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At least 73 records · Page 4Linked to original sources
PubMed1991

Cytology of treated and minimal Pneumocystis carinii pneumonia and a pitfall of the Grocott methenamine silver stain.

To clarify the role of foamy alveolar casts (FACs) in the diagnosis of Pneumocystis carinii pneumonia (PCP), we retrospectively reviewed Papanicolaou (Pap)- and Grocott methenamine silver (GMS)-stained slides from 205 bronchial specimens submitted for suspected opportunistic lung infection. FACs containing sporozoites were seen in 86 cases, all with positive GMS. FACs were absent in 119 cases with negative GMS. In patients previously treated for PCP, Pap showed FAC-like material which lacked sporozoites. GMS demonstrated clumped degenerated Pneumocystis carinii (PC) cysts. In 17 GMS-positive cases there were no FACs on Pap due to sampling error and low burden of organisms. Morphologic features of macrophages in these cases can suggest the presence of PC. When FACs are lacking, a special stain is required. When GMS is used, the control must contain PC to avoid a false negative GMS. The inconsistent uptake of GMS by PC is a pitfall which is distinct from sampling error and which to our knowledge has not been previously reported.

Bronchi↗
PubMed1990

Fine needle aspiration diagnosis of intraabdominal and retroperitoneal lymphomas by a morphologic and immunocytochemical approach.

We reviewed 238 fine needle aspiration biopsies (FNA) of intraabdominal or retroperitoneal (IA/RP) masses in 192 patients with known or suspected lymphoma. A limited battery of immunocytochemical stains, including kappa (k) and lambda (l) light chains and Leu-4, was performed in 104 aspirates. On hundred twenty-eight of the FNA were diagnostic of or consistent with lymphoma, and three were diagnostic of carcinoma. Twenty-eight were considered negative for malignancy and 79 were suspicious for lymphoma or were nondiagnostic. For 135 of the FNA, a histologic biopsy specimen was available for comparison purposes. Overall, only one false-positive result was seen in a specimen lacking immunocytochemical data. The sensitivity of FNA lymphoma diagnosis was 66%. False-negative results due to sampling error were not uncommon, giving a predictive value of a negative result as 42%. The classification of the lymphomas by FNA was identical to that of the surgical biopsy in 86% of specimens and concurrently discrepant in 6%. We conclude that the routine performance of immunocytochemical studies on FNA of IA/RP masses is a feasible and valuable technique. Whereas suboptimal sensitivity and sampling error may make a negative diagnosis unreliable, lymphoma marker studies (combined with morphology) allow for an accurate and confident diagnosis and subclassification of lymphoma in the majority of cases.

Abdominal Neoplasms↗
PubMed1991

National Survey of Family Growth: design, estimation, and inference.

The purpose of this report is to document the procedures used in the 1988 National Survey of Family Growth (NSFG) to select the sample, weight the data to produce national estimates, impute missing data, and estimate sampling errors. Therefore, this report necessarily contains a great deal of technical detail. For readers who do not need this level of detail, this summary briefly describes the procedures used. The National Survey of Family Growth is conducted every few years by the National Center for Health Statistics (NCHS), a part of the U.S. Department of Health and Human Services. The purpose of the survey is to collect and publish data from a national sample of women on childbearing, factors affecting childbearing (such as contraception, sterilization, and infertility), and related aspects of maternal and infant health. Interviewing for Cycle IV of the survey was done in 1988 by Westat, Inc., under a contract with NCHS. Personal interviews were conducted between January and August of 1988 with a national sample of 8,450 women in the civilian noninstitutionalized population of the United States. Interviews were conducted in person by trained female interviewers and lasted an average of 70 minutes. The interview focused on the woman's pregnancies, if any; her use of contraception; her ability to bear children (fecundity and infertility); her use of medical services for family planning, infertility, and prenatal care; her marriage and cohabitation history, if any; and a wide range of demographic and economic characteristics. This report describes some of the main methodological aspects of the survey, including the sample design, weighting, sampling errors, and imputation of missing data. These topics will be described briefly and less technically in this summary. Each topic is discussed in more detail in the rest of the report.

Adolescent↗
PubMed1989

An explanation for the problem of false-negative cervical smears.

False-negative cervical cytology due to sampling error is a well-recognized problem. Forty-seven women with histologically proven cervical intraepithelial neoplasia (CIN) were studied. All had two cervical smears performed at a mean interval of 3 months. At the time of the second smear, cervicography, colposcopy and biopsy were performed. The area of acetowhite cervical lesions and of the total visible atypical transformation zone (ATZ) were measured from the cervical photographs. The 17 women in whom one or both smears showed no dyskaryosis were found to have a significantly smaller proportion of their ATZ affected by CIN. It is suggested that this finding can account for the sampling error which causes false-negative cervical cytology. New screening techniques, such as cervicography, may offer a method of detecting and assessing these relatively smaller cervical lesions.

