Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Sampling Errors”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1991

A morphometrical comparison of right and left whole human vastus lateralis muscle: how to reduce sampling errors in biopsy techniques.

In studies of the effects of different training programmes, one muscle--most commonly the vastus lateralis--is used for the experiment while the contralateral muscle serves as a control, at the same time as muscle biopsies are taken from both sides. In order to increase the reliability of such studies, the sources and the magnitude of the sampling errors in the biopsy techniques need to be assessed in detail. In this study, cross-sections of whole right and left vastus lateralis muscle from six young sedentary right-handed men were prepared, and the total number and size of fibres and the proportion of the different fibre types were calculated. A significant difference (P less than 0.05-P less than 0.001) between the right and the left muscle was found for at least one of the three variables in each of the six men, but there was no systematic difference and, therefore, no significant right-left difference for the whole group. The maximum difference between the right and the left side for the mean fibre size was 25% and for the fibre type proportion 5%; these differences are much smaller than the known variation within individual muscles. In conclusion, any study involving biopsies from both the right and the left vastus lateralis may use either muscle for the experiment while the contralateral muscle serves as a control without leading to systematic sampling error, whereas the errors involved in taking small samples from each muscle are much more important to control and to reduce.

Adult↗
PubMed1986

Sampling error in diagnosing hyperparathyroid changes in bone in small needle biopsies.

Sampling error in diagnosing the effects of hyperparathyroidism on bone was studied retrospectively by subdividing large-core bone biopsy samples and evaluating them histologically. We used intratrabecular osteoclastic tunneling resorption as the diagnostic feature of secondary hyperparathyroidism in 10 hemodialysis patients. All biopsies were taken with a large-core bone biopsy instrument, resulting in a mean biopsy width of 5 mm. The processed tissue slides were divided into halves (mean width 2.5 mm) and subsequently into thirds (mean width 1.6 mm), mimicking smaller bone biopsy instruments such as the Jamshidi needle. In 30% of the cases the diagnosis of secondary hyperparathyroidism would have been missed if taken by a Jamshidi-type needle, and 60% if taken by a needle with a core diameter of 1.6 mm. Our findings emphasize the necessity of utilizing large-core bone biopsies in diagnosing certain metabolic bone diseases.

Biopsy, Needle↗
PubMed1989

Evaluation of postmortem endomyocardial biopsy specimens from 38 patients with lymphocytic myocarditis: implications for role of sampling error.

Among 38 hearts from autopsies in which lymphocytic myocarditis contributed to death, 10 endomyocardial specimens from the apical septal aspect of each ventricle (760 specimens) and 6 slices of ventricular myocardium (228 slices) were evaluated for myocarditis by the Dallas criteria. For each case, the number of positive biopsy samples correlated well with the mean lymphocyte counts in biopsy tissues (P less than 0.0001) and the mean number of inflammatory foci per square centimeter in myocardial slices (P less than 0.001). Right ventricular biopsy specimens, however, were positive in only 63% of the 38 cases and 17% of the 380 specimens. Similarly, left ventricular biopsy tissues were positive in only 55% of the cases and 20% of the specimens. Sampling error was somewhat more prevalent among the 11 cases with isolated myocarditis than in the 27 with myocarditis and other illnesses. Even when 10 biopsy specimens per ventricle were evaluated, the frequency of false-negative results was 45% for the left and 37% for the right ventricle. Although myocarditis was noted in 68% of the 38 septal slices, it involved the subendocardium of the right ventricle (from which biopsy specimens are usually obtained) in only 24%. Because of the mild and focal nature of the inflammatory infiltrates and involvement of regions inaccessible to the bioptome, sampling error contributes appreciably to false-negative results in endomyocardial biopsy tissue from patients with myocarditis. Thus, when myocarditis is evaluated by biopsy alone, only positive findings are considered diagnostic.

Adolescent↗
PubMed2000

Reliability of DNA cytometric S-phase analysis in surgical biopsies: assessment of systematic and sampling errors and comparison between results obtained by image and flow cytometry.

Three major parameters in DNA histograms that contribute to the reliability of S-phase analysis were evaluated. These parameters are (1) the extent of background in relation to the amount of S-phase cells (and the validity of its subtraction), (2) the size of the "free" S-phase range (S(free)), and (3) the sampling error of cell counting. Tests in histograms obtained from surgical biopsies by flow cytometry (FCM) showed that the background subtraction is reliable if the found S-phase fraction is higher than the fraction of background events in the histogram range of the cell population. The size of S(free) was determined in computer-generated test histograms as a function of variables such as the coefficient of variation (CV) and the DNA index (DI). To calculate the sampling error of cell counting above background and in S(free), a model was developed that was validated by experimental data. This error can serve as an indicator of the uncertainty in S-phase analysis. The poor correlation found between %S values measured by image cytometry (ICM) and FCM in surgical biopsies was assigned to high uncertainty by low cell numbers in ICM histograms. A method is proposed to estimate quantitatively the reliability of S-phase analysis that can facilitate the interpretation of results.

