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PubMed2000

Parametric empirical Bayes estimates of disease prevalence using stratified samples from community populations.

Studies of chronic diseases in a community setting often employ stratified sample designs to enable the study to attain multiple research goals at a reasonable cost. One important goal is estimation of disease prevalence in the whole community and in important subgroups. Some adjustment for the sample design is necessary; if the design has many strata with very disparate sampling fractions, simply upweighting observed stratum prevalences may lead to unstable estimators. We propose a parametric empirical Bayes estimator in the spirit of the work of Efron and Morris, and we compare it to the direct upweighted estimator and a regression-smoothed estimator. Simulation studies in realistic settings suggest that the new estimator performs best, giving estimates with low bias and good precision under a variety of models.

Age Factors↗
PubMedDate not supplied

Overview of important design issues for a National Human Exposure Assessment Survey.

Exposure issues have important consequences for regulatory decisions. Reliable answers to exposure questions are critical for site cleanup, model validation, and cumulative risk issues, as well as giving perspective on our risk estimates. This paper discusses some of the important issues in designing the National Human Exposure Assessment Survey (NHEXAS) and, by implication, other exposure-monitoring-based studies as well. Sampling design issues are discussed in terms useful to exposure assessors. These issues include simple random sample designs versus more complex multistage designs, design efficiency, how to determine the sample size for the desired precision of the estimate, and the effects of stratification and oversampling on the needed sample size. This paper also discusses several important nonsampling issues such as population definition, response rates, and several potential sources of error in interpreting the monitoring results.

Data Collection↗
PubMed2001

Design evaluation for a population pharmacokinetic study using clinical trial simulations: a case study.

Clinical trial simulations were conducted to assess power and sample size requirements for a population pharmacokinetic (PK) substudy of a phase III clinical trial. The simulations were based on a population PK model developed from phase I healthy volunteer data. A sparse sampling design was employed taking into account the practical considerations regarding the desire not to keep patients at the study sites for extended periods of time for blood sampling. It was expected that the sparse sampling design would not support fitting the same model developed in healthy volunteers due to the narrow range of sampling times. Therefore, a model with fewer parameters and variance components was fit to simulated data from the proposed design to assess the bias in the estimates of the population mean PK parameters and variance components. Results indicate that the proposed design employing the simple model can provide accurate mean estimates of oral drug clearance (CL) and the apparent steady-state volume of distribution (V(ss)). However, the simulation results also suggest that the size and power of the likelihood ratio test for subpopulation differences in CL are inflated when using the simple model.

Clinical Trials, Phase I as Topic↗
PubMed2001

Effects of age on validity of self-reported height, weight, and body mass index: findings from the Third National Health and Nutrition Examination Survey, 1988-1994.

OBJECTIVE: To compare self-reported to measured heights and weights of adults examined in the Third National Health and Nutrition Examination Survey (NHANES III), and to determine to what extent body mass index (BMI) calculated from self-reported heights and weights affects estimates of overweight prevalence compared with BMI calculated from measured values. DESIGN: A complex sample design was used in NHANES III to obtain a nationally representative sample of the US civilian, noninstitutionalized population. During household interviews, survey respondents were asked their height and weight. Trained health technicians subsequently measured height and weight using standardized procedures and equipment. SUBJECTS: The analytical sample consisted of 7,772 men and 8,801 women 20 years old and older. STATISTICAL ANALYSES PERFORMED: Only persons with measured and self-reported heights and weights were included in the analysis, and statistical sampling weights were applied. t Tests, Pearson product moment correlation coefficients, sensitivity, and specificity analyses were used to determine the validity of self-reported measurements and prevalence estimates of overweight, defined as BMI of 25 or greater. RESULTS: Age is an important factor in classifying weight, height, BMI, and overweight from self-reports. Statistically significant differences were found for the mean error (measured-self-reported values) for height and BMI that were notably larger for older age groups. For example, the mean error for height ranged from 2.92 to 4.50 cm for women and from 3.06 to 4.29 cm for men, 70 years and older. Despite the high correlation between measured and self-reported data, the prevalence of overweight calculated from measured values was higher than that calculated from self-reported values among older adults. When calculated with self-reported height, BMI was one unit lower than when calculated from measured height for persons > or = 70 years. Specificity was high but sensitivity decreased with increasing age cohorts. Regression equations are provided to determine actual height from self-reported values for older adults. CONCLUSION/APPLICATIONS: Self-reported heights and weights can be used with younger adults, but they have limitations for older adults, ages > or = 60 years. In research studies and in clinical settings involving older adults, failure to measure height and weight can result in subsequent misclassification of overweight status. Therefore, registered dietitians are encouraged to obtained a measured weight and height using a calibrated scale and stadiometer.

