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At least 415 records · Page 23Linked to original sources
PubMed2001

How to show that unicorn milk is a chronobiotic: the regression-to-the-mean statistical artifact.

Few chronobiologists may be aware of the regression-to-the-mean (RTM) statistical artifact, even though it may have far-reaching influences on chronobiological data. With the aid of simulated measurements of the circadian rhythm phase of body temperature and a completely bogus stimulus (unicorn milk), we explain what RTM is and provide examples relevant to chronobiology. We show how RTM may lead to erroneous conclusions regarding individual differences in phase responses to rhythm disturbances and how it may appear as though unicorn milk has phase-shifting effects and can successfully treat some circadian rhythm disorders. Guidelines are provided to ensure RTM effects are minimized in chronobiological investigations.

Biometry↗
PubMed1983

Climatic conditions and migration: an econometric inquiry.

"This paper has examined the impact of climate on migration. It has compared the results that are obtained when various indicators of climatic conditions, both those which have been used in the literature and those which have not, are included in a regression used to explain migration behavior. The results suggest that individuals do indeed consider climatic conditions in different areas when deciding where to live; people generally prefer areas which have moderate climates to areas which have either extremely hot or extremely cold climates. The results also indicate that the climate variables which yield the best results are generally those which have not been used in the literature." The study is based on U.S. data concerning in-migration to 36 SMSAs between 1960 and 1970.

Americas↗
PubMed1981

Regression of area mortality rates on explanatory variables: what weighting is appropriate?

"One can often gain insight into the aetiology of a disease by relating mortality rates in different areas to explanatory variables. Multiple regression techniques are usually employed, but unweighted least squares may be inappropriate if the areas vary in population size. Also, a fully weighted regression, with weights inversely proportional to binomial sampling variances, is usually too extreme. This paper proposes an intermediate solution via maximum likelihood which takes account of three sources of variation in death rates: sampling error, explanatory variables and unexplained differences between areas. The method is also adapted for logit (death rates), standardized mortality ratios (SMRs) and log (SMRs). Two [United Kingdom] examples are presented."

Demography↗
PubMedDate not supplied

Population concentration: a consideration of density measures and correlates.

"The purpose of the paper is to explore the nature of association of certain external and internal density measures with each other and with a set of selected variables in four states of India. Pearson's Simple Coefficient of Correlations and Stepwise Multiple Regression were used for analysis of data. The results reinforce the notion of a clear distinction between external and internal density measures and their associative factors in India; the two measures of internal density, although highly correlated, were found to have varied relevance to the dependent variables."

Asia↗
PubMed1981

A framework for estimating causes of death in Indonesia [causes of death in Indonesia].

A number of demographic techniques for the indirect estimation of trends in causes of death in Indonesia are proposed. These involve "the use of rates and proportions derived from other nations experiencing similar levels of mortality to that prevailing in Indonesia. Four sets of estimates were produced, the first based on a regression developed by Preston, the other three derived from national patterns of Mexico, the Philippines, and a composite group of countries. These were compared with available epidemiologic and clinical data from Indonesia to produce a final set of estimates which accord both with known Indonesian patterns and medical findings from other nations."

Asia↗
PubMed1994

A robust goodness-of-fit test statistic with application to ordinal regression models.

We propose a goodness-of-fit test statistic for linear regression with heterogeneous variance, which is asymptotically chi-square if the given model is correct. The test statistic is computed as a quadratic form of observed minus predicted responses. We apply the method to a linear regression for an ordinal categorical response, the wheezing status of a child (no wheeze, wheeze with cold, wheeze apart from cold) as a function of maternal smoking and city of residence.

Child↗
PubMedDate not supplied

Prognostic factors for hypotensive effects of isopropyl unoprostone in eyes with primary open-angle glaucoma.

