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PubMed1996

A practical procedure for the determination of association constants of the analyte-chiral selector equilibria by capillary zone electrophoresis.

A practical procedure is proposed for the determination of association constants and mobility of the associate of a solute with a chiral selector in chiral separations by capillary zone electrophoresis. The procedure is based on the measurement of the effective mobility of a solute at zero and two different nonzero concentrations of the chiral selector. Simple explicit formulas have been derived in order to calculate the required data. The essence of the procedure is that all mobility data are adjusted to the background electrolyte (BGE) without chiral selector, serving as the viscosity reference. A simple procedure is described for measuring the viscosity of the operational electrolytes directly with the commercial capillary electrophoresis instrumentation, and Walden's rule has been utilized for adjusting the experimental mobility data to constant reference viscosity. The use of the procedure is exemplified by a separation of D,L-tryptophan in BGE containing alpha-cyclodextrin as chiral selector.

Cyclodextrins↗
PubMed2002

Spatio-temporal patterns of neuronal activity: analysis of optical imaging data using geometric shape matching.

Optical imaging of neuronal network activity yields information of spatial dynamics which generally is analyzed visually. The transient appearance of spatial activity patterns is difficult to gauge in a quantifiable manner, or may even altogether escape detection. Here, we employ geometric shape matching using Fréchet distances or straight skeletons to search for pre-selected patterns in optical imaging data with adjustable degrees of tolerance. Data were sampled from fluorescence changes of a voltage-sensitive dye recorded with a 464-photodiode array. Fluorescence was monitored in a neuronal network in vitro. Neuronal activity prompting fluorescence fluctuations consisted of spontaneous epileptiform discharges in neocortical slices from patients undergoing epilepsy surgery. The experiments show that: (a) spatial activity patterns can be detected in optical imaging data; (b) shapes such as "mini-foci" appear in close correlation to bioelectric discharges monitored with field potential electrodes in a reproducible manner; (c) Fréchet distances yield more conservative matches regarding rectangular, and less conservative hits with respect to radially symmetric shapes than the straight skeleton approach; and (d) tolerances of 0.03-0.1 are suited to detect faithful images of pre-selected shapes, whereas values >0.8 will report matches with any polygonal pattern. In conclusion, the methods reported here are suited to detect and analyze spatial, geometric dynamics in optical imaging data.

Algorithms↗
PubMed1993

Combining census, dual-system, and evaluation study data to estimate population shares.

"The 1990 [U.S.] census and Post-Enumeration Survey produced census and dual system estimates (DSE) of population by domain, together with an estimated sampling covariance matrix of the DSE. Estimates of the bias of the DSE were derived from various PES evaluation programs. Of the three sources, the unadjusted census is the least variable but is believed to be the most biased, the DSE is less biased but more variable, and the bias estimates may be regarded as unbiased but are the most variable. This article addresses methods for combining the census, the DSE, and bias estimates obtained from the evaluation programs to produce accurate estimates of population shares, as measured by weighted squared- or absolute-error loss functions applied to estimated population shares of domains."

Americas↗
PubMed1994

Comparison of litter adjustment factors in Yorkshire and Landrace data.

National Swine Improvement Federation (NSIF) adjustment factors presently used to standardize litter data for age at 21 d, number born alive (NBA), 21-d litter weight, and number after transfer (NAT) were evaluated using 104,884 litters in 1,348 Yorkshire herds and 20,370 litters in 197 Landrace herds. In addition, adjustment factors for number weaned were calculated for standardization of this trait. Number weaned is adjusted for parity and NAT. The mixed-model least squares, maximum likelihood computer program described by Harvey was used in the analyses. Yorkshire and Landrace data were combined to test for breed effects and interactions involving breed. Breed interactions were different (P < .05). Therefore, breed-specific adjustment factors were calculated for Yorkshire and Landrace data sets. Also, adjustment factors were calculated for combined data that might be appropriate to use for breeds without specific adjustments available. Parity adjustment factors for NBA and 21-d litter weight were different (P < .05) from current NSIF recommendations, as was the NAT adjustment for 21-d litter weight. The age-at-weaning multiplicative factors were not different (P > .05) from current NSIF values. However, in all three data sets, the intercepts and linear coefficients of the quadratic regression for age at weaning were different (P < .05) from NSIF's. A Student-Newman-Keuls (SNK) test was used to evaluate the NSIF groupings of parity and number after transfer.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1998

Analysis, assessment, and presentation of risk-adjusted statewide obstetrical care data: the StORQS II study in Washington State. Statewide Obstetrics Review and Quality System.

