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PubMed1986

Data collection organization effect in the National Medical Care Utilization and Expenditure Survey.

The National Medical Care Utilization and Expenditure Survey (NMCUES), which has a complex survey design, was further complicated by combining two independently drawn national samples of households from the Research Triangle Institute (RTI) and the National Opinion Research Center (NORC). It is assumed that because the structures of both national area samples are similar, they are thereby compatible and allow for the derivation of unbiased national estimates of relevant health parameters. However, even though the two survey organizations operate under a common set of survey conditions with comparable samples, the actual data generated may differ across them, over and above differences due to pure sampling error. The NORC sample had a higher representation of individuals living in non-SMSA urban areas, of individuals with fair or poor health status, and of individuals incapable of performing usual activity. In addition, significantly higher mean estimates of the number of restricted activity days, of total charges for dental visits, for non-doctor visits and for hospital stays, and of overall total charges, characterized the NORC sample. The consistent directional difference in these health care estimates indicated a data collection organization effect was operational in the NMCUES. A comparison of item nonresponse rates, however, indicated the level of data quality on this dimension was generally equivalent across survey organizations. Further, the observed survey design differentials across organizations did not significantly differ in their impact on the precision in survey estimates. When a data collection organization effect is operational for a set of related survey statistics, as in the National Medical Care Utilization and Expenditure Survey, the use of more than one survey organization should be seriously considered.

Catchment Area, Health↗
PubMed2005

Continuous monitoring in sewer networks an approach for quantification of pollution loads from CSOs into surface water bodies.

Different approaches for quantification of pollution loads discharged from combined sewer networks into surface water bodies have been observed over the last few years and decades, but a large number of unresolved problems still remain. Many monitoring campaigns have been based on manual or automated spot sampling - with the long known limitations of this method such as sampling errors and errors due to sample conservation, transport and preparation. On the other hand, only recently have sensors became available which are suitable for continuous application in sewer networks. A large number of practical problems still have to be solved before continuous monitoring in sewer networks will be successful. Additionally, most of the applicable sensors are based on surrogate methods which results in a considerable effort for reference measurements for sensor calibration. Finally, it has to be considered that, depending on the sewer network topography, deposition and remobilisation of pollutants varies considerably, which limits the generality of monitoring results and, subsequently, their applicability as a base for the design of storm water tanks or combined sewer overflows (CSO). A monitoring station for continuous monitoring of load discharges from a CSO has been installed and operated for more than one year. The design and equipment of the measurement station, operational experiences and results are given in this paper.

Calibration↗
PubMed1990

Hematologic response to acute inflammation: the band neutrophil revisited.

The value of the routine visual (manual) 100-cell differential leukocyte count (DLC) as a screening test in asymptomatic individuals or in patients on admission without suspected distributional or morphologic abnormalities has been challenged in the medical literature. More recently, the usefulness of an increase in the band neutrophils or a "left-shift" in the manual DLC has also been in question. This article discusses the largest sources of error in the routine DLC, namely, cell-identification errors, distributional errors, and statistical sampling errors. The latest flow cytometric, cytochemical, automated leukocyte differential counters offer a viable, reliable alternative to the highly imprecise 100-cell DLC. Studies have shown that these newer instruments are sensitive in detecting the hematologic response to acute inflammation or infection and have the advantage of vastly increased precision and therefore of improved reliability of the differential leukocyte count.

Acute Disease↗
PubMed1981

Measuring error and sampling variation in stereology: comparison of the efficiency of various methods for planar image analysis.

An evaluation is made of the relative efficiency (precision of the final estimate per unit time of measurement on a given set of sections) of different methods for planar analysis aimed at estimating aggregate, overall stereological parameters (such as VV, SV). The methods tested are point-counting with different densities of test points (4 less than or equal to PT less than 900 per picture), semiautomatic computer image analysis with MOP and automatic image analysis with Quantimet, for obtaining VV and SV estimates. One biological sample as well as three synthetic model structures with known coefficients of variation between sections are used. The standard error of an estimate is mainly determined by the coefficient of variation between sampling units (= sections in the present paper) so that measuring each sample unit with a very high precision is not necessary. Automatic image analysis and point-counting with a 100-point grid were the most efficient methods for reducing the relative standard errors of the VV and SV estimates to equivalent levels in the synthetic models. Using a 64-point grid was as precise, and about 11 times faster than using a tracing device for obtaining the estimate of VV in the biological sample.

