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PubMed2001

Estimating risks in declining populations with poor data.

Census data on endangered species are often sparse, error-ridden, and confined to only a segment of the population. Estimating trends and extinction risks using this type of data presents numerous difficulties. In particular, the estimate of the variation in year-to-year transitions in population size (the "process error" caused by stochasticity in survivorship and fecundities) is confounded by the addition of high sampling error variation. In addition, the year-to-year variability in the segment of the population that is sampled may be quite different from the population variability that one is trying to estimate. The combined effect of severe sampling error and age- or stage-specific counts leads to severe biases in estimates of population-level parameters. I present an estimation method that circumvents the problem of age- or stage-specific counts and is markedly robust to severe sampling error. This method allows the estimation of environmental variation and population trends for extinction-risk analyses using corrupted census counts--a common type of data for endangered species that has hitherto been relatively unusable for these analyses.

Aging↗
PubMed1978

Comparative validity of random-interval and fixed-interval urinalysis schedules.

Accurate detection of unprescribed drug use by addicts in treatment may facilitate their rehabilitation. Many clinics collect urine samples at random, using fixed-interval collection schedules, which are not free from sampling error. Random-interval schedules minimize sampling error and consequently increase detectability of drug use by eliminating safe periods during which drug use cannot be detected. We compared these two methods by observing rates of detected opiate- and quinine-positive samples preceding and following implementation of random-interval schedules. Detected drug use doubled initially. As detection and clinical sanctions became more certain, drug use declined to well below its former level. Programs that use fixed-interval schedules may underdetect drug use by more than 50%. If patients can reliably predict safe periods, the possibility of using drugs without fear of detection may impede their rehabilitation.

Appointments and Schedules↗
PubMed1984

Intraductal carcinoma of the breast.

The management of intraductal carcinoma of the breast at the present time is necessarily diverse because there is difficulty in detecting it, as well as understanding its basic biology and natural history. Therapy has ranged from excisional biopsy with or without radiation to radical and extended radical mastectomy. The effects of radiation therapy upon these well-differentiated in situ lesions is undefined. The popularity of total mastectomy stems from a concern for the fate of breast tissue left in situ after removal of the focus of preinvasive carcinoma. Intraductal carcinoma of the breast has been shown to be a multicentric disease process in a large percentage of patients. Indeed, all breast tissue in these patients appears to be at risk for the eventual development of preinvasive and invasive carcinoma. However, the clinical significance of such residual foci of in situ carcinoma or ductal hyperplasia and dysplasia following resection of the breast, as in papillary carcinoma of the thyroid, is still open to question. Similar concern exists for a significant "sampling error" involved in biopsies of lesions of the breast: there were six instances of this in the present series (11 per cent). A "sampling error" of 6 per cent was found in a similar study of a group of patients with intraductal carcinoma. An error rate of 18 per cent was reported in another study. Again, the clinical significance of this "sampling error" remains open to question. The difficulty encountered in evaluating remaining breast tissue after a partial mastectomy has also been reason to consider total mastectomy in these patients. Residual or recurrent carcinoma in such altered breast tissue is difficult to diagnose at an early stage, either by physical examination or by the results of mammography. None of the patients in the present series had axillary nodal metastases and, theoretically, intraductal carcinoma should not be associated with axillary nodal metastasis. The small percentage of patients found to have invasive carcinoma following mastectomy for in situ carcinoma are likely to have minimally invasive lesions with, at most, a 23 per cent incidence of positive axillary nodes. The advantage gained by performing full axillary dissection or extensive nodal sampling in 60 per cent of the patients in this series, as well as in patients in other series, is difficult to ascertain without further study. The most logical choice of therapy would appear to be total mastectomy with limited axillary node sampling.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed2001

Screening and surveillance for complications related to gastroesophageal reflux disease.

Gastroesophageal reflux disease (GERD) and columnar-lined esophagus with intestinal metaplasia (Barrett's esophagus) are the major recognized risk factors for adenocarcinoma of the esophagus. The American College of Gastroenterology recommends that patients with long-standing GERD symptoms (particularly those 50 years of age or older) undergo endoscopic screening to identify Barrett's esophagus and that those patients who have Barrett's esophagus undergo regular endoscopic surveillance. These recommendations are made with the expectation that screening and surveillance will decrease mortality from esophageal cancer, although this association is unclear. Nonetheless, retrospective studies have shown that endoscopic surveillance can detect some early, curable neoplasms in patients with Barrett's esophagus. Dysplasia in Barrett's esophagus is widely regarded as the precursor of invasive malignancy. Although grading dysplastic changes is largely subjective, dysplasia remains the most appropriate biomarker for clinical evaluation of Barrett's esophagus. Flow-cytometric and p53 abnormalities may be earlier and more specific markers for cancer development, but application of these abnormalities is not yet recommended for clinical practice. Endoscopic surveillance also is adversely affected by biopsy sampling error. Techniques that may minimize biopsy sampling error include chromoendoscopy, endosonography, optical coherence tomography, and fluorescence detection techniques. Further studies are needed to clearly define the role of these techniques in surveillance, and none is practical for routine clinical use at this time. Although not specifically recommended, experimental ablative therapies, such as photodynamic therapy, can be considered by physicians for their patients with high-grade dysplasia in Barrett's esophagus, if they are provided as part of an established, approved research protocol.