Adult↗
PubMed1997

ICS-II USA research design and methodology.

The purpose of the WHO-sponsored International Collaborative Study of Oral Health Outcomes (ICS-II) was to provide policy-markers and researchers with detailed, reliable, and valid data on the oral health situation in their countries or regions, together with comparative data from other dental care delivery systems. ICS-II used a cross-sectional design with no explicit control groups or experimental interventions. A standardized methodology was developed and tested for collecting and analyzing epidemiological, sociocultural, economic, and delivery system data. Respondent information was obtained by household interviews, and clinical examinations were conducted by calibrated oral epidemiologists. Discussed are the sampling design characteristics for the USA research locations, response rates, samples size for interview and oral examination data, weighting procedures, and statistical methods. SUDAAN was used to adjust variance calculations, since complex sampling designs were used.

Adult↗
PubMed1991

Assessment of long-term exposures to toxic substances in air.

Because airborne exposure varies greatly over time and between individual workers, occupational hygienists should adopt sampling strategies which recognize the inherent statistical nature of assessing exposure. This analysis indicates that the traditional practice of testing 'compliance' with occupational exposure limits (OELs) should be discarded. Rather, it is argued that acceptable exposure should be defined with reference to the exposure distribution. Regarding the many statistical issues which come into play, it is concluded that hygienists should continue to apply the log-normal model for summarizing and testing data. However, sampling designs should move away from methods which are biased (e.g. sampling only the worst case) and which rely upon job title and observation as the primary means of assigning workers into groups. Since exposure data often lack independence (e.g. owing to the autocorrelation of serial measurements) and there exist large differences in exposure between workers in the same job group, random sampling designs should be adopted. It is also shown that the relationship between the mean of a log-normal distribution and exposures in the right tail allows one to evaluate simultaneously the mean exposure and the maximum frequency with which exposures exceed the OEL. Investigation of the biological concepts relies heavily upon a conceptual model which depicts the exposure-response continuum as a sequence of time series related to exposure, burden, damage and risk. Analysis of the linkages between these processes identifies two kinetic conditions which are necessary if variability of exposure is to affect appreciably the individual's risk of chronic disease. First, the variation of exposure from interval to interval must be efficiently translated into burden and damage (no damping), and second, during periods of intense exposure the relationship between burden and damage must be non-linear (curving upwards). On the basis of current knowledge it appears that relatively few chronic toxicants satisfy both these conditions. Even for those substances which cause damage only when a threshold is exceeded, a statistical argument suggests that the maximum risk can still be related to the mean exposure received over time. It is concluded that the risk of chronic disease generally depends upon the mean exposure received by the individual worker over time. Thus, the sampling strategy must allow the distribution of individual mean exposures to be characterized across the population at risk. It follows from this paradigm for assessing exposures that relatively little effort should be devoted to the evaluation of short-term 'peak' exposures since such transients are unlikely to exert undue influence on long-term effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Air Pollutants, Occupational↗
PubMed1997

Design for sample size re-estimation with interim data for double-blind clinical trials with binary outcomes.