Animals↗
PubMed2004

Comparative methods based on species mean values.

Comparative methods that use simple linear regression based on species mean values introduce three difficulties with respect to the standard regression model. First, species values may not be independent because they form part of a hierarchically structured phylogeny. Second, variation about the regression line includes two sources of error: 'biological error' due to deviations of the true species mean values from the regression line and sampling error associated with the estimation of these mean values [B. Riska, Am. Natural. 138 (1991) 283]. Third, sampling error in the independent variable results in an attenuated estimate of the regression slope. We consider estimation and hypothesis testing using two statistical models which explicitly justify the use of the species mean values, without the need to account for phylogenetic relationships. The first (random-effects) is based on an evolutionary model whereby species evolve to fill a bivariate normal niche space, and the second (fixed-effects) is concerned with describing a relationship among the particular species included in a study, where the only source of error is in the estimation of species mean values. We use a modification of the maximum-likelihood method to obtain an unbiased estimate of the regression slope. For three real datasets we find a close correspondence between this slope and that obtained by simply regressing the species mean values on each other. In the random effects model, the P-value also approximates that based on the regression of species mean values. In the fixed effects model, the P-value is typically much lower. Simulated examples illustrate that the maximum-likelihood approach is useful when the accuracy in estimating the species mean values is low, but the traditional method based on a regression of the species mean values may often be justified provided that the evolutionary model can be justified.

Acer↗
PubMed1994

Comparison of liquid and dried blood for neonatal hemoglobinopathy screening: laboratory and programmatic issues.

OBJECTIVES: To compare laboratory and programmatic issues in neonatal hemoglobin screening in two systems using either liquid cord blood or heel puncture blood dried on filter paper (DB) to determine the accuracy of hemoglobin phenotype; the collection rate of cord blood versus DB; and the types of and reasons for errors. METHODS: Cord blood samples for 6904 newborns were analyzed by electrophoresis in a large hospital laboratory. DB samples on the same cohort were analyzed by isoelectric focusing in a state public health laboratory. RESULTS: Interlaboratory concordance was 99.4% for 6904 matched specimen pairs, which included 27 disease and 596 carrier phenotypes. In 42 pairs, discordances for potential disease phenotypes occurred with cord blood samples. Errors involving carrier phenotypes occurred in 15 cord blood samples and 14 DB samples. Inconclusive results requiring repeat testing occurred more often in the cord blood testing system (92) than in the DB system (23). Clerical transcriptions and limitations of the techniques accounted for most laboratory errors. Noncompliance in sample collection occurred more frequently with cord blood (181) than DB (86). CONCLUSIONS: Both systems are subject to errors, but are equally reliable for neonatal hemoglobinopathy screening.

Blood Protein Electrophoresis↗
PubMed1993

Sampling variance estimates for SSA program recipients from the 1990 Survey of Income and Program Participation.

Since 1987 the Social Security Administration (SSA) has published a special set of tabulations on SSA program recipients in the Annual Statistical Supplement to the Social Security Bulletin using data derived from the Census Bureau's Survey of Income and Program Participation (SIPP). Estimates of sampling errors pertaining to these tabulations were derived from the 1984 SIPP panel. This article provides updated sampling error estimates for the 1990 SIPP panel to be used in conjunction with the SIPP-based tabulations provided in the Annual Statistical Supplement for 1992 and 1993. The computational approach is essentially the same as that used in the earlier analysis. Sampling variances are estimated by half-sample replication using the pseudo stratum and half-sample codes available on SIPP public use data files. Generalized tables of standard errors are provided for all SSA program participants. An appendix provides detailed specifications about the calculations. In order that it be self-contained, this article repeats much of the methodological exposition in the previous article that appeared in the October 1988 issue of the Social Security Bulletin.

Adolescent↗
PubMed1993

Ductal carcinoma of breast: nuclear grade as a predictor of S-phase fraction.