Adenocarcinoma↗
PubMed2005

Sampling variability of liver biopsy in nonalcoholic fatty liver disease.

BACKGROUND & AIMS: In nonalcoholic fatty liver disease (NAFLD), the distinction between steatosis and steatohepatitis (NASH) and the assessment of the severity of the disease rely on liver histology alone. The aim of this study was to assess the sampling error of liver biopsy and its impact on the diagnosis and staging of NASH. METHODS: Fifty-one patients with NAFLD underwent percutaneous liver biopsy with 2 samples collected. The agreement between paired biopsy specimens was assessed by the percentage of discordant results and by the kappa reliability test. RESULTS: No features displayed high agreement; substantial agreement was only seen for steatosis grade; moderate agreement for hepatocyte ballooning and perisinusoidal fibrosis; fair agreement for Mallory bodies; acidophilic bodies and lobular inflammation displayed only slight agreement. Overall, the discordance rate for the presence of hepatocyte ballooning was 18%, and ballooning would have been missed in 24% of patients had only 1 biopsy been performed. The negative predictive value of a single biopsy for the diagnosis of NASH was at best 0.74. Discordance of 1 stage or more was 41%. Six of 17 patients with bridging fibrosis (35%) on 1 sample had only mild or no fibrosis on the other and therefore could have been under staged with only 1 biopsy. Intraobserver variability was systematically lower than sampling variability and therefore could not account for most of the sampling error. CONCLUSIONS: Histologic lesions of NASH are unevenly distributed throughout the liver parenchyma; therefore, sampling error of liver biopsy can result in substantial misdiagnosis and staging inaccuracies.

Adult↗
PubMed1987

The beta error and sample size determination in clinical trials in emergency medicine.

In the analysis of a clinical trial an investigator may fail to discern a statistically significant difference in outcome between control and experimental groups, when in fact one exists. Failure to demonstrate such a difference when it actually exists is known as "type II" error, and its probability of occurring is termed "beta." The purpose of our study was to determine the distribution of beta errors in negative trials in the Journal of the American College of Emergency Physicians (JACEP) (1972-1979) and Annals of Emergency Medicine (1980-1984). All negative comparative clinical trials appearing in JACEP and Annals from volume 1 (1972) to volume 13 (1984) were surveyed and were eligible for inclusion in the study. A trial was defined as negative if the investigator specifically stated that there was no significant difference in outcome between the experimental and control groups. For each negative trial the following parameters were calculated: beta error, based on the sample size used and the difference determined to be important to detect clinically; sample size required to detect a clinically meaningful difference as determined by the authors of this study; and minimum true difference that had to be detected in the trial at a beta equal to 0.20, to discern a statistically significant result. For the 13 years surveyed, we found 21 endpoints in 14 negative trials that were analyzable. Only one of the trials (7.1%) addressed the issues of beta errors and sample size determination. In the remaining 13 negative trials, the calculated beta error ranged from .60 to .97. For the endpoints analyzed, a sample size of up to 450 times larger than that used would have been required to detect a clinically important difference.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Trials as Topic↗
PubMed2004

A probabilistic expert system that provides automated mammographic-histologic correlation: initial experience.

