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PubMed1976

Apparent anomalies in nuclear feulgen-DNA contents. Role of systematic microdensitometric errors.

The Feulgen-DNA contents of human leukocytes, sperm, and oral squames were investigated by scanning and integrating microdensitometry, both with and without correction for residual distribution error and glare. Maximally stained sperm had absorbances which at lambdamax exceeded the measuring range of the Vickers M86 microdensitometer; this potential source of error could be avoided either by using shorter hydrolysis times or by measuring at an off-peak wavelength. Small but statistically significant apparent differences between leukocyte types were found in uncorrected but not fully corrected measurements, and some apparent differences disappeared when only one of the residual instrumental errors was eliminated. In uncorrected measurements, the apparent Feulgen-DNA content of maximally stained polymorphs measured at lambdamax was significantly lower than that of squames, while in all experimental series uncorrected measurements showed apparent diploid:haploid ratios significantly greater than two. In fully corrected measurements no significant differences were found between leukocytes and squames, and in four independent estimations the lowest diploid:haploid ratio found was 1.99 +/- 0.05, and the highest 2.03 +/- 0.05. Discrepancies found in uncorrected measurements could be correlated with morphology of the nuclei concerned. Glare particularly affected measurements of relatively compact nuclei such as those of sperm, polymorphs and lymphocytes, while residual distribution error was especially marked with nuclei having a high perimeter:area ratio (e.g. sperm and polymorphs). Uncorrected instrumental errors, especially residual distribution error and glare, probably account for at least some of the previously reported apparent differences between the Feulgen-DNA contents of different cell types. On the basis of our experimental evidence, and a consideration of the published work of others, it appears that within the rather narrow limits of random experimental error there seems little or no reason to postulate either genuine differences in the amounts of DNA present in the cells studied, or nonstoichiometry of a correctly performed Feulgen reaction.

Cell Nucleus↗
PubMed1992

Reliability of body-fat estimations from a four-compartment model by using density, body water, and bone mineral measurements.

Reliability of body-fat estimation by a four-compartment model was tested in 10 subjects. Body densities were measured by underwater weighing (UWW), total body water (TBW) by deuterium dilution, and total body bone mass (TBBM) by dual-energy x-ray absorptiometry in three sessions in 1 wk. Percent body fat was determined by [2.559/density -0.734 (TBW/weight) +0.983 (TBBM/weight) -1.841] x 100. Reliability coefficients were 0.991 and 0.994, and within-subjects standard deviations were +/- 1.0 and +/- 1.1 for percent body-fat estimations from Siri's two-compartment and the four-compartment models, respectively; fat mass was +/- 0.8 kg with both models. These data suggest that additive errors in the multicompartment model do not offset the improved accuracy of fat estimations over those obtained from UWW alone. The greatest source of error came from UWW procedure itself (+/- 0.002 g/cm3, or approximately 1.0% of body weight), followed by error in TBW (+/- 0.5 L). More reproducible passive methods that are not dependent on hydration or TBBM may be especially useful after validation against the four-compartment model.

Absorptiometry, Photon↗
PubMed2006

Food composition database development for between country comparisons.

Nutritional assessment by diet analysis is a two-stepped process consisting of evaluation of food consumption, and conversion of food into nutrient intake by using a food composition database, which lists the mean nutritional values for a given food portion. Most reports in the literature focus on minimizing errors in estimation of food consumption but the selection of a specific food composition table used in nutrient estimation is also a source of errors. We are conducting a large prospective study internationally and need to compare diet, assessed by food frequency questionnaires, in a comparable manner between different countries. We have prepared a multi-country food composition database for nutrient estimation in all the countries participating in our study. The nutrient database is primarily based on the USDA food composition database, modified appropriately with reference to local food composition tables, and supplemented with recipes of locally eaten mixed dishes. By doing so we have ensured that the units of measurement, method of selection of foods for testing, and assays used for nutrient estimation are consistent and as current as possible, and yet have taken into account some local variations. Using this common metric for nutrient assessment will reduce differential errors in nutrient estimation and improve the validity of between-country comparisons.

Agriculture↗
PubMed2001

Measuring and reporting errors in surgical pathology. Lessons from gynecologic cytology.