Nuclear grade (NG) and S-phase fraction (SPF) are established independent prognostic variables for ductal breast carcinomas. Nuclear grade can be assigned by a pathologist in a simple fashion during histopathologic evaluation of the tumor, while SPF requires flow cytometric evaluation of tumor samples. This prospective study was undertaken to determine whether elevated SPF could be predicted from NG alone and how NG and SPF correlate with c-erbB-2 expression. Eighty-two breast carcinomas of ductal type were assigned an NG of low (grade 1 or grade 2) or high (grade 3). S-phase fraction was recorded initially from fresh-frozen tissue samples and was designated as either low SPF (below the value designated as the cutoff for elevated SPF) or high SPF (a value at or greater than the cutoff value). On fresh tissue the NG predicted the range of SPF (low or high) in 89% of cases. Four percent of the cases that did not correlate could definitely be attributed to sample error. The remaining 7% that did not correlate could have been due to sample error, specimen quality, or tumor heterogeneity, as demonstrated by reversal of SPF range as performed on paraffin blocks of tumor. Eighty-eight percent of the tumors positive for c-erbB-2 were NG 3 and 12% were NG 2. All c-erbB-2 tumors were aneuploid. This study demonstrates the importance of carefully assigning NGs on tissue and indicates the importance of reviewing flow cytometric data side by side with histopathologic parameters to detect discrepancies between these two modalities. Careful nuclear grading assignment can accurately predict the range of SPF.

Breast Neoplasms↗
PubMed1995

The effect of reducing the number of cells scored on the performance of the in vivo rat liver UDS assay.

The most labour-intensive feature of the in vivo rat liver UDS assay is the scoring of hepatocyte autoradiograms by microscope. Even with image analyser and computer equipment the scoring phase of a full study might require half of the technical effort applied. Practice recommended by guidelines has been to score 50 cells/slide and two slides per animal. Now sufficient data have been accumulated, an evaluation was made to observe whether this procedure was necessary. An analysis of the accumulated UDS database in our laboratory was made to determine the sources of variability of mean net nuclear grain count, [N-C]. It was observed that the two largest components of variation in negative control animal mean [N-C] were between-day and interanimal variability. The contribution from sampling error during slide scoring was relatively small. Theoretical calculations showed that the greater sampling error derived from scoring 30 rather than 50 cells/slide would result in only a marginal increase in total assay variation. To test this, 30 cells/slide were randomly selected from the 50 cells scored originally in negative control animals in each of 18 studies over an 18-month period. It was confirmed that reducing the number of cells had a negligible effect on the variation of negative control animal mean [N-C] values. Furthermore, analysis of data from 10 more studies confirmed that within-study variation would be essentially unaffected by scoring 30 cells/slide. The use of 30 rather than 50 cells per slide (a total of 60 cells per animal) has therefore been adopted for all current studies and scoring procedures modified to avoid operator bias during the selection of a smaller number of cells.

Animals↗
PubMedDate not supplied

Barrett esophagus: endoscopic findings and what to biopsy.

Barrett esophagus (BE) is considered the precursor for nearly all cases of esophageal adenocarcinoma. The potential sequence from intestinal metaplasia to dysplasia to cancer can best be monitored by careful endoscopic observation and surveillance biopsies. The ability to diagnose BE, biopsy accurately, and appropriately monitor are requisites for all who care for patients with this disorder. The normal endoscopic anatomy of the esophagogastric junction region and the changes that are associated with BE are discussed. The relationship of the squamocolumnar mucosal junction to the proximal margin of the gastric folds and the distal extent of the linear esophageal vessels is the principal landmark for diagnosis. Chromoendoscopy with methylene blue and Lugol iodine will enhance endoscopic observation, thereby allowing directed biopsies. Biopsy forceps and technique are reviewed along with the when and where for surveillance biopsies. Since most dysplasia and intramucosal cancer is focal and invisible to the endoscopist, it is easy to understand why the sampling error exceeds 95% using a standard four-quadrant biopsy protocol. Currently, this sampling error can be reduced by four-quadrant biopsies at closer intervals and biopsies of even the most minor focal abnormalities of mucosa in the BE segment. Screening may be enhanced in the future depending upon successful development of new cytologic, spectrographic, and tomographic methods capable of identifying foci of dysplasia or cancer that can be confirmed by targeted biopsies.