Estimation of sample size in clinical trials requires knowledge of parameters that involve the treatment effect and variability, which are usually uncertain to medical researchers. The recent release within the European Union of a Note for Guidance from the Commission for Proprietary Medical Products (CPMP) highlights the importance of this issue. Most previous papers considered the case of continuous response variables that assume a normal distribution; some regarded the portion up to the interim stage as an 'internal pilot study' and required unblinding. In this paper, our concern is with the case of binary response variables, which is more difficult than the normal case since the mean and variance are not distinct parameters. We offer a design with a simple stratification strategy that enables us to verify and update the assumption of the response rates given initially in the protocol. The design provides a method to re-estimate the sample size based on interim data while preserving the trial's blinding. An illustrative numerical example and simulation results show slight effect on the type I error rate and the decision making characteristics on sample size adjustment.

Clinical Trials as Topic↗
PubMed2000

Integrated sample collection and handling for drug discovery bioanalysis.

An integrated sample handling process for drug discovery bioanalysis is described. The streamlining of study design, sample collection and automatic bioanalytical sample processing is demonstrated. Specific details for the entire procedure regarding the time saved, ease of automation and integration are defined. Details of sample handling involved a sample collection map, sample collection formatting and volume, dilution schemes for high concentration samples, choice of biological fluid and evaluating the capabilities of two liquid-handling workstations. Numerous comparisons were conducted between the new approaches and the conventional sample handling approaches. The precision and accuracy obtained from the new integrated sample handling process were comparable to those obtained from a conventional approach, as were pharmacokinetic profiles and parameters. This new sampling process greatly improved the efficiency of drug discovery bioanalysis. The integration of pre-clinical protocol design, sample collection and bioanalysis processes was also achieved.

Animals↗
PubMed2001

The relationship between pharmacists' tenure in community setting and moral reasoning.

OBJECTIVE: To explore the relationship between pharmacists' tenure in the community setting and their moral reasoning abilities. DESIGN: Systematic random sample design. SETTING: A large southeastern city in the United States. PARTICIPANTS: 450 independent and chain community pharmacists identified from the state board of pharmacy list of licensed community pharmacists. INTERVENTIONS: A mailed questionnaire that included a well-known moral reasoning instrument and collected demographic information. MAIN OUTCOME MEASURES: Moral Reasoning abilities and tenure of community pharmacists. RESULTS: As a group, community pharmacists with greater years of tenure in community practice scored significantly lower on moral reasoning than those pharmacists with fewer years of tenure (p=0.016). CONCLUSION: Four plausible explanations for the results are given including: a) a selection of lower ethical reasoners and/or an exodus of higher ethical reasoners from the community setting; b) a retrogression in the moral reasoning skills as community pharmacists obtain tenure in this setting; c) differences between the low and high moral reasoning groups may be due to a cohort effect; and d) the obtained practitioner sample may not have been representative of the population of community pharmacists.

Community Pharmacy Services↗
PubMed1991

Sequential or fixed sample trial design? A case study by stochastic simulation.

The properties of Wilcoxon's rank sum test for fixed sample size and a Wilcoxon-type two-sample sequential test have been illustrated and compared by means of stochastic simulation. Data from a real fixed sample trial have been used, both for resampling from the original data, and for construction of an idealized theoretical distribution. The sequential and the fixed sample test obtain equal power, but the sequential test mostly includes considerably fewer patients to reach a conclusion, i.e. the mean and median number of patients included are both much lower than the fixed sample size. Under the hypotheses only a small fraction of the simulation runs exceed the fixed sample size. These findings exemplify results obtained in theoretical analyses and simulation studies covering a wide range of distributions. In our opinion sequential tests have obvious advantages and are in many cases better alternatives than fixed sample tests in clinical trials.

Clinical Trials as Topic↗
PubMed1994

Evaluating peer reviews. Pilot testing of a grading instrument.