OBJECTIVE: To develop an effective, concise presentation of hospital-specific birth event and delivery-related complication rates, including significant deviations from expected rates calculated using risk-adjusted peer hospital data, for distribution to all Washington State hospitals with delivery services. DATA SOURCES: Complete data for calendar year 1993, including inpatient discharge records for mothers and newborns, birth certificates, and infant death records, for 74 hospitals from Washington state source files. STUDY DESIGN: Institutions were classified into four peer groups based on presence of neonatal intensive care units, number of births, and rural/urban location. Twenty-three clinical indicators of procedure (e.g., cesarean section) and complication rates were analyzed and presented. METHODS: For each indicator, observed and expected rates (adjusted within peer group for categorized baseline risk factors) were calculated and presented by institution. Effective graphic and numeric techniques for presenting significant deviations from expected rates were developed. Results were calculated in terms of numbers of events as well as rates. Approaches applicable to institutions with small numbers of deliveries were selected. PRINCIPAL FINDINGS: Exact confidence intervals (C.I.s) for event rates were superior to binomial or Poisson approximations for small hospitals. For calculating expected rates, indirect adjustment was used due to small numbers within risk factor categories. For all indicators, observed and expected rates along with 95 percent C.I.s for the true rate were presented graphically by institution for each peer group. Transforming C.I.s into "statistically acceptable ranges" allowed hospital personnel to assess their performance in terms of actual numbers of events as well as rates. CONCLUSIONS: Readily available statistical methods and straightforward descriptive approaches allow accurate presentation of outcomes for both large and small institutions.

Adult↗
PubMed1985

Adjustment of blood pressure data by season.

Seasonal variation in blood pressure was examined in 801 males of age 50 years and over. Systolic and diastolic pressures revealed significant seasonal patterns with peaks in spring and late autumn and troughs in mid-winter and summer. The blood pressure data standardized for age and body weight (kg/m2) and adjusted for irregular fluctuations showed that the range of variation in systolic pressure within a year was 8-9 mmHg and that in diastolic pressure 5 mmHg. Careful analysis of the data indicates that the variations in blood pressure attributable to the month of the year are at least as significant as those due to age and body weight. An example is drawn from an actual study which demonstrates how estimates of the prevalence of hypertension may be substantially biased if the seasonal pattern in blood pressure is not taken into account. It is therefore suggested that this factor should be allowed for routinely, at least in local epidemiological surveys, in addition it should be recognised as important in daily clinical work--especially in those patients who are in need of antihypertensive treatment.

Age Factors↗
PubMedDate not supplied

Application of variables control charts to risk-adjusted time-ordered healthcare data.

In a previous article (M. K. Hart, Qual Manag Health Care. 2003;12(1):5-19), the authors presented risk-adjusted control charts applicable for attributes data. The present article discusses a similar class of control charts applicable for variables data that are often skewed. The key feature of these charts is their application of risk-adjusted data in addition to actual performance data. The resulting charts should decrease the occurrence of both type I and type II errors as compared to the unadjusted control charts. This article presents several control charts that vary in the data transformation and combination approaches. Data depicting hospital length of stay following coronary artery bypass graft procedures were used to illustrate the use of transformed and risk-adjusted control charts.

Confounding Factors, Epidemiologic↗
PubMed1989

Objective and subjective attractiveness and early adolescent adjustment.

Using data from the Pennsylvania Early Adolescent Transitions Study (PEATS), this study assessed how objective physical attractiveness (PA), indexed by appraisals from others, and subjective PA, indexed by self-appraisals, relate to each other and, in turn, to early adolescent adjustment (indexed by self-esteem and anxiety). Findings indicated a low relationship between objective and subjective PA. Only subjective PA was associated with adjustment.

Adaptation, Psychological↗
PubMed1998

Health status of Asian Americans: United States, 1992-94.

OBJECTIVES: This report compares the health status of selected Asian national origin groups. METHODS: 1992-94 National Health Interview Survey (NHIS) data were analyzed for six Asian national origin groups (Chinese, Filipino, Asian Indian, Japanese, Vietnamese, and Korean), the Asian and Pacific Islander (API) population as a whole, and the non-Hispanic white population. Unadjusted and age-adjusted estimates and standard errors of health indicators and sociodemographic characteristics were generated. A broad range of health issues was studied including respondent-assessed health status, activity limitation, physician contacts, restricted activity days, hospital episodes, smoking status, and knowledge of acquired immunodeficiency syndrome (AIDS). RESULTS: A greater age-adjusted percent of Vietnamese (17.2 percent) and Korean (12.8 percent) persons had fair or poor respondent-assessed health status than persons of Chinese, Filipino, and Japanese descent (6.1-7.4 percent). A lower age-adjusted percent of Chinese persons (6.5 percent) experienced activity limitation compared with Filipino, Japanese, and Vietnamese persons (9.4-13.2 percent). Japanese persons (4.9 contacts) had a greater average annual number of physician contacts than Chinese persons (3.1 contacts) after age adjusting the data. When the data were age adjusted, a higher percent of Korean adults (22.5 percent) were current smokers than Chinese (10.0 percent) and Asian Indian adults (8.7 percent). A higher age-adjusted percent of Vietnamese (21.2 percent) and Asian Indian (18.0 percent) adults reported knowing nothing about AIDS compared with Japanese adults (5.1 percent). A greater proportion of Vietnamese adults (91.6 percent) had not been tested for the AIDS virus infection compared with Chinese, Filipino, Asian Indian, and Japanese adults (72.6-78.5 percent) after age adjusting the data. CONCLUSIONS: Differences in health emerge when data on the API population are analyzed by national origin group. Estimates of health presented for the API population as a whole mask differences among subgroups.