Adenocarcinoma↗
PubMed2006

National Survey of Family Growth, Cycle 6: sample design, weighting, imputation, and variance estimation.

OBJECTIVES: Cycle 6 of the National Survey of Family Growth (NSFG) was conducted by the National Center for Health Statistics in 2002 and early 2003. This report describes how the sample was designed, shows response rates for various subgroups of men and women, describes how the sample weights were computed to make national estimates possible, shows how missing data were imputed for a limited set of key variables, and describes the proper ways to estimate sampling errors from the NSFG. The report includes both nontechnical summaries for readers who need only general information and more technical detail for readers who need an in-depth understanding of these topics. METHODS: The NSFG Cycle 6 was based on an independent, national probability sample of men and women 15-44 years of age. It was the first NSFG ever to include a national sample of men 15-44 as well as a sample of women. Fieldwork was carried out by the University of Michigan's Institute for Social Research (ISR) under a contract with NCHS. In-person, face-to-face interviews were conducted by professional female interviewers using laptop computers. In all, 12,571 women and men-7,643 females and 4,928 males-were interviewed, the largest NSFG ever done. RESULTS: Analysis of NSFG Cycle 6 data requires the use of sampling weights and estimation of sampling errors that accounts for the complex sample design and estimation features of the survey. Examples of how to use several available software packages that incorporate complex design features in estimation, such as SAS, SUDAAN, and STATA, are presented.

Adolescent↗
PubMed1996

Incidence of extramural venous invasion in colorectal carcinoma: findings with a new technique.

In reported studies of extramural venous invasion (EVI) by colorectal carcinoma (CRC) in which conventional preparations involving a sectioning plane perpendicular to the tumor were used, an incidence as high as 36% has been found for unselected surgical material from patients operated on for cure. However, with this preparation technique, not all of the veins that exit the bowel wall roughly at right angles can be examined adequately. We investigated whether preparation of the adjacent vascular connective tissue with tangential sectioning might not result in different EVI rates. A total of 100 unselected surgical specimens of the bowel bearing 103 CRCs were prepared using a previously undescribed method, and EVI was found in 54.1% of the cases considered to have been treated curatively. To assess EVI fully, a complete study of all the vessels draining the tumor would be required yet the conventional preparation technique is associated with the distinct possibility of sampling error, because only a few vessels in each block are sectioned in the longitudinal axis. This sampling error might well be the explanation for the considerably higher incidence of EVI in our cases than in the reports in the literature. In all patients with EVI, the possibility of hematogenous metastases exists, and this has a significant bearing on the question of selecting patients for adjuvant chemotherapy.

Carcinoma↗
PubMed1999

Estimating noncancer uncertainty factors: are ratios NOAELs informative?

The prominent role of animal bioassay evidence in environmental regulatory decisions compels a careful characterization of extrapolation uncertainties. In noncancer risk assessment, uncertainty factors are incorporated to account for each of several extrapolations required to convert a bioassay outcome into a putative subthreshold dose for humans. Measures of relative toxicity taken between different dosing regimens, different endpoints, or different species serve as a reference for establishing the uncertainty factors. Ratios of no observed adverse effect levels (NOAELs) have been used for this purpose; statistical summaries of such ratios across sets of chemicals are widely used to guide the setting of uncertainty factors. Given the poor statistical properties of NOAELs, the informativeness of these summary statistics is open to question. To evaluate this, we develop an approach to "calibrate" the ability of NOAEL ratios to reveal true properties of a specified distribution for relative toxicity. A priority of this analysis is to account for dependencies of NOAEL ratios on experimental design and other exogenous factors. Our analysis of NOAEL ratio summary statistics finds (1) that such dependencies are complex and produce pronounced systematic errors and (2) that sampling error associated with typical sample sizes (50 chemicals) is nonnegligible. These uncertainties strongly suggest that NOAEL ratio summary statistics cannot be taken at face value; conclusions based on such ratios reported in well over a dozen published papers should be reconsidered.