OBJECTIVE: We sought to determine whether a probabilistic expert system can provide accurate automated imaging-histologic correlations to aid radiologists in assessing the concordance of mammographic findings with the results of imaging-guided breast biopsies. MATERIALS AND METHODS: We created a Bayesian network in which Breast Imaging Reporting and Data System (BI-RADS) descriptors are used to convey the level of suspicion of mammographic abnormalities. Our system is a computer model that links BI-RADS descriptors with diseases of the breast using probabilities derived from the literature. Mammographic findings are used to update pretest probabilities (prevalence of disease) into posttest probabilities applying Bayes' theorem. We evaluated the histologic results of 92 consecutive imaging-guided breast biopsies for concordance with the mammographic findings during radiology-pathology review sessions. First, radiologists with no knowledge of the biopsy results chose BI-RADS descriptors for the mammographic findings. After the histologic diagnosis was revealed, the radiologists assessed concordance between the pathologic results and the mammographic findings. We then input the information gathered from these sessions into the Bayesian network to produce an automated mammographic-histologic correlation. RESULTS: We had a sampling error rate of 1.1% (1/92 biopsies). Our expert system was able to integrate pathologic diagnoses and mammographic findings to obtain probabilities of sampling error, thereby enabling us to identify the incorrect pathologic diagnosis with 100% sensitivity while maintaining a specificity of 91%. CONCLUSION: Our probabilistic expert system has the potential to help radiologists in identifying breast biopsy results that are discordant with mammographic findings and discovering cases in which biopsy sampling errors may have occurred.

Adult↗
PubMedDate not supplied

Replication error-positive samples found in pheochromocytomas.

UNLABELLED: Adenomatous polyposis coli, (APC) and E-cadherin (CDH1) tumor suppressor genes were investigated in human pheochromocytoma. Both genes are components of adherens junctions, but are also involved in wnt signalling in which one of the target molecules is c-myc protein. MATERIALS AND METHODS: Fifteen sporadic pheochromocytomas were tested for gene instability by PCR/loss of heterozygosity. Detection of c-myc protein was performed using immunohistochemistry. RESULTS: One sample with allelic imbalance of the APC gene and one with allelic imbalance of the CDH1 gene were found. Interestingly, another type of genomic instability was detected--replication error-positive samples (RER+). Four out of 13 heterozygous samples were RER-positive (30.8%). The instability is the result of impaired cellular mismatch repair. Immunohistochemistry showed increased levels of c-myc in comparison to normal adrenal tissue. CONCLUSION: Our results suggest that microsatellite genetic instabilities of the E-cadherin gene have a role in pheochromocytoma development and progression. Detected instability indicates that mismatch repair may be targeted in pheochromocytoma. Increased expression of c-myc protein as well as allelic imbalances of APC and CDH 1 genes suggest that the wnt signalling pathway may have a role in this malignancy.

Adrenal Gland Neoplasms↗
PubMedDate not supplied

Statistical methods of computing reference values for side-to-side differences in nerve conduction studies.

This study uses theoretic derivations, statistical simulations, and empirical estimations to compare two ways of deriving reference values for side-to-side differences in nerve conduction parameters of healthy subjects. The two methods involve using the side-to-side differences (STSD) and the absolute values of the STSD (AVSTSD). The theoretic derivations showed that the population reference value of the AVSTSD is greater than the STSD reference values by 0.18%. Simulation studies showed that the AVSTSD yields greater sampling errors than the STSD method when establishing the reference values for nerve conduction parameters. However, the sampling variability is substantially reduced by using study samples of greater than 50, and the differences between the two methods in sampling errors are trivial as sample size approaches 100. Using H reflex (HR) and extensor digitorum brevis reflex (EDBR) clinical data, the two methods were compared. In contrast to the small theoretic differences in reference values, the AVSTSD method overestimated the reference value by 0.5 ms for the EDBR and 0.1 ms for the H reflex, when using data from a population sample, increasing the type II error (reducing sensitivity) for the EDBR. The STSD method is recommended for establishment of normal values and for clinical comparisons.

Electromyography↗
PubMed1988

A note on sampling variance estimates for Social Security program participants from the Survey of Income and Program Participation.

The Census Bureau's Survey of Income and Program Participation (SIPP) provides data that can be used to study the characteristics of Old-Age, Survivors, and Disability Insurance (OASDI) and Supplemental Security Income (SSI) program participants. It is important that estimates of sampling errors accompany such studies because the estimates may have large sampling errors due to the small number of sample cases available for specific analyses. The generalized sampling variances provided by the Census Bureau did not identify separately either program's participants and, therefore, do not pertain directly to analyses of these groups. This article describes an approach to the direct computation of sampling variances for OASDI and SSI program participants. The approach uses the pseudo stratum and half-sample codes available in SIPP public use data files. A table of generalized standard errors is constructed for participants of both programs aged 18 or older. Generalized standard errors could not be computed for child beneficiaries under age 18 because of a wide variation of design effects across subpopulation estimates.

Adolescent↗
PubMed2000

Comparison of forced-choice and subjective probability scales measuring behavioral intentions.