OBJECTIVE: To measure the reliability and preliminary validity of a grading instrument for editors to evaluate the quality of peer reviews. DESIGN: The consecutive sample design included 53 reviews of 23 manuscripts. Reviews were systematically assigned to interrater reliability (n = 41; power greater than 0.90 to detect a difference of greater than one point) and preliminary criterion-related validity (n = 12) subsamples. Content validity was closely examined. SETTING: Nonclinical. PARTICIPANTS: Three graders evaluated reliability. One individual examined content validity and two editors tested preliminary criterion-related validity. INTERVENTION (INSTRUMENT)--Attributes reflecting two basic dimensions, review content and format, were identified and scored (values are possible points/percent contribution): timeliness, 3/21%; grade sheet, 1/7%; etiquette, 1/7%; sectional narratives, 3/21%; citations, 2/14%; narrative summary, 2/14%; and insights, 2/14%. A scoring guide was provided. MAIN OUTCOME MEASURES: Statistical analyses used to test the interrater reliability of the total score included the intraclass correlation coefficient and analysis of variance with the expectation to uphold the null hypothesis. Kendall's coefficient of concordance was used to test preliminary criterion-related validity. RESULTS: The intraclass correlation coefficient was .84 (P < .001) and a lack of difference between mean scores was demonstrated by analysis of variance (P = .46). Content validity was confirmed and preliminary criterion-related validity was indicated (Kendall's coefficient of concordance = .94, P = .038). CONCLUSIONS: The instrument is reliable. Content validation has been completed, and further criterion-related validation is warranted.

Evaluation Studies as Topic↗
PubMed1988

D-optimal design applied to binding saturation curves of an enkephalin analog in rat brain.

The D-optimal design, a minimal sample design that minimizes the volume of the joint confidence region for the parameters, was used to evaluate binding parameters in a saturation curve with a view to reducing the number of experimental points without loosing accuracy in binding parameter estimates. Binding saturation experiments were performed in rat brain crude membrane preparations with the opioid mu-selective ligand [3H]-[D-Ala2,MePhe4,Gly-ol5]enkephalin (DAGO), using a sequential procedure. The first experiment consisted of a wide-range saturation curve, which confirmed that [3H]-DAGO binds only one class of specific sites and non-specific sites, and gave information on the experimental range and a first estimate of binding affinity (Ka), capacity (Bmax) and non-specific constant (k). On this basis the D-optimal design was computed and sequential experiments were performed each covering a wide-range traditional saturation curve, the D-optimal design and a splitting of the D-optimal design with the addition of 2 points (+/- 15% of the central point). No appreciable differences were obtained with these designs in parameter estimates and their accuracy. Thus sequential experiments based on D-optimal design seem a valid method for accurate determination of binding parameters, using far fewer points with no loss in parameter estimation accuracy.

Animals↗
PubMed1999

Sample size and design considerations for phase II clinical trials with correlated observations.

Several methods are available for the design of phase II clinical trials with binary endpoints. A primary assumption for most methods is that observations on the endpoint of interest are uncorrelated; however, this assumption is violated if an individual patient provides more than one observation on the endpoint of interest. In such cases, one solution is to use a summary measure for each patient; an alternative solution is to perform an observation-specific analysis using a technique that properly accounts for the correlation. In this paper, we investigate the effect that ignoring correlated observations can have on the design properties of the typical phase II clinical trial. In cases in which an observation-specific analysis is desirable, we propose a simple method that adjusts a standard one- or two-stage phase II design to account for loss of information due to correlated observations. Simulations demonstrate that the method ensures that type I and type II error rate design requirements are met even in the presence of strong correlation. We develop the method in the context of phase II oncology trials, but the method applies readily to other clinical areas in which multiple responses per patient are of interest.

Algorithms↗
PubMedDate not supplied

Situational factors as determinants of community pharmacists' clinical decision making behavior.