Algorithms↗
PubMed1995

Comparative analysis of human papillomavirus detection by PCR and non-isotopic in situ hybridisation.

AIMS--To assess the relative diagnostic performance of the polymerase chain reaction (PCR) and non-isotopic in situ hybridisation (NISH) and to correlate these data with cytopathological assessment. METHODS--Paired analysis of human papillomavirus (HPV) detection was performed by PCR and NISH on exfoliated cervical cells from 122 women attending a routine gynaecological examination. PCR amplification followed by generic and HPV type specific hybridisation was compared with NISH on a parallel cervical smear. RESULTS--Overall, 32 cases were positive by NISH and 61 positive by PCR. Of the 105 cases in which both PCR and NISH were interpretable, 76 (26%) were normal smears, 20 of which were HPV positive by NISH and 37 (49%) by PCR. Of 17 borderline smears, two were NISH positive and 12 PCR positive. Eight of nine smears containing koilocytes were positive by NISH and seven by PCR. Of three dyskaryotic smears, none were NISH and two were PCR positive. The concordance of NISH and PCR in these samples was 57%. To assess sampling error, NISH and PCR were performed on an additional 50 cases using aliquots from the same sample. This increased the concordance between assays to 74%. Filter hybridisation of PCR products with the cocktail of probes used in NISH (under low and high stringency conditions) demonstrated that several cases of NISH positivity could be accounted for by cross-hybridisation to HPV types identified by PCR but not present in the NISH probe cocktail. CONCLUSIONS--Sampling error and potential cross-hybridisation of probe and target should be considered in interpretation of these techniques. PCR is more sensitive because it provides for the amplification of target DNA sequences. In addition, the PCR assay utilised in this study detects a wider range of HPV types than are contained in the cocktails used for NISH. However, PCR assays detect viral DNA present both within cells and in cervical fluid whereas NISH permits morphological localisation.

Cervix Uteri↗
PubMed1990

Stereotactic fine-needle aspiration for cytologic diagnosis of nonpalpable breast lesions.

Fine-needle aspiration for cytologic diagnosis was performed on 219 nonpalpable breast lesions by using a stereotactic localization technique. Cytologic results were correlated with mammographic findings, and therapeutic decisions were based on the results of both procedures. Representative cytologic material was obtained in 74% of the lesions. Strict criteria of representativeness were observed. If only cases with representative cytologic yield are considered, the sensitivity was 93% and the specificity was 97%. The predictive values were high except for the predictive value of a negative cytologic finding in a spiculated lesion (50%). Sampling errors caused by abundant fibrosis, needle deviation, and difficulty in defining the lesion on the stereoscopic views are discussed. Another source of sampling error may be the mixed nature of some lesions consisting of benign and malignant components. Fine-needle aspiration of 219 nonpalpable breast lesions by using a stereotactic localization device yielded representative cytologic samples in 74% of the lesions.

Biopsy, Needle↗
PubMed2004

Colonic neoplastic polyps: biopsy is not efficient to exclude malignancy. The Trafford experience.

The biological behaviour of the polyp depends entirely on its histological subtype. Adenomas are the classic precursors to carcinoma. Polyp biopsy can differentiate neoplastic (adenoma and carcinoma) from non-neoplastic polyps (hyperplastic, inflammatory, hamartomatous). Due to potential sampling error, biopsy does not always differentiate between adenoma and carcinoma. Our aim was to investigate the degree of this potential sampling error. We carried out a study to compare the results of biopsies vs. total tissue examinations in a cohort of 433 neoplastic polyps. In this study 18.5% of carcinomatous polyps show definitive malignant elements only when the entire polyp is presented to the pathologist. We have therefore adopted a special reporting template if the polypoidal tumour is either biopsied or incompletely excised. The study also showed that within adenomas there could be variance of architectural patterns between the biopsy and the whole specimen. In this series, biopsying malignant colonic polyps gives rise to 18.5% false negative results and therefore it is significantly less efficient in the diagnosis of malignancy compared to total polyp examination.