Biopsy↗
PubMed1983

Classical statistical considerations in medical decision models.

The influence of sampling error on decision-analytic models was investigated to determine how these errors affect model reliability. Formulas were developed to relate statistical error in the probability decision threshold and gain in expected utility to the error in the data samples upon which such models are based. The formulas were validated in a simulation experiment and then applied to a hypothetical decision model and to the clinical problem of immediate surgery versus continued observation in suspected acute appendicitis. The results of this analysis show that modest statistical error affecting any variable in a decision model may be amplified into a substantially larger error in both the probability decision threshold and the gain in utility predicted by the model. In addition, when errors are present simultaneously in several variables, they may compound to unexpectedly large magnitudes, rendering the model unreliable over a wide range of disease probability. The interpretation of the results of a decision analysis should be viewed along a continuum that takes into account both the magnitude of the gain or loss in expected utility predicted by the model and a quantitative measure of the reliability of this prediction. Whenever possible, a determination of statistical error should be an integral part of any formal decision analysis.

Acute Disease↗
PubMed1978

The importance of beta, the type II error and sample size in the design and interpretation of the randomized control trial. Survey of 71 "negative" trials.

Seventy-one "negative" randomized control trials were re-examined to determine if the investigators had studied large enough samples to give a high probability (greater than 0.90) of detecting a 25 per cent and 50 per cent therapeutic improvement in the response. Sixty-seven of the trials had a greater than 10 per cent risk of missing a true 25 per cent therapeutic improvement, and with the same risk, 50 of the trials could have missed a 50 per cent improvement. Estimates of 90 per cent confidence intervals for the true improvement in each trial showed that in 57 of these "negative" trials, a potential 25 per cent improvement was possible, and 34 of the trials showed a potential 50 per cent improvement. Many of the therapies labeled as "no different from control" in trials using inadequate samples have not received a fair test. Concern for the probability of missing an important therapeutic improvement because of small sample sizes deserves more attention in the planning of clinical trials.

Clinical Trials as Topic↗
PubMed1990

Rapid immunotyping of B-cell non-Hodgkin's lymphomas by flow cytometry. A comparison with the standard frozen-section method.

The authors compared immunotyping (IT) results obtained by both standard frozen section (FS) and flow cytometry (FC) methods on 218 biopsies suggestive of lymphoma to learn the advantages of each method. The independent interpretations of the FS and FC IT results were concordant in 93% (202 of 218) of cases. The 16 cases with discordance were reviewed and seven causes for discrepancy found: methodologic problems, focal lymphomatous involvement, more sensitive light chain detection by FC, inadequate sample for FC, interpretation error, sample mislabeling for FC, and unexplained. Eleven of the concordant B-cell non-Hodgkin's lymphomas (NHLs) studied by FC did not have a kappa:lambda ratio of 3 or greater or 0.5 or less and were shown to express light chain restriction by a D-value of 15 or greater with the use of statistical analysis of the kappa and lambda histograms or by multiparameter analysis of large versus small cells. The authors found both methods to be effective for phenotyping lymphomas, however, each has distinct features, making them complementary in their applications.

Antibodies, Monoclonal↗
PubMed1976

A propagation of error analysis of the enzyme activity expression. A model for determining the total system random error of a kinetic enzyme analyzer.

We present a total system error evaluation of random error, based on a propagation of error analysis of the expression for the calculation of enzyme activity. A simple expression is derived that contains terms for photometric error, timing uncertainty, temperature-control error, sample and reagent volume errors, and pathlength error. This error expression was developed in general to provide a simple means of evaluating the magnitude of random error in an analytical system and in particular to provide an error evaluation protocol for the assessment of the error components in a prototype Miniature Centrifugal Analyzer system. Individual system components of error are measured. These measured error components are combined in the error expressiion to predict performance. Enzyme activity measurements are made to correlate with the projected error data. In conclusion, it is demonstrated that this is one method for permitting the clinical chemist and the instrument manufacturer to establish reasonable error limits.

Aspartate Aminotransferases↗
PubMed1986

Parameters that bias the measurement of airborne concentration within a respirator.

This paper describes the theoretical basis upon which a test system has been set up to evaluate the sampling error associated with in-facepiece sampling on half-mask respirators. The in-facepiece sampling technique evaluated in this study is the one currently used in the U.S. to conduct quantitative facepiece fit testing. An experimental design was developed to study the sampling bias associated with in-facepiece sampling when selected parameters of the man/respirator system were varied. The results indicated that significant errors can be made in estimating concentration within a respirator when the current in-facepiece sampling technique is employed. Sampling bias was determined when in-facepiece samples were collected only during the inhalation phase of the respiratory cycles. They were found to range from greater than -99% to greater than +98%. The mean sampling bias was -17 +/- 38%. When measured in-facepiece concentrations were used to calculate a fit factor the resulting range was 44 to 4728 even though the actual fit factor was only 87. Based upon the data presented, it was hypothesized that faceseal leakage was streamlining within the respirator cavity. As a result, quantitative facepiece fit data on half-mask respirators may be biased by the large measurement error.