Three surveys compared the accuracy of predictions based on forced-choice and subjective probability scales. The latter produced significantly more accurate election predictions and significantly reduced the percentage of undecided, or "Don't Know" responses, compared to forced-choice scales in all three surveys. Analysis indicates subjective probability scales decrease sampling error and confirms there is an inherent source of error in traditional forced-choice questions about voting intentions not attributable to sampling error. The results are discussed with respect to (1) sampling and measurement errors in forced-choice and subjective probability scales measuring behavioral intentions, (2) their practical application, and (3) cognitive theory, especially support theory.

Adolescent↗
PubMed1995

Sources of variability in the human lymphocyte micronucleus assay: a population-based study.

The cytokinesis block method was used to examine the intraclass correlation coefficient of the human lymphocyte micronucleus assay, sources of variability, and practical issues regarding the number of samples per subject. Twenty samples of 100 binucleate cells from a single phlebotomy per subject were analyzed (n = 112), using methods to evaluate variance components. The results showed marked intraindividual (sampling error) variation greater than interindividual variation, and no between-group contribution to the total variance. The intraclass correlation was 41.6%, indicating that slightly greater than half of the total variation in micronucleus outcomes was due to error variance (i.e., 58.4%). After adjusting for age, the intraclass correlation coefficient decreased trivially from 41.6% to 39.8%. There was a strong differential gender effect, favoring a greater micronuclei frequency in women. In conclusion, the data suggest that most of the variability in our data set for the micronucleus assay was due to sampling error; a strong differential gender effect favoring females was also verified. Equally important, in terms of practical applications, our analysis of the appropriate number of samples per subject revealed that scoring greater than 1,000 cells (10 determinations per subject) yielded no substantial improvement in statistical sensitivity, compared to the traditional 20 determinations. We suggest that more attention should be directed toward improving the assay's utility, while reducing sampling error.

Age Factors↗
PubMed1976

Indium bone marrow scintigraphy as an aid in selecting marrow biopsy sites for the evaluation of marrow elements in patients with lymphoma.

One hundred and two previously treated lymphoma patients were studied with 111Indium bone marrow scans and bone marrow biopsies. The biopsies were considered to represent sampling errors when the cellularity of the biopsy did not reflect the general state of the marrow organ cellularity as demonstrated by the scan. In each instance the accuracy of the scan was confirmed by either another biopsy or the subsequent clinical course of the patient. Sampling errors were infrequent (1/51) in patients with normal peripheral blood counts and whose marrow had never been involved with tumor. Errors were especially likely (17/51) in patients who had had marrow involvement or those who had anemia, leukopenia, or thrombocytopenia. The 111Indium bone marrow scan allows the clinician to avoid selecting a biopsy site with a high risk for sampling error.

Adult↗
PubMed1993

A method for detecting variability arising from errors in sample processing of paraffin-embedded tissue for DNA content analysis.

We present a method for controlling variability that may arise from inconsistencies in sample preparation for DNA content analysis of paraffin-embedded tissue. Human tonsil tissue obtained from routine surgical specimens was embedded in paraffin according to standard protocols. Fifty-micrometer sections were cut from the block and analyzed each day for 20 days to establish control ranges. One tonsil tissue section was processed in parallel with each run of clinical specimens. In this context, a run was defined as the simultaneous processing of 50-microns tissue sections for extraction of cell nuclei (dewaxing and rehydrating). If the tonsil G0/G1 peak coefficient of variation (CV) exceeded 2 SDs of the established mean, and optimum instrument performance and staining were verified, all samples prepared with the tonsil control were reprocessed. Instrument performance and staining were assessed by using the appropriate external controls. By using this rejection rule (12s), the frequency of sample reprocessing in our laboratory was approximately 6%. When the run was repeated and the tonsil control CV was within acceptable range, the G0/G1 peak CV of the corresponding clinical specimens improved 25% of the time. Because most investigators are willing to accept higher CVs for paraffin-embedded tissue than for fresh tissue, it is desirable to have a control to detect decreased peak resolution, resulting from errors in sample processing.

Cell Nucleus↗
PubMed2000

Errors in histological grading by prostatic needle biopsy specimens: frequency and predisposing factors.

