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PubMed1975

Ovarian changes during early pregnancy in pony mares in relation to PMSG production.

The ovaries of twenty pregnant mares were examined daily, per rectum, for the first 4 months of gestation and note was made of their estimated size and follicular content. Serial blood samples from sixteen of the mares were assayed for PMSG. A marked seasonal effect was noted on ovarian size, follicular content and ovulation rate during pregnancy but there was no such effect on PMSG production. It is concluded that PMSG is synergistic with gonadotrophins of pituitary origin and that the latter hormone are the primary stimulus on the ovary of the pregnant horse.

Animals↗
PubMed2004

Using survey data for diabetes surveillance among minority populations: a report of the Centers for Disease Control and Prevention's expert panel meeting.

INTRODUCTION: Data on diabetes morbidity and mortality and the quality of care among U.S. minority populations are necessary to assess progress toward eliminating racial/ethnic disparities and to design and implement effective interventions. This paper summarizes the discussions and recommendations of an expert panel to address the use of survey data for diabetes surveillance among minority populations. METHODS: The Centers for Disease Control and Prevention's Division of Diabetes Translation convened an expert panel of persons with survey experience and awareness of the problems in conducting health-related surveys among minority populations. Panel members were asked to 1) determine ways to enhance the ability of existing survey systems to address diabetes surveillance among minority populations; 2) identify survey systems that could be used to address surveillance needs; and 3) determine whether new minority-specific survey systems need to be developed. RESULTS: Panel members concluded that, although no existing survey system is completely adequate for diabetes surveillance among minority populations, new systems should not be developed. They recommended 1) investigating the use of community-based surveys; 2) exploring the ability of national surveys to increase sample sizes and produce state-level estimates; and 3) encouraging government agencies and public health programs to coordinate and integrate diabetes-related survey data and share analytic methodology. CONCLUSION: No existing survey is suitable for conducting minority-specific diabetes surveillance. Modifying and expanding existing surveys to establish a diabetes surveillance system of sentinel minority populations would be more feasible than developing a new one. Interagency coordination and collaboration will be critical in this effort.

Centers for Disease Control and Prevention, U.S.↗
PubMed1992

Osteoarthritis antirheumatic drug trials. III. Setting the delta for clinical trials--results of a consensus development (Delphi) exercise.

Defining the minimum clinically important difference or delta to be detected in a clinical trial depends on a number of factors including the research hypothesis, patient characteristics, the nature of the intervention and the trial design. In 2 studies, we have developed standardized procedures for conducting outcome measurement based on current Food and Drug Administration and European League Against Rheumatism guidelines for osteoarthritis clinical trials, and determined the standard deviation for these outcome measures. In the final component of this series of studies, we have used a Delphi technique to establish estimates for delta, and calculated the sample size requirements under 2 different conditions of Type I and Type II error probabilities.

Clinical Trials as Topic↗
PubMedDate not supplied

Sampling almonds for aflatoxin, part I: estimation of uncertainty associated with sampling, sample preparation, and analysis.

Domestic and international regulatory limits have been established for aflatoxin in almonds and other tree nuts. It is difficult to obtain an accurate and precise estimate of the true aflatoxin concentration in a bulk lot because of the uncertainty associated with the sampling, sample preparation, and analytical steps of the aflatoxin test procedure. To evaluate the performance of aflatoxin sampling plans, the uncertainty associated with sampling lots of shelled almonds for aflatoxin was investigated. Twenty lots of shelled almonds were sampled for aflatoxin contamination. The total variance associated with measuring B1 and total aflatoxins in bulk almond lots was estimated and partitioned into sampling, sample preparation, and analytical variance components. All variances were found to increase with an increase in aflatoxin concentration (both B1 and total). By using regression analysis, mathematical expressions were developed to predict the relationship between each variance component (total, sampling, sample preparation, and analysis variances) and aflatoxin concentration. Variance estimates were the same for B1 and total aflatoxins. The mathematical relationships can be used to estimate each variance for a given sample size, subsample size, and number of analyses other than that measured in the study. When a lot with total aflatoxins at 15 ng/g was tested by using a 10 kg sample, a vertical cutter mixer type of mill, a 100 g subsample, and high-performance liquid chromatography analysis, the sampling, sample preparation, analytical, and total variances (coefficient of variation, CV) were 394.7 (CV, 132.4%), 14.7 (CV, 25.5%), 0.8 (CV, 6.1%), and 410.2 (CV, 135.0%), respectively. The percentages of the total variance associated with sampling, sample preparation, and analytical steps were 96.2, 3.6, and 0.2, respectively.