Acetone↗
PubMed1991

Protonation of interacting residues in a protein by a Monte Carlo method: application to lysozyme and the photosynthetic reaction center of Rhodobacter sphaeroides.

We used Monte Carlo methods to treat statistical problem of electrostatic interactions among many titrating amino acids and applied these methods to lysozyme and the photosynthetic reaction center of Rhodobacter sphaeroides, including all titrating sites. We computed the average protonation of residues as a function of pH from an equilibrium distribution of states generated by random sampling. Electrostatic energies were calculated from a finite difference solution to the linearized Poisson-Boltzmann equation using the coordinates from solved protein structures. For most calculations we used the Metropolis algorithm to sample protonation states; for strongly coupled sites, we substantially reduced sampling errors by using a modified algorithm that allows multiple site transitions. The Monte Carlo method agreed with calculations for a small test system, lysozyme, for which the complete partition function was calculated. We also calculated the pH dependence of the free energy change associated with electron transfer from the primary to the secondary quinone in the photosynthetic reaction center. The shape of the resulting curve agreed fairly well with experiment, but the proton uptake from which the free energy was calculated agreed only to within a factor of two with the observed values. We believe that this discrepancy resulted from errors in the individual electrostatic energy calculations rather than from errors in the Monte Carlo sampling.

Electron Transport↗
PubMed1985

Time sampling and measurement error: the effect of interval length and sampling pattern.

The accuracy of momentary time-sampling was evaluated for behaviors occurring for different proportions of time, for different momentary time-samples and for sessions of different lengths. For 1-hr sessions, momentary time-samples of 10, 20 or 30 see intervals between observations yielded 90% of estimates within 10% of the comparison standard, for behaviours of 25%, 50% and 70%. Behaviours occurring for 2% of the session were not accurately recorded even at 10-sec momentary time-samples. For a 5-min momentary time-sample, this criterion was only approached when 8 hr data was averaged to give a single score for each individual, for behaviours of 25% or more. The 5-min momentary time-sample was also compared with a 1 in 5-min cluster sample; although less accurate, cluster-sampling might be a useful strategy in some settings.

Behavior↗
PubMed1983

Adaptive control of theophylline therapy: importance of blood sampling times.

A two-observation protocol for estimating theophylline clearance during a constant-rate intravenous infusion is used to examine the importance of blood sampling schedules with regard to the information content of resulting concentration data. Guided by a theory for calculating maximally informative sample times, population simulations are used to assess the effect of specific sampling times on the precision of resulting clearance estimates and subsequent predictions of theophylline plasma concentrations. The simulations incorporated noise terms for intersubject variability, dosing errors, sample collection errors, and assay error. Clearance was estimated using Chiou's method, least squares, and a Bayesian estimation procedure. The results of these simulations suggest that clinically significant estimation and prediction errors may result when using the above two-point protocol for estimating theophylline clearance if the time separating the two blood samples is less than one population mean elimination half-life.

Blood Specimen Collection↗
PubMed1988

Comparison of two techniques for obtaining samples for coagulation studies: venipuncture and intraarterial line.

The purpose of this study was to compare blood coagulation values drawn by venipuncture and from an intraarterial catheter. A 10 ml discard was obtained from 50 consecutive patients before obtaining the coagulation sample from the intraarterial catheter, and a 0.5 ml discard was obtained from the venipuncture specimen. A two-tailed t test for related samples was performed. The results revealed no significant difference between the two methods (p less than 0.05). The small differences seen were attributed to sampling error. These results suggest that blood samples obtained from heparinized intraarterial catheters after a 10 ml discard provide an accurate assessment of patients' mean clotting time.

Adult↗
PubMed1988

Stability of arterial concentrations during continuous inhalation of C15O2 and 15O2 and the effects on computed values of CBF and CMRO2.

Stability of arterial whole blood and plasma concentrations is a basic requirement in the application of the oxygen-15 (15O2) steady-state inhalation technique for measuring regional cerebral blood flow and oxygen use. The level of stability obtainable in practice is reported in the form of retrospectively analysed blood data from 626 consecutive studies in patients with a range of clinical conditions. Serial arterial whole blood and plasma concentrations were measured during both C15O2 and 15O2 inhalations, and coefficients of variation were calculated. In addition, these concentrations were compared with the corresponding values recorded at the start of each study and maximum variations were calculated. For all four concentrations, mean and median coefficients of variation were around 5 and 4%, respectively. Mean and median maximum variations were around 9 and 7%, respectively. The effects of these variations on the calculations of regional cerebral blood flow, oxygen extraction, and oxygen use were estimated. Mean expected errors were found to be between 4 and 9%, and median expected errors between 3 and 6%. Inherent blood sampling errors were assessed from blood volume studies using 11CO-labeled red cells. These errors were found to be less than 3%.

Arteries↗