Adenoma↗
PubMed2000

Method to resolve microphone and sample location errors in the two-microphone duct measurement method

Utilizing the two-microphone impedance tube method, the normal incidence acoustic absorption and acoustic impedance can be measured for a given sample. This method relies on the measured transfer function between two microphones, and the knowledge of their precise location relative to each other and the sample material. In this article, a method is proposed to accurately determine these locations. A third sensor is added at the end of the tube to simplify the measurement. First, a justification and investigation of the method is presented. Second, reference terminations are measured to evaluate the accuracy of the apparatus. Finally, comparisons are made between the new method and current methods for determining these distances and the variations are discussed. From this, conclusions are drawn with regards to the applicability and need for the new method and under which circumstances it is applicable. Results show that the method provides a reliable determination of both microphone locations, which is not possible using the current techniques. Errors due to inaccurate determinination of these parameters between methods were on the order of 3% for R and 12% for Re Z.

Journal Article↗
PubMed2003

Yield of endoscopic ultrasound-guided fine-needle aspiration biopsy in patients with suspected pancreatic carcinoma.

BACKGROUND: Although atypical or suspicious cytology may support a clinical diagnosis of a malignancy, it is often not sufficient for the implementation of therapy in patients with pancreatic carcinoma. Endoscopic ultrasound-guided fine-needle aspiration biopsy (EUS-FNAB) is a relatively new method for obtaining cytology samples, and one that may decrease the number of atypical/suspicious diagnoses. The goals of the current study were to prospectively evaluate the yield of EUS-FNAB in the diagnosis of patients presenting with solid pancreatic lesions and to evaluate the significance of atypical, suspicious, and false-negative aspirates. METHODS: All patients who presented with a solid pancreatic lesion and underwent EUS-FNAB over a 13-month period were included in the current study. One endoscopist performed all EUS-FNABs. On-site evaluation of specimen adequacy by a cytopathologist was available for each case. Follow-up included histologic correlation (n = 21) and clinical and/or imaging follow-up (n = 80), including 38 patients who died of the disease. RESULTS: EUS-FNABs were obtained from 101 patients (mean age, 62 +/- 11.8 years; age range, 34-89 years). The male-to-female ratio was 2:1. Sixty-five percent of the lesions were located in the head of the pancreas, 12% were located in the uncinate, 17% were located in the body, and 6% were located in the tail. The mean size of the tumors was 3.3 cm (range, 1.3-7 cm). A median of 4 needle passes were performed (range, 1-11 needle passes). Sixty-two biopsies (61.4%) were interpreted as malignant on cytologic evaluation, 5 (5%) as suspicious for a malignancy, 6 (5.9%) as atypical/indeterminate, and 26 (25.7%) as benign processes. Of the 76 malignant lesions, 71 were adenocarcinomas, 3 were neuroendocrine tumors, 1 was a lymphoma, and 1 was a metastatic renal cell carcinoma. All except one of the suspicious/atypical aspirates were subsequently confirmed to be malignant. Agreement was complete for the atypical cases. Among the suspicious cases, 2 of the 5 were identified as carcinoma by one cytopathologist and as suspicious lesions by the other, yielding a 40% disagreement rate between the 2 cytopathologists. Therefore, for the 10 atypical or suspicious cases that later were confirmed to be malignant, the final diagnosis of malignant disease was not made due to scant cellularity that could be attributed to sampling error in 8 cases and to interpretative disagreement in 2 cases (20%). All four false-negative diagnoses were attributed to sampling error. Two percent of all biopsies were inadequate for interpretation. Of the 99 adequate specimens, 72 yielded true-positive results, 23 yielded true-negative results, and 4 yielded false-negative results. No false-positives were encountered. Therefore, the sensitivity, specificity, positive predictive value, and negative predictive value of EUS-FNAB for solid pancreatic masses were 94.7% (95% confidence interval [CI], 89.7-99.8%), 100%, 100%, and 85.2% (95% CI, 71.8-98.6%), respectively. CONCLUSIONS: EUS-FNAB is a safe and highly accurate method for tissue diagnosis of patients with solid pancreatic lesions. Patients with suspicious and atypical EUS-FNAB aspirates deserve further clinical evaluation.

Adult↗