Aflatoxin B1↗
PubMed1991

Ankylosing spondylitis antirheumatic drug trials. III. Setting the delta for clinical trials of antirheumatic drugs--results of a consensus development (Delphi) exercise.

Defining the minimum clinically important difference or delta to be detected in a clinical trial depends on a number of factors including the research hypothesis, patient characteristics, the nature of the intervention and the trial design. In 2 previous studies, we have developed standardized procedures for conducting outcome measurement based on current Food and Drug Administration and European League Against Rheumatism guidelines for clinical trials in ankylosing spondylitis, and thereafter, determined the standard deviation for these outcome measures. In the final component of this series of studies, we have employed a Delphi technique to establish estimates for delta, and calculated the sample size requirements under 2 different conditions of Type I and Type II error probabilities.

Anti-Inflammatory Agents↗
PubMed1991

Rheumatoid arthritis antirheumatic drug trials. III. Setting the delta for clinical trials of antirheumatic drugs--results of a consensus development (Delphi) exercise.

Defining the minimum clinically important difference or delta to be detected in a clinical trial depends on a number of factors including the research hypothesis, patient characteristics, the nature of the intervention and the trial design. In 2 previous studies, we have developed standardized procedures for conducting outcome measurement based on current Food and Drug Administration and European League Against Rheumatism guidelines for RA clinical trials, and thereafter, determined the standard deviation for these outcome measures. In the final component of this series of studies, we employed a Delphi technique to establish estimates for delta and calculated the sample size requirements under different conditions of Type I and Type II error probabilities.

Arthritis, Rheumatoid↗
PubMed1996

Heritability estimate of hypertrophic cardiomyopathy in pigs (Sus scrofa domestica).

The purpose of this study was to evaluate the heritability of hypertrophic cardiomyopathy (HCM) in pigs and the relation between HCM and heart measurements, pathologic features, and growth to provide references for HCM line development. A total of 353 on-farm tested gilts (females) and boars (males) from 74 sire families were randomly selected from a single breeding farm where HCM was prevalent. Hearts were collected after animals were slaughtered. Heart length, width, and weight, heart-to-body weight ratio, and thickness of the cranial, middle, and caudal portions of the ventricular septum, left and right ventricles, and apex were measured. Cardiac hypertrophy and myocyte disorganization, myocardial and endocardial fibrosis, and intramural coronary arterial occlusion were used as criteria for HCM. Growth traits were evaluated from average daily body weight gain, ultrasonically determined backfat thickness, loin-eye area, and performance selection index. Heritability of the disease was estimated by treating it as a threshold trait. The prevalence of HCM in three studied breeds was 5.26 in Duroc, 22.98 in Landrace, and 5.56% in Yorkshire pigs. The value in Landrace pigs was significantly (P < 0.001) higher than that in the other pigs. There was no significant difference between sexes. In general the heart of pigs with HCM was heavier, wider, longer, and thicker than that of clinically normal pigs. Backfat was the only growth trait with a difference (P < 0.05) among pig breeds. The HCM pigs were leaner than normal pigs. Leaner pigs may have a higher risk of HCM. Heritability of HCM was > 0.30 for all three breeds, but the standard errors of these estimates were high because of limited sample size, in particular for the Yorkshire and Duroc breeds. The preliminary results of this study indicate that HCM in pigs is moderately heritable; thus development of a high-HCM incidence line by selection is possible.

Animals↗
PubMed1998

Human brain tumors and exposure to metal and non-metal elements: a case-control study.

BACKGROUND: Primary brain tumors are among the most deadly of all cancers, with a 1-year survival rate of 52%. Certain elements, such as nickel, cadmium, chromium, arsenic, and beryllium, are established carcinogens in other organs. Silicon and titanium are suspected carcinogens and other elements are known to promote or inhibit the rate of tumor growth. Knowledge about the carcinogenicity of these elements in the brain is limited. In this study, we investigated the potential role of these elements as risk factors for human brain tumors. METHODS: In a case-control study, we assessed brain biopsies from 12 patients with various types of primary brain tumors and in tumor-free brain tissue from 6 autopsy cases. We used energy-dispersive X-ray analysis (EDX) to determine if there were significant differences in the concentration of the study elements in tumors and in control brains. RESULTS: In a bivariate analysis, a statistically significant association was observed between the presence of brain tumors and the concentrations of silicon (p = 0.01), magnesium (p = 0.01), and calcium (p = 0.03). Zinc was also associated with a borderline significance (p = 0.05). No association was observed for nickel (p = 0.74). Although the magnitude of the observed association was estimated using multiple logistic regression analyses, the relative risk estimates were imprecise because of insufficient sample size. Further research using a larger sample size is needed to elucidate the role of these elements in human brain carcinogenesis.