It has been reported that isopropyl unoprostone, a prostaglandin-related compound, has potent effects in lowering intraocular pressure and that its hypotensive effect is an increase of uveoscleral outflow. In the present study, we investigated the clinical characteristics of the hypotensive effects of this novel antiglaucoma drug in 115 primary open-angle glaucoma (POAG) eyes. The mean intraocular pressure (+/- standard deviation) before the addition of isopropyl unoprostone to the current regimens was 21.3 +/- 4.4 mmHg. The values at 1 month, 3 months, and 6 months after treatment were, respectively, 20.2 +/- 3.9 mmHg, 19.4 +/- 3.4 mmHg, and 18.4 +/- 2.5 mmHg. In POAG, the outflow pressure difference (delta OP), which is determined as (pretreatment pressure - posttreatment pressure)/(pretreatment pressure - 10) x 100 (%), was reduced by more than 20% in 36 (31%) of 115 eyes, 35 (36%) of 97 eyes, and 33 (53%) of 62 eyes, respectively at 1, 3, and 6 months. We defined the "early success" group as eyes with a significant reduction in delta OP (> or = 20%) at 1-month posttreatment. To identify the prognostic factors related to the significant reduction in intraocular pressure occurring after the administration of this drug, we carried out a statistical analysis by logistic regression analysis. Statistical analysis revealed significant prognostic factors: history of cataract surgery (P = 0.0084) and pretreatment pressure levels (P = 0.0105) at 1-month posttreatment. Also, further statistical analysis showed a significant influence of pretreatment pressure levels (P = 0.0010) at 3 months posttreatment. Our study shows an interindividual difference in the responsiveness of hypotensive effects on POAG eyes and some prognostic factors (history of cataract surgery and pretreatment pressure levels) prior to the use of this drug.

Adult↗
PubMed2000

Goodness-of-fit statistics for age-specific reference intervals.

The age-specific reference interval is a commonly used screening tool in medicine. It involves estimation of extreme quantile curves (such as the 5th and 95th centiles) of a reference distribution of clinically normal individuals. It is crucial that models used to estimate such intervals fit the data extremely well. However, few procedures to assess goodness-of-fit have been proposed in the literature, and even fewer have been evaluated systematically. Here we consider procedures based on the distribution of the Z-scores (standardized residuals) from a model and on Pearson chi(2) statistics for observed and expected counts in groups defined by age and the estimated reference centile curves. Two of the procedures (Q and grid tests) are mainly inferential, whereas the third (permutation bands and B-tests) is essentially graphical. We obtain approximations to the null distributions of several relevant test statistics and examine their size and power for a range of models based on real data sets. We recommend Q-tests in all situations where Z-scores are available since they are general, simple to calculate and usually have the highest power among the three classes of test considered. For the cases considered the grid tests are always inferior to the Q- and B- tests.

Age Factors↗
PubMed1990

Measuring importance.

Explore the source record for details and available documents.

Data Interpretation, Statistical↗
PubMedDate not supplied

QSAR analysis of hypoglycemic agents using the topological indices.

The molecular topology model and discriminant analysis have been applied to the prediction of some pharmacological properties of hypoglycemic drugs using multiple regression equations with their statistical parameters. Regression analysis showed that the molecular topology model predicts these properties. The corresponding stability (cross-validation) studies performed on the selected prediction models confirmed the goodness of the fits. The method used for hypoglycemic activity selection was a linear discriminant analysis (LDA). We make use of the pharmacological distribution diagrams (PDDs) as a visualizing technique for the identification and selection of new hypoglycemic agents, and we tested on rats the predictive ability of the model.

Animals↗
PubMed2000

Discrimination and molecular design of new theoretical hypolipaemic agents using the molecular connectivity functions

The molecular topology model and discriminant analysis have been applied to the prediction and QSAR interpretation of some pharmacological properties of hypolipaemic drugs using multivariable regression equations with their statistical parameters. Regression analysis showed that the molecular topology model predicts these properties. The corresponding stability (cross-validation) studies done on the selected prediction models confirmed the goodness of the fits. The method used for hypolipaemic activity selection was a linear discriminant analysis (LDA). We make use of the pharmacological distribution diagrams (PDDs) as a visualizing technique for the identification and design of new hypolipaemic agents.

Journal Article↗