Biopsy↗
PubMedDate not supplied

Potential sampling error in fine needle aspiration biopsy of dedifferentiated chondrosarcoma: a report of 4 cases.

BACKGROUND: Dedifferentiated chondrosarcoma is a rare, poorly understood and often fatal sarcoma that usually manifests as a high grade, non-cartilage-producing sarcoma juxtaposed against a low grade chondrosarcoma. A correct diagnosis requires recognition of both components. In the absence of complete resection, rendering a specific diagnosis on small biopsy specimens, such as fine needle aspiration biopsy (FNAB), may be extraordinarily difficult. CASES: We retrospectively reviewed 4 cytology samples (3 primary, 1 metastatic) from 3 patients with dedifferentiated chondrosarcoma, initially analyzed by FNAB, emphasizing the potential for sampling error. Two women, aged 78 and 57 years, both of whom had prior histories of carcinoma, presented with lesions involving the right and left femur, respectively. One 27-year-old man with multiple osteochondromatosis developed a dedifferentiated chondrosarcoma of the left pelvis. Two primary cytologic specimens consisted of moderately cellular smears containing a spindled to polygonal, nonspecific, pleomorphic sarcoma unaccompanied by definite matrix material; 1 of these had a concomitant core needle biopsy (CNB), also demonstrating pleomorphic sarcoma. The third primary cytologic specimen revealed low grade chondrosarcoma, but a concomitant CNB showed only a high grade, non-matrix-producing sarcoma. The last patient developed a metastasis to the opposite femur; FNAB revealed a high grade spindle cell sarcoma. In none of the FNAB or CNB specimens were both low and high grade components of dedifferentiated chondrosarcoma recognized. However, the diagnosis was strongly suspected based on the clinical and radiographic findings. CONCLUSION: Due to sampling error, the diagnosis of dedifferentiated chondrosarcoma may be difficult to establish by cytologic examination alone. Clinical and radiographic correlation is essential for an accurate diagnosis.

Adult↗
PubMed2004

Army ants algorithm for rare event sampling of delocalized nonadiabatic transitions by trajectory surface hopping and the estimation of sampling errors by the bootstrap method.

The most widely used algorithm for Monte Carlo sampling of electronic transitions in trajectory surface hopping (TSH) calculations is the so-called anteater algorithm, which is inefficient for sampling low-probability nonadiabatic events. We present a new sampling scheme (called the army ants algorithm) for carrying out TSH calculations that is applicable to systems with any strength of coupling. The army ants algorithm is a form of rare event sampling whose efficiency is controlled by an input parameter. By choosing a suitable value of the input parameter the army ants algorithm can be reduced to the anteater algorithm (which is efficient for strongly coupled cases), and by optimizing the parameter the army ants algorithm may be efficiently applied to systems with low-probability events. To demonstrate the efficiency of the army ants algorithm, we performed atom-diatom scattering calculations on a model system involving weakly coupled electronic states. Fully converged quantum mechanical calculations were performed, and the probabilities for nonadiabatic reaction and nonreactive deexcitation (quenching) were found to be on the order of 10(-8). For such low-probability events the anteater sampling scheme requires a large number of trajectories ( approximately 10(10)) to obtain good statistics and converged semiclassical results. In contrast by using the new army ants algorithm converged results were obtained by running 10(5) trajectories. Furthermore, the results were found to be in excellent agreement with the quantum mechanical results. Sampling errors were estimated using the bootstrap method, which is validated for use with the army ants algorithm.

Journal Article↗
PubMed2000

Bias and Sampling Error of the Estimated Proportion of Genotypic Variance Explained by Quantitative Trait Loci Determined From Experimental Data in Maize Using Cross Validation and Validation With Independent Samples.

