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PubMed1992

Perimetric follow-up in glaucoma with a reduced set of test points.

The global mean defect (GM) is probably the most useful visual field index for glaucoma follow-up. We compared 50 regional subsets of test locations to estimate the GM. Using the data on 424 automated fields of 257 patients with either primary open-angle glaucoma or ocular hypertension, we calculated the partial sample error of the regional mean defect as compared with the GM. In many regions, the measured sample error was greater than expected for a representative sample of points. Some sample errors were up to 5 times larger (regions "upper hemifield" and "lower hemifield"). Only a few subsets proved to be representative of the whole field, namely, regions "ring 3" (10 degrees-15 degrees), "ring 4" (15 degrees-20 degrees) and "ring 5" (20 degrees-25 degrees). The use of such programs for follow-up is very accurate for staging. Moreover, theoretical calculations reveal that trend analysis is even more significant if the reduction in examination time is combined with a proportional increase in examination frequency.

Adolescent↗
PubMed1992

Estimates from two survey designs: national hospital discharge survey.

The methodology for the National Hospital Discharge Survey (NHDS) has been revised in several ways. These revisions, which were implemented for the 1988 NHDS, included adoption of a different hospital sampling frame, changes in the sampling design (in particular the implementation of a three-stage design), increased use of data purchased from abstracting service organizations, and adjustments to the estimation procedures used to derive the national estimates. To investigate the effects of these revisions on the estimates of hospital use from the NHDS, data were collected from January through March of 1988 using both the old and the new survey methods. This study compared estimates based on the old and the new survey methods for a variety of hospital and patient characteristics. Although few estimates were identical across survey methodologies, most of the variations could be attributed to sampling error. Estimates from two different samples of the same population would be expected to vary by chance even if precisely the same methods were used to collect and process the data. Because probability samples were used for the old and new survey methodologies, sampling error could be measured. Approximate relative standard errors were calculated for the estimates using the old and new survey methods. Taking these errors into account, less than 10 percent of the estimates were found to differ across survey methodologies at the 0.05 level of significance. Because a large number of comparisons were made, 5 percent of the estimates could have been found to be significantly different by chance alone. When there were statistically significant differences in nonmedical data, the new methods appeared to produce more accurate estimates than the old methods did. Race was more likely to be reported using the new methods. "New" estimates for hospitals in the West Region and government-owned hospitals were more similar than the corresponding "old" estimates to data from the census of hospitals conducted by the American Hospital Association. The numerous significant differences in estimates for bed size categories between the two survey methodologies reflected the change in the universe and definition of beds for the new survey. Few statistically significant differences were found in the medical data using the old and the new survey methods. Two main differences, in estimates for cataract and alcohol dependence syndrome, may have resulted from problems with the new survey. A measurement error, reporting outpatients to the NHDS, is one possible explanation of the higher estimates for diagnosis of cataract using the new survey methods.(ABSTRACT TRUNCATED AT 400 WORDS)

Bias↗
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↗
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↗
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↗
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↗
PubMed1990

Flow cytometric DNA ploidy analysis of soft tissue sarcomas. A comparative study of preoperative fine needle aspirates and postoperative fresh tissues and archival material.

Flow cytometric (FCM) DNA ploidy measurements on frozen fresh samples of soft tissue sarcomas were compared with the corresponding analyses on preoperative fine needle aspirates and postoperative formalin-fixed archival tissues from the same tumors. A concordance in ploidy status (diploid versus non-diploid) was obtained for 63% of the fresh tissue-fine needle aspiration (FNA) sample comparisons and for 85% of the fresh tissue-archival material comparisons. The majority of discordances in the fresh tissue-FNA sample comparisons could be explained by FNA sampling errors. In the remaining discordant cases (3 of 27 FNA sample comparisons and 6 of 40 archival material comparisons), sampling errors could not explain the differences in ploidy status. The discordant cases were evenly distributed among the different sampling methods. Method reproducibility was not responsible for the differences in ploidy determinations; tumor heterogeneity may be an explanation for the discrepancies. This study showed that archival soft tissue sarcoma samples are as well suited for DNA ploidy analysis as are fresh frozen tissues.

Archives↗
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↗
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↗
PubMed1978

Operative biopsy of the pancreas using the Trucut needle.

The results of 14 operative biopsies of the pancreas using the Trucut technique are presented. There was no significant complication attributable to the biopsy, and in all cases an adequate tissue specimen was obtained, facilitating either frozen or paraffin section histological diagnosis. One false negative result was obtained which was due to sampling error. This technique is recommended as a good alternative when operative pancreatic biopsy is required. It is technically simple, has an acceptably low sampling error, provides a good tissue specimen for histological examination, and has few complications.

Adenocarcinoma↗
PubMed1985

The clinical use of radionuclide bone marrow imaging.