Substantial improvements in measuring and reporting errors in gynecologic cytology have been made during the last decade. Measuring and reporting errors in surgical pathology recently has gained renewed interest. However, review of current literature demonstrates mistakes in how these data are measured and reported. Error rates have been reported from review of consecutive material, biopsy material, and consultation material and range from 0.25% to 43%. Errors have been divided into anatomic regions and specimen types and separated according to their clinical significance. However, to be comparable, errors must be reported in reference to the incidence of disease and not to overall caseload. Blinding and reviewer error have been addressed only rarely, and the true incidence of errors is almost certainly higher than reported. "Gold standards" are not well defined. In addition, available data strongly suggest that the greatest source of error is with false-negative diagnoses, which are detected only rarely by review of consultation material. Most of these issues have been addressed in the gynecologic cytology literature. Errors in surgical pathology are more common than generally believed, and efforts should be made to define methods that allow appropriate interlaboratory comparisons.

Cytodiagnosis↗
PubMedDate not supplied

The validity of a province-wide student drug use survey: lessons in design.

This study assesses the validity and reliability of a province-wide survey on drug use by high school students in Nova Scotia in 1991. The Nova Scotia instrument was derived from the prototype provided in the Canadian guidelines for self-reported adolescent drug use surveys. To our knowledge, this is the first study on the validity and reliability of the Canadian instrument, as applied in a province, since 1978. Two new methods are proposed as validity and reliability checks: a statistical method to assess possible exaggeration by the group claiming to have used a fictitious drug, and a method to review the entire instrument based on responding error distributions. Overall, this study provides strong evidence of the validity and reliability of the items specifically about drug use. The major source of error uncovered using the responding error distributions, was related to instrument design and occurred in items considered to be explanatory variables for drug use.

Adolescent↗
PubMedDate not supplied

Confidence intervals and sample-size calculations for the sisterhood method of estimating maternal mortality.

The sisterhood method is an indirect method of estimating maternal mortality that has, in comparison with conventional direct methods, the dual advantages of ease of use in the field and smaller sample-size requirements. This report describes how to calculate a standard error to quantify the sampling variability for this method. This standard error can be used to construct confidence intervals and statistical tests and to plan the size of a sample survey that employs the sisterhood method. Statistical assumptions are discussed, particularly in relation to the effective sample size and to effects of extrabinomial variation. In a worked example of data from urban Pakistan, a maternal mortality ratio of 153 (95 percent confidence interval between 96 and 212) deaths per 100,000 live births is estimated.

Age Factors↗
PubMed2000

Mistakes on EUS staging of colorectal carcinoma: error in interpretation or deception from innate pathologic features?

BACKGROUND: Because endoscopic ultrasound (EUS) accuracy for staging gastrointestinal tract tumors is limited by many factors, this study was designed to analyze potential sources of error in the EUS staging of colorectal carcinoma. METHODS: All patients referred for EUS evaluation of colorectal carcinoma were staged prospectively by one ultrasonographer and retrospectively by two others with EUS videotape recordings. Pathologic staging was done independently in a blinded fashion. Deceptive pathologic features were defined for T staging by presence of inflammation extending beyond tumor or microscopic spread without inflammation extending to a level consistent with the next stage, and for N staging by large (> or = 10 mm) benign lymph nodes or small (< 10 mm) malignant lymph nodes. RESULTS: Of 22 patients entered into the study, an inflammatory reaction around microscopic tumor spread thought to actually enhance detection by EUS was present in 57.1% of cases. Nine deceptive pathologic lesions were present in 36.4% (8 of 22) of patients (5 T stage, 4 N stage lesions). Of 40 T and N stage mistakes made by the three physicians, 45% were made in the presence and 55% in the absence of deceptive pathologic lesions. Accuracy increased significantly from the presence to absence of deceptive pathologic lesions, from 53.3% to 83.7% (p = 0.029) for T stage, and 8.3% to 73. 1% for N stage (p = 0.0001). Confidence of T staging correlated significantly with accuracy, increasing from 63.3% when unsure to 88. 2% with staging certainty (p = 0.017), an effect not seen for N staging. CONCLUSIONS: Inflammation and desmoplasia around colorectal carcinoma are often present, but may actually enhance EUS detection of microscopic tumor spread. Deceptive pathologic lesions are present in only one third of patients, but account for almost half (45%) of the errors in T and N staging by EUS. Diagnostic accuracy for EUS was increased with confidence in T stage assessment (but not N stage) and in the absence of deceptive pathologic lesions. Errors in interpretation still accounted for the majority of mistakes (55%) made in EUS staging of colorectal carcinoma.