Cross validation (CV) was used to analyze the effects of different environments and different genotypic samples on estimates of the proportion of genotypic variance explained by QTL (p). Testcrosses of 344 F(3) maize lines grown in four environments were evaluated for a number of agronomic traits. In each of 200 replicated CV runs, this data set was subdivided into an estimation set (ES) and various test sets (TS). ES were used to map QTL and estimate p for each run (p(ES)) and its median (p(ES)) across all runs. The bias of these estimates was assessed by comparison with the median (p(TS.ES)) obtained from TS. We also used two independent validation samples derived from the same cross for further comparison. The median p(ES) showed a large upward bias compared to p(TS.ES). Environmental sampling generally had a smaller effect on the bias of p(ES) than genotypic sampling or both factors simultaneously. In independent validation, p(TS.ES) was on average only 50% of p(ES). A wide range among p(ES) reflected a large sampling error of these estimates. QTL frequency distributions and comparison of estimated QTL effects indicated a low precision of QTL localization and an upward bias in the absolute values of estimated QTL effects from ES. CV with data from three QTL studies reported in the literature yielded similar results as those obtained with maize testcrosses. We therefore recommend CV for obtaining asymptotically unbiased estimates of p and consequently a realistic assessment of the prospects of MAS.

Journal Article↗
PubMed2000

Cytologic features of proliferative breast disease: a study designed to minimize sampling error.

BACKGROUND: Assessment of cytologic features that allow accurate classification of proliferative breast disease has been hampered by sampling errors when fine-needle aspirations have been compared with their corresponding histologic sections. METHODS: To allow for optimal cytohistologic correlation, 2 smears (1 hematoxylin and eosin-stained and 1 Diff-Quik-stained) were prepared from each of 98 breast biopsies without mass lesions and compared with the corresponding histologic sections of the scraped area. Each smear was reviewed in a blinded fashion and assessed for cellularity, background elements, cytoarchitectural features of cell groups, and nuclear features by 2 reviewers. Smears were then classified as nonproliferative breast disease (NPBD), proliferative breast disease without atypia (PBD) or with atypia (PBDA), or DCIS, based on review of the corresponding histologic sections. RESULTS: When comparing NPBD/PBD (n = 86) with PBDA/DCIS (n = 12), smears from PBDA/DCIS were significantly (by the Fisher exact test or Wilcoxon rank sum P values with adjustment for multiple comparisons) more likely to be cellular; contain single cells and necrosis; exhibit nuclear overlap and cytoplasmic vacuoles; have large nuclei, macronucleoli, pleomorphism, clumped chromatin, and hyperchromasia; and were less likely to have complex cell groups, monolayers, swirling, cohesion, and myoepithelial cells in epithelial sheets and the smear background. When NPBD (n = 53) and PBD (n = 33) were similarly compared, smears from PBD were more likely to exhibit larger and more complex cell groups, but they were otherwise similar to smears from NPBD. CONCLUSIONS: There are many cytologic features that will allow a distinction of NPBD/PBD from PBDA/DCIS, but relatively few that can aid in separating NPBD from PBD.

Biopsy↗
PubMedDate not supplied

Moisture nonuniformity and sampling errors in large cheddar cheese blocks.

A study was made of the impact of nonuniform moisture distribution in 290 kg blocks of cheese on the accuracy of sampling the cheese for moisture content. The range of moisture from center to outside surfaces of the blocks was about 5%. The temperature gradient, developed in the first 24-48 h after cheese making, drove the moisture migration from warm to cold areas in the cheese blocks during initial cooling. The moisture gradient from center to outside of each block, the non-symmetrical nature of the gradient, and the actual length of the core sample all contributed to random and systemic error in sampling within a single cheese plant. It was concluded that average moisture differences from vat to vat in a factory were small, and large variations in moisture tests were due to sampling errors.

Cheese↗
PubMed1979

Sampling error and observer variation in the interpretation of esophageal biopsies.

Esophageal autopsy specimens from 11 subjects were used to determine observer variation and sampling error in assessing alterations attributed to gastroesophageal reflux. Inter- and intraobserver variation exceeded 20% even when the diagnosis was limited to a normal and abnormal reading. Marked differences in basal cell thickness but not in papillary height occurred when specimens were obtained from different levels of the lower esophagus. The differences were less marked in specimens obtained from the same level. Based on these data the reliability of basal cell thickness and papillary height as an index of gastroesophageal reflux appears limited.

Autopsy↗
PubMed2001

Piffalls in diagnostic molecular pathology--significance of sampling error.