Bone marrow aspiration and biopsy are excellent techniques for evaluating bone marrow, but this evaluation is limited to a small part of the total blood-forming organ. With the introduction of radionuclide bone marrow imaging, a simple technique became available that overcomes marrow sampling errors by giving a total body view of functioning marrow. Furthermore, the procedure is noninvasive and provides an atraumatic method for evaluating a number of clinical problems including a discrepancy between bone marrow histology and clinical status (possible marrow sampling error), the determination of amount of active marrow after radiation and chemotherapy when further therapy is being considered, detection of sites of extramedullary hematopoiesis, location of the optimal sites for bone marrow biopsy, the diagnosis and staging of diffuse hematologic disorders, detection of metastases, the diagnosis of bone marrow infarcts in hemolytic anemias, and detecting avascular necrosis of the femoral heads. There are two major classes of bone marrow agents: (1) those that are incorporated into the erythroid precursors such as radioiron and (2) colloids that are taken up by the reticuloendothelial system (RES). Indium-111 chloride was originally considered to be an erythropoietic agent but appears to share some properties of RES labels. The best label to use is dependent on the disease being evaluated.

Anemia, Aplastic↗
PubMed1990

Cytophotometry in tumor pathology. A critical review of methods and applications, and some results of DNA analysis.

In tumor pathology the quantitation of cellular substances can be of diagnostic value. Microscope cytophotometry and digital image analysis and, on the other hand, flow cytometry are supplementary methods for measuring, each with a typical spectrum of application. The methods are predominantly used for DNA analysis: Static and image cytophotometry are applicable to cytologic and histologic slides preferably for identifying stem lines in tumors of heterogenous morphology and in merely circumscribed lesions (e.g., precancerous lesions). On the other hand, sampling errors due to preselection, and the often low number of cells actually measured, may preclude the possibility of exact cell cycle analysis. This is, in fact, an important additional option of flow cytometry resulting from the high resolution of DNA histograms, which is explained by the large number of cells that can be measured in a short period. Sampling errors in flow cytometry may result from the preparation of single cell suspensions which in certain tumor entities may suppress a varying amount of particularly fragile cells or nuclei. The prognostic significance of DNA ploidy, stem line heterogeneity and S-phase fraction is clearly described in quite a number of tumor entities. Independent of its prognostic value, the cytometric identification of stem lines might be particularly useful in the follow-up of tumor patients, where it may indicate the effectivity of systemic therapy. The development of therapeutic concepts is aptly supported by flow cytometric cell cycle analysis which helps to assess the in vitro effect of combined cytostatics on the proliferative process. Moreover, multiparameter analysis of biopsy samples may provide greater accuracy in characterising individual tumor stem lines and may furthermore help to develop improved protocols for the therapy of solid tumors.

Cytophotometry↗
PubMed1991

Cyto-histological correlates in a colposcopic clinic: a 1-year prospective study.

As part of the Quality Assurance Program, all surgical pathology reports of cervical colposcopic biopsies, cone biopsies, and hysterectomy specimens of 772 consecutive patients were correlated with cytology results for a period of 1 yr. The abnormality in cytology or histology ranged from HPV effect to invasive carcinoma. Cytohistological correlation within one grade of severity was obtained in 662 (86%) cases. On formal review of the remaining 110 (14%) cases, sampling error occurred in 75 cytology smears and in 21 colposcopic biopsies. Screening and interpretation error occurred in 10 smears and four biopsies. In this study the sensitivity of cervical cytology in detecting epithelial abnormalities was 90%, with a positive predictive value of 99.7%. The false-negative rate of cytology was 11% and the false-positive rate 0.26%. The majority (90%) of false negatives were due to sampling error; the rest were due to laboratory error. The sensitivity of colposcopic biopsy was 97% with a positive predictive value of 99.4%. The false-negative rate of biopsy was 2.7% and the false-positive rate 0.5%. Endocervical cells were seen in 48% (370) of smears and absent in 52% (402). However, in both instances the detection rate of squamous abnormality was 90%. Also 43% (33) of smears that showed endocervical cells failed to contain the abnormal cells. Endocervical curettage or cone biopsy in 16 of these 33 cases clearly showed a small CIN-III lesion high in the endocervical canal. We believe that the value of endocervical cells as an indicator of adequacy is questionable.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Interpretation of excessive serum concentrations of digoxin in children.

Between January 1981 and April 1984, excessive serum concentrations of digoxin (5 ng/ml or higher) were recorded in 47 children, aged 2 days to 16 years. In 10 patients, the high concentrations were measured 9.25 to 48 hours after death and were significantly higher than antemortem levels in all cases (8.3 +/- 2.4 (+/- standard deviation) postmortem vs 3.3 +/- 1.5 antemortem, less than 0.0001). In 15 patients (40.5% of the living patients) serum concentrations of 5 ng/ml or higher reflected sampling errors; drug levels were monitored too closely to the administration of a dose. None of these children had toxic manifestations of digoxin. In 10 patients, the excessive concentrations were associated with renal failure and a prolonged elimination half-life (T1/2) of digoxin; in 3 of these patients, there were signs of digoxin toxicity. Six cases were caused by digoxin overdose (accidental ingestions, pharmacy error and a suicide attempt). In 6 additional cases, the existence of an endogenous digoxin-like substance (EDLS) was shown to contribute to the excessive levels of the drug. One case could be attributed to digoxin-amiodarone interaction. In 10 of 37 living patients, digoxin toxicity was diagnosed. After excluding the 15 sampling errors and 6 cases with EDLS, this represents 63% of the cases. There was a good correlation between digoxin elimination T1/2 and serum creatine concentrations (r = 0.71, p less than 0.01). The above observations suggest that excessive serum concentrations of digoxin may not necessarily reflect potentially toxic levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