Birth control and low-income Mexican-American women: the impact of three values.
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Acculturation↗
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Results for “Statistical Regression”
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Prediction from an integrated regression equation: a forestry application.
Models to depict the tapering of a tree bole abound in the literature of forest science, and such models are widely used in forestry practice. One important use is the integration of a taper equation to predict the volume of the tree bole. The statistical properties of volume prediction from an integrated taper equation have been obscure. Based on the statistical characteristics of a taper model for the bole's cross-sectional area, we derive the first two moments of the volume predictor and the prediction error. Bias from the integration is nil. The importance of a reasonable model of the error structure is demonstrated.
Biometry↗
A prospective, randomized study of the chorionic gonadotropin-time relationship in early gestation: clinical implications.
OBJECTIVE: To investigate the hCG-time relationship in early pregnancy. DESIGN: Prospective, randomized study. SETTING: Pregnant human volunteers in a university-based clinical research environment. PATIENTS: Normal pregnant women with viable singleton pregnancies, conceived spontaneously or after ovulation induction. INTERVENTIONS: Vaginal ultrasound was performed, and blood samples were obtained for hormone parameters between 20 and 30 days after conception. The timing of the tests was determined by random assignment using sealed envelopes. MAIN OUTCOME MEASURE: Serum hCG. RESULTS: The log hCG-time relationship was linear, both during the first 20 days and between 20 and 30 days after conception. The inclusion of a quadratic term in either regression was not statistically significant. The slopes of the two regression lines were also not statistically different. CONCLUSION: For practical purposes, the hCG-time relationship in early pregnancy can be treated as log-linear, but short sampling intervals should be used if doubling times are to be calculated from paired samples.
Chorionic Gonadotropin↗
Corneal and refractive error astigmatism in Singaporean schoolchildren: a vector-based Javal's rule.
BACKGROUND: Traditional approaches to Javal's rule do not use data from subjects with oblique astigmatism and have not been used to make predictions about subjects with oblique astigmatism. Vector approaches to analyzing refractive error can circumvent these problems. METHODS: Subjects were 993 Singaporean schoolchildren. We performed linear regression of refractive error astigmatism on corneal astigmatism, using J0 vectors to describe with-the-rule and against-the-rule astigmatism and J45 vectors to describe oblique astigmatism. RESULTS: We obtained the following statistically significant regression relationships: RJ0 = 0.931 x CJ0 - 0.276 and RJ45 = 0.638 x CJ45 + 0.010, where R and C denote refractive error astigmatism and corneal astigmatism, respectively. CONCLUSION: Our vector-based Javal's rule gives closer predictions of refractive astigmatism than the original Javal's rule and the simplified Javal's rule and can be applied in cases of corneal oblique astigmatism.
Adolescent↗
Increased risk of death from measles in children with a sibling of opposite sex in Senegal.
OBJECTIVE: To examine whether contracting measles from a sibling of the opposite sex affects mortality. DESIGN: Prospective registration during 15-20 years of all births and deaths, including 243 measles related deaths. Measles infection was not registered; however, as in fatal cases measles was probably contracted from a maternal sibling the risk of dying during measles outbreaks was examined in families with two boys, two girls, or a boy and a girl. SETTING: 31 small villages in two rural areas of eastern Senegal. SUBJECTS: 766 children living in families with two children aged under 10 years during outbreaks of measles, 107 (14%) of whom died of measles. MAIN OUTCOME MEASURE: Deaths from measles, size of village, age and sex of maternal siblings. RESULTS: The interval between outbreaks in the same village was greater than 10 years. The risk of dying of measles was significantly related to age, increasing with the age difference between siblings and decreasing with the size of village. In a multiple logistic regression analysis adjusting for these background factors, children in families with a boy and a girl had a significantly higher mortality than children in families with two boys or two girls (odds ratio = 1.81, 95% confidence interval 1.17 to 2.82). The increase in risk was the same for boys and girls in families with two children one of whom was a boy and one a girl. CONCLUSION: Cross sexual transmission may be an important determinant of severity of measles infection.