Today, molecular diagnostic tests are widely used in clinical medicine with polymerase chain reaction (PCR)-based techniques being of particular interest. In tissue specimens, however, false-positive and false-negative results can be obtained if pathomorphological and processing aspects are not considered. We therefore studied the impact of tissue sampling in three widely used diagnostic tests: (1) assessment of clonality in B-cell non-Hodgkin's lymphoma, (2) analysis of microsatellite instability (MSI) in colorectal neoplasia, and (3) demonstration of mycobacterium tuberculosis. Tissue sections of routinely formalin-fixed and paraffin-embedded diagnostic specimens were taken, and the significance of sampling was systematically investigated using laser microdissection or processing of the entire section. PCR analyses were done according to standard protocols. False-positive pseudo-monoclonality was obtained in small gastrointestinal biopsies and in laser microdissected lymph follicles of non-neoplastic tonsils. False negativity (pseudo-stability) could be demonstrated in a case with hereditary rectal adenoma if whole tissue sections were taken without microdissection of the most dysplastic subareas. Demonstration of mycobacteria failed in tissue sections of a formalin-fixed lymph node that was positive after complete digestion or in fresh frozen material of the same patient. In diagnostic molecular pathology, sampling error is an important source of false-positive and false-negative results, particularly if disease- and tissue-specific morphological features, such as sample size, type of fixation, and intralesional heterogeneity, are ignored.

Clone Cells↗
PubMed1981

Minimizing sample error in transmission electron microscopy.

The last few years have seen an increase in the use of electron microscopy, both for research and as a diagnostic tool in pathology. With the increase in the number of specimens being used for diagnostic purposes, limitations due to sampling error have become apparent. The method described is designed to help overcome this problem.

Microscopy, Electron↗
PubMed1991

Sampling errors and the precision associated with counting very low numbers of white cells in blood components.

Attention to the accurate and precise measurement of the white cell (WBC) content of transfused products has risen in response to awareness of the potential benefits of WBC-depleted components and the development of technical capabilities to produce these components. The techniques thus far reported have focused on the reliability of detecting a WBC, provided it is present in the test system. The likelihood of selecting a WBC from the product of interest for counting in the analytical system--that is, the sampling error--must also be considered. The occurrence of a WBC in a WBC-depleted component is a rare event and may be modeled with the binomial or the Poisson distribution. Several assay techniques were analyzed by using these distribution models to determine the confidence intervals of the WBC content. The 95-percent confidence intervals spanned more than 2 logs10 for some methods at 3 x 10(5) WBCs per product. It is concluded that the reporting of WBC content for research provides not only the estimate of the mean but also a confidence interval for this estimate. Quality control procedures should be designed to verify that the WBC content is less than the targeted amount and should provide an associated statement of confidence.

Blood Platelets↗
PubMed2002

Sampling error can significantly affect measured hospital financial performance of surgeons and resulting operating room time allocations.

UNLABELLED: Hospitals with limited operating room (OR) hours, those with intensive care unit or ward beds that are always full, or those that have no incremental revenue for many patients need to choose which surgeons get the resources. Although such decisions are based on internal financial reports, whether the reports are statistically valid is not known. Random error may affect surgeons' measured financial performance and, thus, what cases the anesthesiologists get to do and which patients get to receive care. We tested whether one fiscal year of surgeon-specific financial data is sufficient for accurate financial accounting. We obtained accounting data for all outpatient or same-day-admit surgery cases during one fiscal year at an academic medical center. Linear programming was used to find the mix of surgeons' OR time allocations that would maximize the contribution margin or minimize variable costs. Confidence intervals were calculated on these end points by using Fieller's theorem and Monte-Carlo simulation. The 95% confidence intervals for increases in contribution margins or reductions in variable costs were 4.3% to 10.8% and 6.0% to 8.9%, respectively. As many as 22% of surgeons would have had OR time reduced because of sampling error. We recommend that physicians ask for and OR managers get confidence intervals of end points of financial analyses when making decisions based on them. IMPLICATIONS: The common approach of using one fiscal year of perioperative accounting data can be insufficient to prevent random error from influencing important management decisions. When accounting data are used for hospital and operating room management decision making, confidence intervals should be calculated for the key financial variables (e.g., variable cost per hour of operating room time).

Costs and Cost Analysis↗
PubMed1975

Variations in the apparent nutrient content of foods: a study of sampling error.

1. Successive portions of boiled and mashed potatoes, roast pork, cooked, freeze-dried peas and ice-cream were taken in order to determine the total (sampling and experimental) error involved in the 'duplicate analysis' method of dietary survey. 2. These samples were analysed for water, nitrogen, fat, iron and energy. 3. The experimental error of the methods was also studied separately. 4. The sampling and experimental errors ranged from 0-3% for water in potatoes, to 23% for Fe in ice-cream. Sampling error was significantly greater than experimental error for all nutrients studied. 5. It is concluded that in reporting the results from dietary surveys, it is necessary to take account of the erros inherent even in the most precise methods.

Analysis of Variance↗