980 to 1994 with the help of a statistical model and to launch international discussion and further research about international comparisons. Between 1980 and 1994, the annual number of fatalities decreased drastically in all the selected countries except Japan (+ 12%), Greece (+ 56%) and ex-East Germany (+ 50%). The highest decreases were observed in ex-West Germany (- 48%), Switzerland (- 44%), Australia (- 40%), and UK (- 39%). In France, the decrease in fatalities over the same period reached 34%. The fatality rate, an indicator of risk, decreased in the selected countries from 1980 to 1994 except in the east-European countries during the motorization boom in the late 1980s. As fatality rates are not sufficient for international comparisons, a statistical multiple regression model is set up to compare road safety levels in 21 OECD countries over 15 years. Data were collected from IRTAD (International Road Traffic and Accident Database) and other OECD statistical sources. The number of fatalities is explained by seven exogenous (to road safety) variables. The model, pooling cross-sectional and time series data, supplies estimates of elasticity to the fatalities for each variable: 0.96 for the population; 0.28 for the vehicle fleet per capita; -0.16 for the percentage of buses and coaches in the motorised vehicle fleet; 0.83 for the percentage of youngsters in the population; - 0.41 for the percentage of urban population; 0.39 for alcohol consumption per capita; and 0.39 for the percentage of employed people. The model also supplies a rough estimate of the safety performance of a country: the regression residuals are supposed to contain the effects of essentially endogenous and unobserved variables, independent to the exogenous variables. These endogenous variables are safety performance variables (safety actions, traffic safety policy, network improvements and social acceptance). A new indicator, better than the mortality rate, is then set upon the residuals. Mean estimates of this indicator for the years 1980-1982 and the years 1992-1994 rank the countries in the beginning and at the end of the study period. Countries showing the best ranks (and thus the best performance) in 1980 and 1994 are Sweden, the Netherlands and Norway. The UK and Switzerland reach the top 5 in 1994. Greece, Belgium, Portugal and Spain are the last countries in the classification along with, surprisingly, the USA. France was ranked 18th in 1980 and 15th in 1994 but is ranked amongst the five countries that most improved from 1980 to 1994. This model remains non definitive because it is not able to distinguish between safety performance and unobserved exogenous variables although these exogenous variables could explain more about the differences in levels and trends between the countries. More complex models, particularly highly sophisticated models regarding the number of fatalities with breakdowns by road users or road classes would be needed to give a precise and profound ranking of safety levels and safety improvements between countries.

Accidents, Traffic↗
PubMed2005

Half-a-dozen ribs: the breakpoint for mortality.

BACKGROUND: We hypothesized that the number of rib fractures independently impacted patient pulmonary morbidity and mortality. METHODS: The National Trauma Data Bank (NTDB, v. 3.0 American College of Surgeons, Chicago, IL) was queried for patients sustaining 1 or more rib fractures. Data abstracted included the number of rib fractures by International Classification of Diseases-9 code, Injury Severity Score, the occurrence of pneumonia, acute respiratory distress syndrome, pulmonary embolus, pneumothorax, aspiration pneumonia, empyema, and associated injuries by abbreviated injury score, the need for mechanical ventilation, number of ventilator days, intensive care unit (ICU) length of stay (LOS), hospital LOS, mortality, and use of epidural analgesia. Statistical analysis was performed using the Student t test and linear regression analysis. Statistical significance was defined as a P value of less than .05. RESULTS: The NTDB included 731,823 patients. Of these, 64,750 (9%) had a diagnosis of 1 or more fractured ribs. Thirteen percent (n = 8,473) of those with rib fractures developed 13,086 complications, of which 6,292 (48%) were related to a chest-wall injury. Mechanical ventilation was required in 60% of patients for an average of 13 days. Hospital LOS averaged 7 days and ICU LOS averaged 4 days. The overall mortality rate for patients with rib fractures was 10%. The mortality rate increased (P < .02) for each additional rib fracture. The same pattern was seen for the following morbidities: pneumonia (P < .01), acute respiratory distress syndrome (P < .01), pneumothorax (P < .01), aspiration pneumonia (P < .01), empyema (P < .04), ICU LOS (P < .01), and hospital LOS for up to 7 rib fractures (P < .01). An association between increasing hospital LOS and number of rib fractures was not shown (P = .19). Pulmonary embolism also was not related to the number of rib fractures (P = .06). Epidural analgesia was used in 2.2% (n = 1,295) of patients with rib fractures. A reduction in mortality with epidural analgesia was shown at 2, 4, and 6 through 8 rib fractures. The use of epidural analgesia had no impact on the frequency of pulmonary complications. When stratifying data by Injury Severity Score and the presence or absence of rib fractures the mortality rates were similar. CONCLUSIONS: Increasing the number of rib fractures correlated directly with increasing pulmonary morbidity and mortality. Patients sustaining fractures of 6 or more ribs are at significant risk for death from causes unrelated to the rib fractures. Epidural analgesia was associated with a reduction in mortality for all patients sustaining rib fractures, particularly those with more than 4 fractures, but this modality of treatment appears to be underused.