Aged↗
PubMed1996

Precision of benchmark dose estimates for continuous (nonquantal) measurements of toxic effects.

The benchmark dose (BMD) corresponding to a low level of the risk of induced disease, e.g., 1 to 10%, has been proposed by various authors as a replacement for the no observed adverse effect level for noncancer endpoints in the regulation of the conditions of exposure to chemicals. This paper focuses on the variability of estimates of the BMD for nonquantal (continuous measurements) of biological endpoints such as are encountered for hematological data, clinical chemistry, and studies of neurotoxic effects. For biological endpoints that can be described by a normal distribution, estimates of the mean and standard deviation are required to calculate the BMD. Estimates of the standard deviation generally are quite variable, particularly for small sample sizes. The purpose of this paper is to examine the precision of the estimates of risk and of the BMD resulting from the inherent variability of the estimates of the standard deviations particularly for bioassays that employ a small number of animals. When the standard deviation is underestimated, the BMD and the regulatory "safe" dose are underestimated. Conversely, when the standard deviation is overestimated, the BMD and safe dose are overestimated. Overestimation of the BMD can be reduced or eliminated by using a lower confidence limit. The worst cases arise where only a few animals are used per dose and the dose response is supralinear (changes rapidly at low doses and levels off at higher doses). If the standard deviation is constant across doses (for lognormally distributed data if the coefficient of variation is constant), a pooled estimate across doses of the standard deviation can be used. In this case, for bioassays employing a total of 40 to 50 animals, the calculation of the BMD will generally be within a factor of 2 of the true value. When the standard deviation is not constant across dose groups, it is desirable to have more than 10 animals per dose group.

Animals↗
PubMed2006

Locus-specific heritability estimation via the bootstrap in linkage scans for quantitative trait loci.

BACKGROUND/AIMS: In genome-wide linkage analysis of quantitative trait loci (QTL), locus-specific heritability estimates are biased when the original data are used to both localize linkage and estimate effects, due to maximization of the LOD score over the genome. Positive bias is increased by adoption of stringent significance levels to control genome-wide type I error. We propose multi-locus bootstrap resampling estimators for bias reduction in the situation in which linkage peaks at more than one QTL are of interest. METHODS: Bootstrap estimates were based on repeated sample splitting in the original dataset. We conducted simulation studies in nuclear families with 0 to 5 QTLs and applied the methods in a genome-wide analysis of a blood pressure phenotype in extended pedigrees from the Framingham Heart Study (FHS). RESULTS: Compared to naïve estimates in the original simulation samples, bootstrap estimates had reduced bias and smaller mean squared error. In the FHS pedigrees, the bootstrap yielded heritability estimates as much as 70% smaller than in the original sample. CONCLUSIONS: Because effect estimates obtained in an initial study are typically inflated relative to those expected in an independent replication study, successful replication will be more likely when sample size requirements are based on bias-reduced estimates.

Cardiovascular Diseases↗
PubMed2002

Sampling distribution of summary linkage disequilibrium measures.

The design of association studies is critically dependent upon the extent of linkage disequilibrium (LD) across different genomic regions, often summarised in terms of the mean absolute value of summary linkage disequilibrium measures. The two most commonly used measures are D' for estimating the magnitude or extent of LD, and Delta which is directly proportional to the power of LD mapping. We studied the sampling distribution of the mean of /D'/ and /Delta/ statistics for varying sample size and major allele frequencies. When the sample size is small or one allele frequency is extreme, estimates of the magnitude of association based on the mean of /D'/ can be substantially inflated. This inflation is more marked when the haplotype frequencies have been inferred from genotype counts. The net effect of this means that smaller studies will tend to show higher levels of LD. The magnitude of this inflation can be reduced by use of a bootstrap correction, and by avoiding using markers with extreme allele frequencies. In contrast, the /Delta/ statistic is much less affected by sample size and high major allele frequencies. These effects are illustrated with real data on 36 SNPs typed in an Ashkenasi Jewish population.

Humans↗
PubMed1995

Experimental design and efficient parameter estimation in preclinical pharmacokinetic studies.