Adult↗
PubMed2006

Specimen labeling QI project cuts error rate.

Up to 70% of all medical decisions are based on lab results. From the beginning, initiative leaders looked at process, not individuals. By analyzing work flow, a number of potential sources for errors were uncovered.

Boston↗
PubMed2004

Medication error reporting in long term care.

BACKGROUND: Medication errors are common causes of medical error in the long-term care (LTC) setting. Despite their frequency and potential clinical impact, most medication errors in LTC facilities remain unreported. Before better reporting systems can be developed to reduce clinically significant medication errors, it is necessary to understand how current medication error reporting systems function. OBJECTIVE: This study describes the medication use and medication error reporting processes, and characterizes the knowledge, attitudes, and beliefs about medication errors of the nursing staff at a single LTC facility. METHODS: Three methods were used to characterize the medication use and medication error reporting processes and the nursing staff's perceptions about such errors. First, key elements and basic processes were defined through observation and semi-structured interviews. Second, medication error reports were reviewed and summarized over a 21-month period. Third, nursing facility staff were surveyed about their knowledge, attitudes, and beliefs concerning medication errors. RESULTS: The medication use process in the LTC setting is similar to that employed in the acute care setting, consisting of 5 steps: prescribing, documenting, dispensing, administering, and monitoring. In the facility studied, an average of 4.7 medication error reports were submitted per month. Staff felt that half of all medication errors were identified and communicated informally through change-of-shift reports rather than through medication error reports. Most staff (85%) believed that disciplinary action was taken against the person who committed an error. CONCLUSIONS: The medication error policies and processes of the LTC facility studied were associated with a low frequency of formal reporting, a narrow perspective on the sources of error, and concerns about disciplinary action. Research is needed to better identify errors, develop interventions that broaden the monitoring perspective to include all health care professionals, reduce the work of reporting, standardize the information collected, and create an institutional atmosphere of participation rather than punishment.

Data Collection↗
PubMed2001

2-D motion estimation using two parallel receive beams.

We describe a method for estimating 2-D target motion using ultrasound. The method is based on previous ensemble tracking techniques, which required at least four parallel receive beams and 2-D pattern matching. In contrast, the method described requires only two parallel receive beams and 1-D pattern matching. Two 1-D searches are performed, one in each lateral direction. The direction yielding the best match indicates the lateral direction of motion. Interpolation provides sub-pixel magnitude resolution. We compared the two beam method with the four beam method using a translating speckle target at three different parallel beam steering angles and transducer angles of 0, 45, and 90 degrees. The largest differences were found at 90 degrees, where the two beam method was generally more accurate and precise than the four beam method and also less prone to directional errors at small translations. We also examined the performance of both methods in a laminar flow phantom. Results indicated that the two beam method was more accurate in measuring the flow angle when the flow velocity was small. Computer simulations supported the experimental findings. The poorer performance of the four beam method was attributed to differences in correlation among the parallel beams. Specifically, center beams 2 and 3 correlated better with each other than with the outer beams. Because the four beam method used a comparison of a kernel region in beam pair 2-3 with two different beam pairs 1-2 and 3-4, the 2-to-1 and 3-to-4 components of this comparison increased the incidence of directional errors, especially at small translations. The two beam method used a comparison between only two beams and so was not subject to this source of error. Finally, the two beam method did not require amplitude normalization, as was necessary for the four beam method, when the two beams were chosen symmetric to the transmit axis. We conclude that two beam ensemble tracking can accurately estimate motion using only two parallel receive beams.

Biomedical Engineering↗
PubMed1988

The reliability of alcohol abusers' self-reports of drinking and life events that occurred in the distant past.