Acquired Immunodeficiency Syndrome↗
PubMed2005

Mortality after noncardiac surgery: prediction from administrative versus clinical data.

BACKGROUND: Hospital profiles are increasingly constructed using risk-adjusted clinical data abstracted from patient records. OBJECTIVE: We sought to compare hospital profiles based on risk adjusted death within 30 days of surgery from administrative versus clinical data in a national cohort of surgical patients. DESIGN: This was a cohort study that included 78,546 major noncardiac operations performed between October 1, 1991 and December 31, 1993 in 44 Veterans Affairs hospitals. Administrative data were used to develop and validate multivariable logistic regression models of 30-day postoperative death for all surgery and 4 surgical specialties (general, orthopedic, thoracic, and vascular). Previously developed and validated clinical models were obtained and reproduced for matching operations using data from the VA National Surgical Quality Improvement Program. Observed-to-expected 30-day mortality ratios for administrative and clinical data were calculated and compared for each hospital. RESULTS: In multivariable logistic regression models using administrative data, characteristics such as patient age, race, marital status, admission from a nursing home, interhospital transfer, admission on the weekend, weekend surgery, and risk strata consisting of groups of principal and comorbidity diagnoses were predictive of postoperative mortality (P <0.05). Correlations of the clinical and administrative observed-to-expected ratios were 0.75, 0.83, 0.64, 0.78, and 0.86 for all surgery, general, orthopedic, thoracic, and vascular surgery, respectively. When compared with clinical models, administrative models identified outlier hospitals with sensitivity of 73%, specificity of 89%, positive predictive value of 51%, and negative predictive value of 96%. CONCLUSIONS: Our data suggest that risk adjustment of mortality using administrative data may be useful for screening hospitals for potential quality problems.

Aged↗
PubMed2001

Threshold analysis of selected dose-response data for endocrine active chemicals.

Using a biologically relevant mathematical model, the Michaelis-Menten equation, we examined published data from endocrine active chemicals for evidence of no-threshold dose-response curves. Data were fit to a modified Michaelis-Menten equation which accounted for total background response. Subsequently, the data sets were analyzed using non-linear regression in order to estimate the four parameters of interest (non-hormone controlled background (Bnh), maximum response (Rmax), endogenous hormone level (D0), and the dose at which a half-maximal response was observed (ED50)) and to determine the fit to the fully modified Michaelis-Menten equation. Subsequently, response data were adjusted to account for Bnh and then normalized to Rmax, while dose data were adjusted to account for D0 and then normalized to the ED50. This data set was combined into a single, composite data set and fit to the fully modified Michaelis-Menten equation. We examined 31 data sets (24 endpoints) from studies on 9 different chemical/hormone treatments. Twenty-six of the data sets fit the modified Michaelis-Menten equation with high multiple correlation coefficients (r>0.90). The normalized data demonstrated a good fit to the modified Michaelis-Menten equation. These results indicate that a variety of biological responses fit the modified Michaelis-Menten equation, which does not have a threshold dose term.

Dose-Response Relationship, Drug↗
PubMed2004

Age-adjustment in experimental animal data and its application to lung cancer in radon-exposed rats.