Sampling error is an inherent problem of prostate biopsy. Consequently, there are problems in determining whether a given carcinoma is clinically significant on the basis of biopsy results. This study assesses the factors that predispose to errors in biopsy grading, as well as the dimensions of sampling error due to these factors. Among 187 cases, biopsy grading error was retrospectively related to grade heterogeneity in the prostate and to biopsy-related factors. Clinically relevant biopsy grading errors occurred in a quarter of the cases. Of all grading errors, at least 17% resulted from misinterpretation by the pathologist only. Overall, prostates with grade heterogeneity revealed grading errors twice as frequently as specimens without grade heterogeneity. In most cases, however, grading error resulted from multiple factors, such as the number and length of cores obtained (p<0.05). This was an important finding because the mean core length was only 9.4 mm, whereas the biopsy needle is designed to obtain cores of 15 mm. Moreover, clinically relevant biopsy grading error had occurred in almost half of the cases when the Gleason score was based on a tumour deposit measvring less than 0.5 mm (p<0.05). The clinical consequences of these findings are important. Clinicians should try to obtain at least six biopsies, each 15 mm in length, to minimize grading error. Pathologists should be cautious in reporting Gleason scores based on tumour lesions smaller than 400x total magnification field. Interpretation could be refined, when necessary, by warning the urologist of the Limitations of the biopsy report.

Aged↗
PubMed2001

Stereotactic core-needle breast biopsy: a multi-institutional prospective trial.

PURPOSE: To assess the accuracy of stereotactic core-needle biopsy (CNB) of nonpalpable breast lesions within the context of clinically important parameters of anticipated tissue-sampling error and concordance with mammographic findings. MATERIALS AND METHODS: CNB was performed in 1,003 patients, with results validated at surgery or clinical and mammographic follow-up. Mammographic findings were scored according to the American College of Radiology Breast Imaging Reporting and Data System with a similar correlative scale for histopathologic samples obtained at either CNB or surgery. Agreement of CNB findings with surgical findings or evidence of no change during clinical and mammographic follow-up (median, 24 months) for benign lesions was used to determine results. Three forms of diagnostic discrimination measures (strict, working [strict conditioned by tissue sampling error], applied [working conditioned by concordance of imaging and CNB findings) were used to evaluate the correlation of CNB, surgical, and follow-up results. RESULTS: Strict, working, and applied sensitivities were 91% +/- 1.9; 92% +/- 1.8, and 98% +/- 0.9, respectively; strict, working, and applied specificities were 100%, 98% +/- 0.8, and 73% +/- 0.9; strict, working, and applied accuracies were 97%, 96%, and 79%. CONCLUSION: Percutaneous stereotactic CNB is an accurate method to establish a histopathologic diagnosis of nonpalpable breast lesions. Accuracy increases when additional surgery is performed for lesions with anticipated sampling error or when CNB findings are discordant with mammographic findings. An understanding of the interrelationship among these parameters is necessary to properly assess results.

Biopsy, Needle↗
PubMed2000

A survey of liver pathology in needle biopsies from HBsAg and anti-HBe positive individuals.

AIMS: To use laboratory data and liver biopsies, prospectively obtained from hepatitis B surface antigen (HBsAg) and anti hepatitis B e antigen (anti-HBe) positive patients, for the assessment of: (1) the relation between biopsy length/number of portal tracts and sampling error; (2) the relation between the severity of piecemeal necrosis and the new grading terminology (minimal, mild, moderate, and severe chronic hepatitis); and (3) liver pathology, which has not been studied in patients with this specific serological profile. METHODS: The study group (n = 174) included 104 patients with normal aminotransferase concentrations and no cases with clinically apparent cirrhosis. The specimen length and number of portal tracts were measured at light microscopy examination. Sampling error analysis was related to the discrepancies between aminotransferase concentrations versus histological grade. Detailed histological scorings were undertaken by the reference pathologist and compared with laboratory and hepatitis B virus (HBV) DNA precore sequence data. RESULTS: Sampling error seemed to be a constant feature, even for biopsies > or = 20 mm, but increased dramatically in biopsies < 5 mm long and/or containing less than four portal tracts. Between 25% and 30% of biopsies, graded as "mild" or "moderate" activity showed features of moderate and severe piecemeal necrosis, respectively. Ten per cent of the patients with normal aminotransferase values had stage III-IV hepatic fibrosis, and 20% had piecemeal necrosis. Only cytoplasmic, not nuclear, core antigen expression was a strong predictor of high hepatitis B viraemia. There was no association between precore stop codon mutations, grade/stage of liver disease, and hepatitis B core antigen (HBcAg) expression. CONCLUSIONS: The specimen available for light microscopical examination should be > 5 mm long and should contain more than four portal tracts. In addition, the new grading terminology might give the clinician an inappropriately mild impression of the severity of piecemeal necrosis. Furthermore, even in the presence of normal aminotransferase concentrations, considerable liver pathology can be found in 10-20% of HBsAg and anti-HBe positive individuals; such pathology is not associated with the occurrence of precore stop codon mutations.

Biopsy, Needle↗