Monte Carlo simulation technique used to evaluate the effect of the arrangement of concentrations on the efficiency of estimation of population pharmacokinetic parameters in the preclinical setting is described. Although the simulations were restricted to the one compartment model with intravenous bolus input, they provide the basis of discussing some structural aspects involved in designing a destructive ("quantic") preclinical population pharmacokinetic study with a fixed sample size as is usually the case in such studies. The efficiency of parameter estimation obtained with sampling strategies based on the three and four time point designs were evaluated in terms of the percent prediction error, design number, individual and joint confidence intervals coverage for parameter estimates approaches, and correlation analysis. The data sets contained random terms for both inter- and residual intra-animal variability. The results showed that the typical population parameter estimates for clearance and volume were efficiently (accurately and precisely) estimated for both designs, while interanimal variability (the only random effect parameter that could be estimated) was inefficiently (inaccurately and imprecisely) estimated with most sampling schedules of the two designs. The exact location of the third and fourth time point for the three and four time point designs, respectively, was not critical to the efficiency of overall estimation of all population parameters of the model. However, some individual population pharmacokinetic parameters were sensitive to the location of these times.

Animals↗
PubMed2003

Digital imaging as a possible approach in evaluation of islet yield.

Digital image analysis (DIA) is a new method in assessment of islet amount, which is expected to provide reliable and consistent results. We compared this method with conventional counting of small numbers of rat islets. Islets were isolated from 8 pancreases and counted in 24 samples in duplicate, first routinely by sizing according to estimated diameters under a calibrated reticule and then by processing of islets pictures taken by camera. As presumed, no significant difference was found in absolute numbers of islets per sample between DIA and conventional assessment. Volumes of islets per sample measured by DIA were on average more than 10% higher than amounts evaluated conventionally, which was statistically significant. DIA has been shown to be an important method to remove operator bias and provide consistent results. Evaluation of only two dimensions of three-dimensional objects still represents a certain limitation of this technique. With lowering of computer prices the system could become easily available for islet laboratories.

Animals↗
PubMed1996

How common is low back pain in the Nordic population? Data from a recent study on a middle-aged general Danish population and four surveys previously conducted in the Nordic countries.

STUDY DESIGN: Data were obtained in a Danish cross-sectional postal survey and compared with information from four methodologically similar studies conducted in some of the Nordic countries between 1977-1985. OBJECTIVES: The objectives were to estimate the lifetime cumulative incidence and the 1-year period prevalence of low back pain in the general population, to study whether there are any differences in the occurrence of low back pain according to age and sex, and to investigate whether low back pain is on the increase. SUMMARY OF BACKGROUND DATA: The prevalence of low back pain commonly is thought to be high, but estimates differ considerably between studies. It is also not known whether low back pain is more common in men or women or in certain age groups, and it is unclear whether the prevalence of low back pain has increased in the past years. METHODS: Prevalence estimates were established in a current study, and results then were adjusted to suit the age and sex criteria of four previous studies. RESULTS: Between 60-65% of 30- to 50-year-old men and women living in the Nordic countries reported at least one incident of low back pain during their lifetime, based on the information from four studies with a total sample size of 3513. The most likely 1-year period prevalence estimate is between 44-54%, based on two studies and a total sample of 2035 individuals. There was no consistent evidence favoring higher figures with increasing age or relating to any of the genders. No clearly observed time-related trend was noted. CONCLUSIONS: When data were examined from five methodologically similar studies on the 30- to 50-year-old Nordic population, there was reasonable consistency of prevalence figures. Thus, approximately 66% report having had low back pain at least sometime during their lifetime and approximately 50% sometime during the preceding year, with no significant differences relating to age or sex. The best method to investigate whether low back pain is on the increase might be through replicate studies.

Adult↗
PubMed2003

The risk of end stage liver disease and hepatocellular carcinoma among persons infected with hepatitis C virus: publication bias?