Age Factors↗
Rationale for using multiple regression analysis with complex interferences.
Non-specificities and interferences may become complex when they involve the analyte as well as other interfering substances. These non-specificities and interferences are known as analyte-dependent and multi-interferent interferences. Multiple regression analysis has proven valuable in analysing this type of interference, but the theoretical foundation for using multiple regression analysis to study the basic mechanisms of interference has not been explicitly demonstrated. Graph theory can depict and model the basic mechanisms of interferences and the possible interactions. The relationship between the analyte, the interferents, and the response of the instrument to these entities can be approximated by a polymial of order three, which includes partial derivatives and cross-terms. The partial derivatives relate to the different interactions found with the graph theory model. Further, the partial derivatives can be associated with the coefficients in the multiple regression analysis when the respective values of the three variables (analyte, interferent one, and interferent two) are multiplied by one another. One can decide to retain or discard the coefficient of a variable, based on the statistical significance of the coefficient. The respective interactions in the graphic model can then be assembled and the framework of the interference mechanism established.
Bilirubin↗
[A study on the relationship between the level of mortality and health care resources in Korea].
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Asia↗
Post blocking gone too far! Recovery of information and spatial analysis in field experiments.
Federer (1998, Biometrics 54, 471-481) presents two analyses of field data in which high-order polynomials are fitted as random regressions to remove spatial variation. We challenge the justification of this approach and suggest some alternatives.
Animals↗
Risk factors for wasting and stunting among children in Metro Cebu, Philippines.
Risk factors for wasting and stunting were examined in a longitudinal study of 18 544 children younger than 30 mo in Metro Cebu, Philippines. Measures of household demographic and socioeconomic characteristics, maternal characteristics and behavior, and child biological variables were analyzed cross-sectionally in six child age-residence strata by using logistic regression. Our results support biological and epidemiologic evidence that wasting and stunting represent different processes of malnutrition. They also indicate that the principal risk factors for stunting and wasting in infants < 6 mo of age were either maternal behaviors or child biological characteristics under maternal control, eg, breast-feeding status and birth weight. After 6 mo of age, household socioeconomic characteristics emerged with behavioral and biological variables as important determinants of malnutrition, eg, father's education and presence of a television and/or radio. Household socioeconomic status influenced the risk of stunting earlier in rural than in urban barangays. Implications of the results for interventions are discussed.
Aging↗
The detection of artefacts in EEG series.
In a clinical trial of an anticonvulsant drug, series of electroencephalogram readings are sometimes obtained. These may contain artefacts, that is patches of atypical values which must be identified and either removed or compensated for before a full analysis can be carried out. Methods for identifying such artefacts are discussed. These include non-parametric methods and also parametric ones combining the ideas of autoregressive modelling and of influence in regression. These methods are described and illustrated on typical data sets.
Artifacts↗
Atypical glandular cells of undetermined significance. Cytologic predictive value for glandular involvement in high grade squamous intraepithelial lesions.
OBJECTIVE: To verify the cytologic predictive value of a diagnosis of atypical glandular cells of undetermined significance (AGUS) in high grade squamous intraepithelial lesions (HSIL) cases. STUDY DESIGN: In a retrospective study, 98 cases of HSIL were reviewed. All patients were referred for colposcopy and directed biopsy to confirm the cytologic diagnoses. Loop excision of the transformation zone was performed to treat clinical lesions. Sensitivity, specificity, positive and negative predictive value were evaluated. Kappa statistics and logistic regression analysis were used to evaluate the findings statistically. RESULTS: By logistic regression analysis, we found that the chance of finding squamous intraepithelial lesions involving glands in AGUS smears was 5.32 times higher than in those with no AGUS. It was 5.74 times higher in cervical intraepithelial neoplasia (CIN) 3 lesions than in CIN 2. CONCLUSION: The cytologic predictive value for HSIL involving glands is statistically significant when specific and objective criteria are used for the AGUS diagnosis.