OBJECTIVE: To examine the relative contribution of two work-related pressures, workload and perceived normative beliefs of significant others, to community pharmacists' clinical decision making behavior. DESIGN: Systematic random sample design. SETTING: A large southeastern city. PARTICIPANTS: 450 independent and chain community pharmacists identified from the state board of pharmacy list of licensed community pharmacists. INTERVENTIONS: A mailed questionnaire asking about community pharmacists' workload pressures and the perceived beliefs of their patients and employers (significant others) approving or disapproving of them providing pharmaceutical care. MAIN OUTCOME MEASURES: Clinical decision making behavior, as measured using a subset of the Behavioral Pharmaceutical Care Scale. RESULTS: Response rate was 31.8%. Workload was not significantly related to clinical decision making. After controlling for social desirability and workload, perceived normative beliefs of significant others was highly significant; it accounted for 7.6% of the variance associated with clinical decision making behavior. CONCLUSION: Workload pressures did not appear to influence the provision of pharmaceutical care. Community pharmacists' perceived normative beliefs about their patients' and employer's approval or disapproval of the provision of pharmaceutical care should be further examined within the larger context of the pharmacy organization's climate.

Adult↗
PubMed2000

The association between abuse in childhood and STD/HIV risk behaviours in female genitourinary (GU) clinic attendees.

OBJECTIVES: To compare and contrast women with a history of child abuse with those who have no history of child abuse on STI/HIV risk behaviours and safer sex beliefs in an inner city UK sample. DESIGN: Cross sectional sample survey. METHODS: Routine female clinic attendees were invited to complete an anonymous self report questionnaire which included background information, sexual and drug risk behaviour, self reported sexually transmitted infections (STIs), psychological distress (Hospital and Anxiety Depression Scale; HADS), Sexual Risk Cognitions Questionnaire (SRCQ), and history of child sexual, physical, and emotional abuse. RESULTS: 137 (45%) of 303 women reported a history of child abuse; all three forms of child abuse--sexual (26%), physical (20%), and emotional (27%) abuse--overlapped. The majority of women reported one sexual partner in the past month, and the majority did not use condoms. Women reporting a history of child abuse were more likely to have had previous STIs (p = 0.007) and to have had more than one STI (p = 0.04) compared with women who had not experienced child abuse. Injecting drug use and commercial sex work were of low prevalence across the whole sample and no group differences were found. Women reporting a history of child abuse had higher HADS anxiety (p = 0.03) compared with women with no history of child abuse. Confidence in using condoms with a sexual partner was not related to child abuse. Women with a history of child abuse reported significantly higher frequency of thoughts reflecting anticipated negative reactions from partners to suggesting condom use (p = 0.02) and judging a partner's risk by their appearance (p = 0.05) compared with women with no history of child abuse. CONCLUSIONS: Comparable rates of child sexual abuse with US studies were found in this UK inner city population of women attending sexual health services. Women who had experienced child abuse were more likely to report ever having had an STI and having had more than one STI. Complex psychological and social factors contribute to difficulties for women in negotiating safer sex including emotional distress, abuse histories, and anticipating a negative reaction from partners. Multifaceted prevention models are needed.

Adolescent↗
PubMed1996

Should amenorrhoea be necessary for the diagnosis of anorexia nervosa? Evidence from a Canadian community sample.

BACKGROUND: This study compares the characteristics of women with anorexia nervosa with those of women who have all the diagnostic features of that disorder except amenorrhoea. METHOD: The study uses data from a large community epidemiological survey of the mental health status of household residents in Ontario, Canada. A multi-stage stratified sampling design generated a sample of 4285 females aged 15-64. DSM-III-R diagnoses were made using the Composite International Diagnostic interview. RESULTS: Eighty-four out of 4285 female respondents met full or partial-syndrome criteria for anorexia nervosa. Comparison of these two groups revealed few statistically significant differences in terms of demographics, psychiatric comorbidity, family history or early experiences. CONCLUSIONS: Amenorrhoea did not discriminate between women with anorexia nervosa and women with all the features except amenorrhoea across a number of relevant variables. The authors question the utility of amenorrhoea as a diagnostic criterion.