Anesthesia, Epidural↗
PubMed2006

Randomized trial of an intervention to improve mammography utilization among a triracial rural population of women.

INTRODUCTION: Mammography is underused by certain groups of women, in particular poor and minority women. We developed a lay health advisor (LHA) intervention based on behavioral theories and tested whether it improved mammography attendance in Robeson County, NC, a rural, low-income, triracial (white, Native American, African American) population. METHODS: A total of 851 women who had not had a mammogram within the past year were randomly assigned to the LHA intervention (n = 433) or to a comparison arm (n = 418) during 1998-2002. Rates of mammography use after 12-14 months (as verified by medical record review) were compared using a chi-square test. Baseline and follow-up (at 12-14 months) surveys were used to obtain information on demographics, risk factors, and barriers, beliefs, and knowledge about mammography. Linear regression, Mantel-Haenszel statistics, and logistic regression were used to compare barriers, beliefs, and knowledge from baseline to follow-up and to identify baseline factors associated with mammography. RESULTS: At follow-up, 42.5% of the women in the LHA group and 27.3% of those in the comparison group had had a mammogram in the previous 12 months (relative risk = 1.56, 95% confidence interval [CI] = 1.29 to 1.87). Compared with those in the comparison group, women in the LHA group displayed statistically significantly better belief scores (difference = 0.46 points on a 0-10 scale, 95% CI = 0.15 to 0.77) and reduced barriers at follow-up (difference = -0.77 points, 95% CI = -1.02 to -0.53), after adjusting for baseline scores. CONCLUSIONS: LHA interventions can improve mammography utilization. Future studies are needed to assess strategies to disseminate effective LHA interventions to underserved populations.

Adult↗
PubMed2003

Linear displacement and force induced by polymerization shrinkage of resin-based restorative materials.

PURPOSE: To measure the linear displacement and force induced by polymerization shrinkage of a series of resin-based restorative materials. METHODS: The materials tested were 10 ultrafine midway-filled resin-based composites, mainly used in anterior restorations (Brilliant Dentin, Brilliant Enamel, Charisma F, Pertac II Aplitip, Prodigy, Resulcin, Sculpt-it, Synergy Duo, Tetric and Z100), 11 ultrafine compact-filled composites, suggested by the manufacturers as "amalgam substitutes" for posterior restorations (Alert, Ariston pHc, Definite, EXI-119, EXI-120, Nulite F, Prodigy Condensed, Prodigy High Viscosity, Solotaire, Surefil and Synergy Compact), and six polyacid-modified composites (Compoglass, Dyract, Dyract AP, Elan, F2000 and Hytac Aplitip), also known as compomers. Each property was measured for 180 seconds from the start of curing with the help of custom made devices in eight specimens for each material. Statistical evaluation of the data was performed with one-way ANOVA, Tukey's Studentized Range (HSD) Test (P= 0.05) and simple linear regression. RESULTS: Statistically significant differences among groups and among composites were found for both of the properties that were studied. The ultrafine compact-filled composites (amalgam substitutes) exhibited the least linear displacement, followed by the polyacid-modified composites (compomers) and the ultrafine midway-filled composites, with statistically significant differences among all groups. The groups followed the same order in the polymerization force, with only the compomer-amalgam substitute comparison not being statistically significantly different. The simple linear regression showed that the two studied properties were also highly correlated (r=0.89).

Analysis of Variance↗
PubMed1977

Halothane solubility in human blood.

In a study of the influence of nutritional state on halothane anaesthesia, results were obtained which showed how the blood/gas partition coefficient for halothane varied with blood chemistry in 20 patients undergoing elective surgery. For each patient the partition coefficient lambda was measured by equilibration at 37 degrees C of a blood sample with a 1% halothane in 5% carbon dioxide in air mixture, followed by chemical extraction and estimation of the halothane content by gas chromatography. The haematocrit and haemoglobin, serum albumin, total protein, triglyceride and cholesterol concentrations were measured by routine laboratory methods. Regressions were sought of lambda on each of these, and on the globulin concentration and the ratios of albumin: globulin and albumin: total protein, deduced from these determinations. The only statistically significant regression (P = 0.0004) was that of lambda on the serum triglyceride concentration (T) (mmol/litre): lambda = 1.83 + 0.424T. The dependence of lambda on haemoglobin concentration was not statistically significant, but the slope of the regression was consistent with those of previous investigators. The regressions of lambda, corrected to the mean triglyceride concentration, on the ratios of albumin: globulin and albumin: total protein were not statistically significant but were not significantly different from an earlier reported result.

Anesthesia, Inhalation↗