Adenocarcinoma↗
Regression models for time to seroconversion following experimental bovine leukaemia virus infection.
This paper develops a parametric model for time to seroconversion after experimental bovine leukaemia virus (BLV) infection, and examines the effects of inoculation route, volume of inoculum, type of inoculation material, and antigen status of donor on seroconversion time. We used parametric and nonparametric statistical methodology to analyse interval data on 150 animals from 13 published reports. The log-logistic model fitted the observed times to seroconversion better than the log-normal or Weibull models, which were the considered alternatives.
Animals↗
TSS concentration in sewers estimated from turbidity measurements by means of linear regression accounting for uncertainties in both variables.
In order to replace traditional sampling and analysis techniques, turbidimeters can be used to estimate TSS concentration in sewers, by means of sensor and site specific empirical equations established by linear regression of on-site turbidity Tvalues with TSS concentrations C measured in corresponding samples. As the ordinary least-squares method is not able to account for measurement uncertainties in both T and C variables, an appropriate regression method is used to solve this difficulty and to evaluate correctly the uncertainty in TSS concentrations estimated from measured turbidity. The regression method is described, including detailed calculations of variances and covariance in the regression parameters. An example of application is given for a calibrated turbidimeter used in a combined sewer system, with data collected during three dry weather days. In order to show how the established regression could be used, an independent 24 hours long dry weather turbidity data series recorded at 2 min time interval is used, transformed into estimated TSS concentrations, and compared to TSS concentrations measured in samples. The comparison appears as satisfactory and suggests that turbidity measurements could replace traditional samples. Further developments, including wet weather periods and other types of sensors, are suggested.
Calibration↗
Fetal lung volumetry using two- and three-dimensional ultrasound.
OBJECTIVES: To compare methods of measuring fetal pulmonary volume and to establish nomograms of fetal pulmonary volume according to gestational age for the accurate diagnosis of pulmonary hypoplasia. METHODS: Three methods of measuring fetal pulmonary volume in 39 normal fetuses were compared: two-dimensional (2D) ultrasound measurement assuming that the lung is a geometrical pyramid, three-dimensional (3D) ultrasound using the VOCAL rotational method, and the conventional multiplanar 3D mode. Linear regression was used to construct an equation for 3D volume calculation from 2D measurements (the re-evaluated pulmonary volume equation (RPVE)). Lung volume measurements were recorded from 622 singleton fetuses in order to construct nomograms. RESULTS: There was no statistically significant difference between the lung volume values obtained using the two 3D modes. However, in comparison with the 2D measurements the volumes obtained were larger (mean difference = 11.99, P < 0.1 x 10(-6)). The relationship between the 2D and 3D volumes was determined using a statistical linear regression method: RPVE (mL) = 4.24 + (1.53 x 2DGPV), where 2DGPV (2D geometric pulmonary volume) = (surface area right lung base (cm2) + surface area left lung base (cm2)) x 1/3 height right lung (cm). Two nomograms were constructed, one for use with 2D and one for 3D technology. CONCLUSION: 2D pulmonary volume assessment can be used in clinical situations where fetal prognosis depends on lung volume and its growth potential. It is routinely available and easy to perform particularly when repeat measurements are required in evaluation of lung growth. We therefore propose this method as an alternative to magnetic resonance imaging or 3D ultrasound.
Adolescent↗
Socioeconomic equity and fertility in developing countries: a block-recursive model.
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Demography↗
Cervical cancer chemoprevention, vaccines, and surrogate endpoint biomarkers.