Adolescent↗
PubMed2002

Linkage for platelet monoamine oxidase (MAO) activity: results from a replication sample.

BACKGROUND: Monoamine oxidase B (MAO-B) degrades catecholamines in presynaptic nerve endings and is also active in platelets. There is evidence to suggest that platelet MAO-B activity level is controlled by a major genetic locus distinct from the structural gene on the X chromosome. To expand on a prior report, new linkage analyses for platelet MAO-B activity have been performed on the previously analyzed sample (designated the initial sample), on a new sample of families (the replication sample), and on the combined sample. These families were recruited as part of the Collaborative Study on the Genetics of Alcoholism (COGA). METHODS: The initial sample consists of 105 extended families providing 1002 nonindependent (412 independent) sib pairs that have been phenotyped for MAO activity and genotyped. The replication sample of 157 extended families contains 608 nonindependent (309 independent) phenotyped and genotyped sib pairs. Analyses were conducted using Haseman-Elston based regression on sib pairs and variance component analysis on extended pedigrees, and the importance of cigarette smoking and gender as covariates of platelet MAO-B activity was taken into account. RESULTS: Regions on chromosomes 2, 9, and 12 indicated consistent evidence for linkage across the two distinct datasets by at least one analysis method. Under Haseman-Elston regression of independent sib pairs, only the chromosome 2 region gave lod scores above 1 in both the initial and replication samples. Using all possible pairs, unweighted, for the regression, chromosome 12 gave lod scores above 1 in both samples. For variance component analysis, only the chromosome 9 region gave lod scores above 1 in both samples. CONCLUSIONS: The consistency across datasets of these findings is encouraging. In particular, variance component analysis of extended pedigrees supports a potential linkage of MAO-B activity to chromosome 9, with a lod over 3 at 115 cM near D9S261 in the combined sample. Sib-pair regression supports this finding with modest lod scores in the region. Suggestive linkage to chromosomes 2 and 12 from sib-pair analysis is only weakly supported by variance component analysis.

Blood Platelets↗
PubMed1998

Evaluation of an acriflavine disk assay for differentiating Staphylococcus aureus from other staphylococci isolated from bovine milk.

OBJECTIVE: To develop an acriflavine disk assay for identification of Staphylococcus aureus and to test whether the acriflavine disk assay could be used to differentiate S aureus from other staphylococci isolated from bovine milk samples. DESIGN: Prospective study. SAMPLE POPULATION: 882 staphylococcal isolates from bovine milk samples and 3 S intermedius isolates from dogs. PROCEDURE: Paper disks saturated with various amounts of acriflavine were used in a growth inhibition assay to determine the amount of acriflavine that would most reliably differentiate S aureus from other staphylococci. For all isolates, hemolytic pattern, results of tube coagulase tests after 4 and 24 hours of incubation, growth on acriflavine-supplemented media, results of an acriflavine disk assay, and results of an automated identification system were determined. RESULTS: 10 micrograms of acriflavine/disk was determined to be the most appropriate concentration for use in the assay. All 112 isolates identified as S aureus by the automated identification system were resistant to this concentration of acriflavine, and only 1 of 236 isolates identified as non-S aureus staphylococci was resistant. There was substantial agreement between results of using the acriflavine disk assay as a diagnostic criterion for differntiating S aureus isolates from non-S aureus staphylococci and results of the automated identification system. Agreement between results of determining hemolytic pattern and results of other diagnostic tests was only moderate. CLINICAL IMPLICATIONS: The acriflavine disk assay, using 10 micrograms of acriflavine/disk, was a practical, accurate method for differentiating S aureus isolates from non-S aureus staphylococci.

Acriflavine↗