Procedures for age-adjustment of cancer fractions are proposed which do not require fixed age intervals. The full available information on survival times can then be used, which is especially important in small treatment groups. For incidental cancers a non-decreasing prevalence function and for fatal cancers the Kaplan-Meier estimator is used. In the latter case, the estimated competing risk of the control population is standardized, not its true survival. This makes the technique also applicable to treatment groups with high incidence, which otherwise may give adjusted rates above 100%. In the application part these age-adjustment techniques are used here to study lung cancer in radon-exposed Wistar and Sprague-Dawley rats. The data include a classification in fatal and incidental lung cancers. For fatal lung cancer, the lifetime excess absolute risk (LEAR) at 1 WLM averaged over all exposed groups is 0.67x10(-4) for the Wistar rats, while for the Sprague-Dawley rats it is 0.40x10(-4). For the Sprague-Dawley rats, there are several groups exposed later in life. When the averaging is restricted to animals with start of exposure prior to 150 days of age, the weighted average risk among the Sprague-Dawley rats is 0.79x10(-4). Compared to groups with similar exposures as young adults (up to about 150 days), animals exposed later in life have substantially lower lifetime risks. The Wistar rats include groups with roughly equal exposure rates and ages at start of exposure, but with increasing exposure duration. Within these groupings the LEAR at 1 WLM does not decrease with additional exposure at higher age, as would be expected if the risk from exposures at different ages would be additive.

Administration, Inhalation↗
PubMed2002

Good things come in threes: single-parent multigenerational family structure and adolescent adjustment.

Using data from the National Educational Longitudinal Study (NELS), we found that teenagers who live in nonmarried families are less likely to graduate from high school or to attend college, more likely to smoke or drink, and more likely to initiate sexual activity. Not all nonmarried families are alike, however. In particular, teenagers living with their single mothers and with at least one grandparent in multigenerational households have developmental outcomes that are at least as good and often better than the outcomes of teenagers in married families. These findings obtain when a wide array of economic resources, parenting behavior, and home and school characteristics are controlled for.

Adolescent↗
PubMed1991

Comparison of energy expenditure in men and women at rest and during exercise recovery.

The purpose of this study was to compare the energy expenditure (EE) of men and women at rest and during a 1 h recovery from 30 min of exercise at 40% of VO2max. Subjects were five physically active lean men (mean age, % fat, and VO2max = 34.8 +/- 8.1 years, 8.1 +/- 3.2% and 63.8 +/- 8 ml.kg-1.min-1, respectively) and five physically active lean women (mean age, % fat, and VO2max = 26.2 +/- 5.1 years, 17.6 +/- 4.5%, and 50.2 +/- 13.6 ml.kg-1.min-1, respectively). Energy expenditure (EE) was measured continuously by standard open circuit spirometry for 20 min at rest and for 1 h immediately after 30 min of exercise at 40% of VO2max. Independent t tests and ANCOVA were used to compare EE of men and women at rest and during exercise recovery. EE at rest in the men was significantly greater using a t test (p less than .05) than in the women but it was not when the data were adjusted with ANCOVA using body weight, VO2max in ml.kg-1.min-1, and percent body fat as covariates. The EE during 1 h of recovery was also significantly higher in the men using a t test (p less than .05) and after the data were adjusted for differences in VO2max (p less than .02). With body weight and percent fat as covariates. The EE during 1 h of recovery was also significantly higher in the men using a t test (p less than .05) and after the data were adjusted for differences in VO2max (p less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2006

Regression analysis of mean quality-adjusted lifetime with censored data.

In clinical trials of chronic diseases such as acquired immunodeficiency syndrome, cancer, or cardiovascular diseases, the concept of quality-adjusted lifetime (QAL) has received more and more attention. In this paper, we consider the problem of how the covariates affect the mean QAL when the data are subject to right censoring. We allow a very general form for the mean model as a function of covariates. Using the idea of inverse probability weighting, we first construct a simple weighted estimating equation for the parameters in our mean model. We then find the form of the most efficient estimating equation, which yields the most efficient estimator for the regression parameters. Since the most efficient estimator depends on the distribution of the health history processes, and thus cannot be estimated nonparametrically, we consider different approaches for improving the efficiency of the simple weighted estimating equation using observed data. The applicability of these methods is demonstrated by both simulation experiments and a data example from a breast cancer clinical trial study.

Breast Neoplasms↗
PubMed2001

Evaluation of an adjusted chi-square statistic as applied to observational studies involving clustered binary data.

A simple adjustment to the Pearson chi-square test has been proposed for comparing proportions estimated from clustered binary observations. However, the assumptions needed to assure the validity of this test have not yet been thoroughly addressed. These assumptions will hold for experimental comparisons, but could be violated for some observational comparisons. In this paper we investigate the conditions under which the adjusted chi-square statistic is valid and examine its performance when these assumptions are violated. We also introduce some alternative test statistics that do not require these assumptions. The test statistics considered are then compared through simulation and an example presented based on real data. The simulation study shows that the adjusted chi-square statistic generally produces empirical type I errors close to nominal under the assumption of a common intracluster correlation coefficient. Even if the intracluster correlations are different, the adjusted chi-square statistic performs well when the groups have equal numbers of clusters.

Chi-Square Distribution↗