At the Second International Conference on Cervical Cancer, held April 11-14, 2002, experts in cervical cancer prevention, detection, and treatment reviewed the need for more research in chemoprevention, including prophylactic and therapeutic vaccines, immunomodulators, peptides, and surrogate endpoint biomarkers. Investigators and clinicians noted the need for more rigorous Phase I randomized clinical trials, more attention to the risk factors that can affect study results in this patient population, and validation of optical technologies that will provide valuable quantitative information in real time regarding disease regression and progression. They discussed the role of the human papillomavirus (HPV) in cervical cancer development and the importance of developing strategies to suppress HPV persistence and progression. Results in Phase I randomized clinical trials have been disappointing because few have demonstrated statistically significant regression attributable to the agent tested. Researchers recommended using a transgenic mouse model to test and validate new compounds, initiating vaccine and immunomodulator trials, and developing immunologic surrogate endpoint biomarkers.
Biomarkers, Tumor↗
Regression models for mixed discrete and continuous responses with potentially missing values.
In this paper a likelihood-based method for analyzing mixed discrete and continuous regression models is proposed. We focus on marginal regression models, that is, models in which the marginal expectation of the response vector is related to covariates by known link functions. The proposed model is based on an extension of the general location model of Olkin and Tate (1961, Annals of Mathematical Statistics 32, 448-465), and can accommodate missing responses. When there are no missing data, our particular choice of parameterization yields maximum likelihood estimates of the marginal mean parameters that are robust to misspecification of the association between the responses. This robustness property does not, in general, hold for the case of incomplete data. There are a number of potential benefits of a multivariate approach over separate analyses of the distinct responses. First, a multivariate analysis can exploit the correlation structure of the response vector to address intrinsically multivariate questions. Second, multivariate test statistics allow for control over the inflation of the type I error that results when separate analyses of the distinct responses are performed without accounting for multiple comparisons. Third, it is generally possible to obtain more precise parameter estimates by accounting for the association between the responses. Finally, separate analyses of the distinct responses may be difficult to interpret when there is nonresponse because different sets of individuals contribute to each analysis. Furthermore, separate analyses can introduce bias when the missing responses are missing at random (MAR). A multivariate analysis can circumvent both of these problems. The proposed methods are applied to two biomedical datasets.
Air Pollution↗
Five-year blood pressure trends and regression-to-the-mean in an industrial population.
OBJECTIVE: To determine trends in blood pressure (BP) and assess the statistical phenomenon of regression to the mean we performed sequential examinations in an industrial population. METHODS: All the employees in an industrial plant were examined. Height, weight, body mass index (BMI) and blood pressure were measured using standardised techniques successively for 5 years as part of annual medical check-up of these employees. All the male employees (n=145) were targeted in the first year of which 122 (84.1%) were examined. These numbers declined to 121, 99, 90 and 87 in subsequent years respectively due to employee attrition. Trends in levels of systolic and diastolic BP and hypertension prevalence were examined using standard regression analysis, least-squares regression and graphic analyses using a commercially available statistical programme. RESULTS: The mean age 31.3 +/- 5.9 years (range 23-41). The mean height was 1.68 + 0.06 m, weight 60.0 + 9.1 kg and BMI 21.2 +/- 3.1 kg/m2. 18 subjects (14.8%) were overweight. From the first to the fifth year, respectively, BMI increased from 21.2 +/- 3.1 kg/m2 to 21.3 +/- 3.9, 21.9 +/- 3.0, 22.3 +/- 3.0 and 22.6 +/- 2.9 kg/m2 (r = 0.93, p = 0.011), systolic BP declined from 127.1 +/- 13.5 to 125.7 +/- 15.4, 125.5 +/- 12.9, 125.0 +/- 12.6 and 124.9 +/- 14.0 mm Hg (r = -0.60, p = 0.034) while diastolic BP remained unchanged (r = 0.15). Prevalence of hypertension (> or =140 / > or =90) declined from 34.4% at baseline to 28.9, 28.3, 24.4 and 24.1% respectively (r = -0.948, p = 0.021). CONCLUSIONS: A high prevalence of hypertension in observed in this young industrial cohort. Without treatment, the hypertension prevalence as well as mean systolic BP decline over time demonstrating the statistical phenomenon of regression to the mean.
Adult↗