OBJECTIVES: In persons infected with hepatitis C virus (HCV), the incidence of cirrhosis and hepatocellular carcinoma (HCC) can be estimated by examining over time entire cohorts with known onset of HCV infection. We performed a systematic review of the literature to identify and to analyze studies that examine such cohorts. METHODS: A search of all articles from 1980 to 2001 was performed. Published studies were included in which chronic HCV infection was defined by elevation of liver enzymes or persistent RNA. We excluded studies in which cohorts were selected from patients with prevalent liver disease or in whom the onset of infection could not be estimated. Two investigators abstracted the data. The incidences of cirrhosis and HCC were analyzed in all studies and in categories based on study design, mode of HCV acquisition, sample size and duration of follow-up, age at the onset of infection, and the quality of estimating the onset of HCV infection. RESULTS: Of the articles, 21 fulfilled the selection criteria. Studies varied in sample size (17-1,680), duration of follow-up (8-45 yr), total person-years (157-34,098), and the mean age at onset of HCV (5-58 yr). The mean time to end stage liver disease (ESLD) was 4-23 yr and to HCC was 9-31 yr. A funnel plot showed a possible publication bias against studies with low incidence of ESLD and HCC. The pooled weighted incidence rates for ESLD and HCC based on infection mode were as follows: community-acquired HCV, 1.9 and 0 per 1,000 person-years; transfusion associated, 4.5 and 0.7; hemophilia patients, 7.9 and 1.0; anti-D IgG, 0.7 and 0 per 1,000 person-years. Poisson regression modeling showed that the incidence of ESLD is increased in studies with a low quality estimate of the onset of HCV infection, in community-acquired and transfusion-associated HCV, and in studies with prospective design. CONCLUSIONS: We found large variation in the incidence estimates of cirrhosis and HCC. Short duration of follow-up, small sample size, and possible publication bias may explain some of this variation. Low quality estimates of the onset of HCV infection, a prospective study design, and a transfusion- or hemophilia-related mode of acquisition were independent predictors of high reported incidence of ESLD.

Bias↗
PubMed2004

Mobile gene cassettes: a fundamental resource for bacterial evolution.

Horizontal gene transfer increases genetic diversity in prokaryotes to a degree not allowed by the limitations of reproduction by binary fission. The integron/gene cassette system is one of the most recently characterized examples of a system that facilitates horizontal gene transfer. This system, discovered in the context of multidrug resistance, is recognized in a clinical context for its role in allowing pathogens to adapt to the widespread use of antibiotics. Recent studies suggest that gene cassettes are common and encode functions relevant to many adaptive traits. To estimate the diversity of mobile cassettes in a natural environment, a molecular technique was developed to provide representative distributions of cassette populations at points within a sampling area. Subsequently, statistical methods analogous to those used for calculating species diversity were employed to assess the diversity of gene cassettes within the sample area in addition to gaining an estimate of cassette pool size. Results indicated that the number of cassettes within a 5x10-m sample area was large and that the overall mobile cassette metagenome was likely to be orders of magnitude larger again. Accordingly, gene cassettes appear to be capable of mobilizing a significant genetic resource and consequently have a substantial impact on bacterial adaptability.

Adaptation, Physiological↗
PubMed1980

The estimation of intraclass correlation in the analysis of family data.

The maximum likelihood estimator of the intraclass correlation coefficient rho in samples of unequal size from a multivariate normal distribution has been derived and compared to several other estimators, using Monte Carlo simulation. It is recommended that maximum likelihood be used if no prior knowledge concerning the value of rho is thought to be high. Fow low to moderate values of rho it is recommended that the analysis of variance estimator be used, with those families having only one member deleted from the analysis.

Analysis of Variance↗
PubMed2002

Atmospheric aerosol measurements of 238U and 232Th at Fernald, Ohio, and implications on inhalation dose calculations.

Measurements of the aerosol size distribution of 238U and 232Th at the U.S. Department of Energy's Fernald Environmental Management Project site were made to improve the inhalation dose calculations to off-site individuals. For approximately 1 y an 8-stage cascade impactor was co-located with a high volume sampler and operated at the Fernald Environmental Management Project site to collect aerosol samples. During most of the year, the site was dominated by giant particles with more than 70% of the mass of 238U above 15 microm. The seasonal average of the activity median aerodynamic diameter, based on the impactor samples, which excluded particles >15 microm, for both uranium and thorium was approximately 6.5 microm. These numbers reflect the activities at the site and the domination of the resuspension processes. During most sampling periods the size distribution was bimodal. Thorium concentrations were comparable to the uranium concentrations during the late spring and summer period and decreased to approximately 25% of the 238U concentration in the late summer. Fernald Environmental Management Project is required to calculate the maximum allowable dose from airborne emissions, excluding radon, to meet NESHAP compliance. These calculations assume an AMAD of 1 microm. We found that if you combine size distribution information with the latest ICRP 66 lung model you reduce the estimated dose by a factor of 7. Inclusion of the size distribution of radionuclides at any sampling site would substantially improve the dose estimates to the population.

Aerosols↗