This study investigated the test-retest reliability of 69 alcohol abusers' current reports about their past (approximately 8 years prior to interview) drinking behavior and life events. Drinking behavior was assessed by the Lifetime Drinking History (LDH) questionnaire and life events were assessed using the Recent Life Changes Questionnaire (RLCQ). Reliability coefficients for LDH variables were generally moderate to high (r = .52 to .81). Using empirical criteria, the diagnostic power of the two LDH interviews to classify correctly subjects as either having had or not having had a drinking problem was quite high. The reliability coefficient for the RLCQ was r = .85 and 91.7% of the identified events were reported in both interviews. Similarly high test-retest reliabilities and individual event agreement rates were obtained for the six homogeneous subscales of the RLCQ. Subjects were also asked why they had given inconsistent answers to life events questions in the two interviews. Inconsistencies often resulted from errors in the temporal placement of events or from misunderstanding items, rather than from failure to recall an event; this suggests that some sources of error in recalling life events can be reduced. It is concluded that alcohol abusers' reports of drinking and life events occurring many years prior to the date of interview are generally reliable. This finding is consistent with previous studies showing high test-retest reliabilities for reports of recent drinking and related events.

Adult↗
PubMed2000

"The scarlet E": the presentation of epilepsy in the English language print media.

OBJECTIVE: To examine the coverage of epilepsy in English language newspapers and magazines to determine how they portray the medical risks associated with epilepsy, whether they report research and treatment advances accurately, whether stigmatizing biases toward persons with epilepsy persist, and to examine the sources of errors in reporting about epilepsy. BACKGROUND: The print media reflect and shape current views about epilepsy and other neurologic conditions. They also have the potential to further misconceptions about neurologic issues and particular brain disorders. Persistent myths about epilepsy, such as the ancient belief that it is a demonic disorder, can result in discrimination, emotional difficulties, and reluctance to seek effective treatment. METHODS: A large commercial database was used to search for stories about epilepsy from approximately 2,000 English language newspapers and popular magazines. Two epileptologists independently classified story themes and main sources, and screened for the presence of gross errors in 210 stories about epilepsy or seizures. The authors analyzed the metaphors and terminology used to describe seizures and epilepsy. RESULTS: The majority of English language print stories about epilepsy were accurate depictions of social and medical issues regarding the disorder, most commonly depictions of persons overcoming epilepsy and announcements of new therapies and reports of scientific advances. Thirty-one percent of the stories, however, contained gross errors, most commonly scientific inaccuracy, exaggerated treatment claims, and overestimates of the risks of dying during a seizure. New drug therapies were often described inaccurately by physicians and pharmaceutical spokespersons as curative and without side effects. Patients and their families frequently overemphasized the risk of dying during a seizure and misstated medical issues. Most celebrities with recurring seizures denied having epilepsy. Seizures were described with demonic imagery in 6% of stories. United States epilepsy associations discourage labeling patients as "epileptics"; however, the term was used in 45% of stories. CONCLUSION: Physicians and reporters should be aware of both professional and popular biases that influence the print media's presentation of the causes and consequences of epilepsy.

Anticonvulsants↗
PubMed2005

Estimation of renal extraction fraction based on postcontrast venous and arterial differential T1 values: an error analysis.

An error analysis for quantifying single kidney extraction fraction (EF) via differential T1 measurements in the renal vein (RV) and renal artery (RA) is presented. Sources of error include blood flow effects, the effect of a short repetition time (TR), and the impact of uncertainties in the T1 estimates on the final EF calculations. Blood flow effects were investigated via simulation. For a range of blood velocities in the renal vein that may be found in kidney disease, incomplete refreshment of blood between readouts results in significant errors in T1 estimation. For a .5-cm slice, 110-ms sampling interval, and T1 of 600 ms, T1 estimation to within 5% of true T1 requires an average through-plane velocity of 6.75 cm/s for parabolic flow, and 3.5 cm/s for plug flow. Improvement can be achieved by accurately estimating the fraction of blood that has not refreshed between readouts (f(old)), while the quality of the T1 estimate varies with the accuracy of f(old) estimation. Shortening of the TR was investigated using phantom and in vivo studies. T1 was estimated to within 3% of the true value on phantoms, and within 5% of the true value for flowing blood for TR = 2T1. The estimated EF is shown to be very sensitive to the difference between T(1RA) and T(1RV). To achieve 10% or 20% uncertainty in the EF estimate, T1 in the renal vein and renal artery must be estimated to within approximately 1% or 2%. Because of limitations on measurement accuracy and precision, this method appears to be impractical at this time.

Blood Flow Velocity↗
PubMed1997

Circular trajectory formation during blind locomotion: a test for path integration and motor memory.

Eight healthy subjects were asked to walk blindfolded along circular paths of different radii after several practice trials with vision. Their task was to stop after completing two full revolutions. They always walked counter-clockwise (CCW) in (a) a control condition (CONTROL), including the instructions mentioned above, (b) with the further instruction to count backwards in twos (MENTAL), (c) with the instruction to count loudly (LOUD). The movement of two markers lying along the head naso-occipital axis was recorded by means of an ELITE system. Total walked distance (DISTANCE), total head turning angle (ANGLE) and average radius (RADIUS) of the trajectories performed were measured. All subjects were able to perform approximately circular trajectories. They consistently overshot the ideal radius independently of the condition and circle size, undershot the total angle and overshot total distance. The LOUD condition induced greater errors in the performance but only on total distance (P<0.05). A strong correlation was found between the errors in radius and total distance but not between distance and total angle. Principal components analysis suggested that radius and distance share a common source of errors while total angle produced independent errors. The results indicate that (a) circular trajectories can be generated starting from spatial and/or motor memory, without the aid of visual information; (b) the task needs some attentional control and does not involve simple automatic processing of afferent information; (c) different sensory information or different processing modes are probably involved in the estimation of the curvature and length of the walked path on the one hand, and of the total rotation angle on the other.

Adult↗
PubMed2005

Using cancer registry data for survival studies: the example of the Ontario Cancer Registry.

BACKGROUND AND OBJECTIVES: The Ontario Cancer Registry (OCR) is a population-based tumor registry created to provide data for epidemiologic research and for cancer surveillance. Recently it has been used for health services research. The objective of this project was to assess the quality of the OCR data that is used in survival analysis. METHODS AND DESIGN: Clinical information for 898 patients with squamous carcinoma of the head and neck including index tumor site, date of diagnosis, vital status, date of death, and cause of death from a prospective database at the Kingston Regional Cancer Center is compared to the same data elements in the OCR for the same patients. RESULTS: There is no statistically significant difference in disease-specific survival between the information from the two databases (log rank P = .89). The OCR captured and correctly assigned index tumor site for 81.4% (detection rate). The site assignment was accurate 90.9% of the time (confirmation rate), there was agreement on vital status (dead vs. alive) for all but one patient, and there was excellent agreement on date of death. However, cause of death (cancer vs. noncancer) based on death certificates had a 31% error rate. CONCLUSION: Researchers can be confident in the survival analysis generated from data in this registry, but need to be aware of potential sources of error.

Carcinoma, Squamous Cell↗
PubMed2002

Improving lesion conductivity estimate by means of EEG source localization sensitivity to model parameter.

EEG-based source localization techniques use scalp-potential data to estimate the location of underlying neural activity. EEG source location reconstruction requires the assumption of a source model and the assumption of a conductive head model. Brain lesions can present conductivity values that are dramatically different from those of surrounding normal tissues and have to be included in head models for accurate neural source reconstruction. It is therefore necessary to analyze subjects' anatomic images (using MRI or computed tomography) to identify lesion type and to assign the appropriate conductivity value. Source localization accuracy may be influenced by uncertainties in tissue conductivity assignment during head model construction. The authors present a sensitivity study quantifying the effect of uncertainty in brain lesion conductivity assignment on EEG dipole source localization. They adopted an eccentric-spheres head model in which an eccentric bubble approximated the effects of actual brain lesions. After simulating EEG signal measurement in 64 different pathologic situations, an inverse dipole fitting procedure was carried out, assuming an incorrect lesion conductivity assignment ranging from a half to twice the real value. Incorrect lesion conductivity assignment led to markedly wrong source reconstruction for highly conductive lesions like liquid-filled ones (localization errors as much as 1.7 cm). Conversely, low sensitivity to uncertainties in conductivity assignment was found for lesions with low conductivity like calcified tumors. The authors propose a method based on residual error analysis to improve the lesion conductivity estimate. This procedure can identify lesion tissue conductivity with only a few percent error and guarantees source localization errors less than 5 mm.

Brain↗