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PubMed1994

A review of the role of Epidemiology and the use of indices in periodontal research.

In this review paper, the role of epidemiological research is discussed, with particular regard to periodontal diseases. The different forms of observational epidemiological study are explained and general sources of error related to all such studies and specific sources of error related to each particular type of study are considered. The qualities of an ideal epidemiological index are listed and indices used in periodontal research are discussed in the context of the parameters they set out to assess. General considerations relating to the use of index systems in clinical practice are highlighted.

Case-Control Studies↗
PubMed2001

Interpreting epidemiological research: blinded comparison of methods used to estimate the prevalence of inherited mutations in BRCA1.

While sequence analysis is considered by many to be the most sensitive method of detecting unknown mutations in large genes such as BRCA1, most published estimates of the prevalence of mutations in this gene have been derived from studies that have used other methods of gene analysis. In order to determine the relative sensitivity of techniques that are widely used in research on BRCA1, a set of blinded samples containing 58 distinct mutations were analysed by four separate laboratories. Each used one of the following methods: single strand conformational polymorphism analysis (SSCP), conformation sensitive gel electrophoresis (CSGE), two dimensional gene scanning (TDGS), and denaturing high performance liquid chromatography (DHPLC). Only the laboratory using DHPLC correctly identified each of the mutations. The laboratory using TDGS correctly identified 91% of the mutations but produced three apparent false positive results. The laboratories using SSCP and CSGE detected abnormal migration for 72% and 76% of the mutations, respectively, but subsequently confirmed and reported only 65% and 60% of mutations, respectively. False negatives therefore resulted not only from failure of the techniques to distinguish wild type from mutant, but also from failure to confirm the mutation by sequence analysis as well as from human errors leading to misreporting of results. These findings characterise sources of error in commonly used methods of mutation detection that should be addressed by laboratories using these methods. Based upon sources of error identified in this comparison, it is likely that mutations in BRCA1 and BRCA2 are more prevalent than some studies have previously reported. The findings of this comparison provide a basis for interpreting studies of mutations in susceptibility genes across many inherited cancer syndromes.

Chromatography, High Pressure Liquid↗
PubMed2000

Errors in ultrasound digital image distance measurements.

Digital image distance measurements have two sources of error: they are the inherent image pixelation error and modality-specific registration errors. A theoretical analysis was performed to determine the pixelation error uncertainty in ultrasound (US) clinical and phantom digital image distance measurements. For horizontal or vertical phantom image distance measurements, the average absolute image pixelation error was found to be 0.5 pixel width. In the clinical horizontal case, the combined absolute distance measurement error due to pixel size and operator cursor placement errors was found to be 1.5 pixel widths (for a cursor placement error of 1 pixel width). For image clinical distance measurements, a formula is given for the dependence of the measurement error on the inclination of the measured structure in the pixel matrix. A protocol is recommended that minimizes all sources of error in clinical image distance measurements.

Humans↗
PubMed2002

Reliability of cough effort intensity assessment by nurses.

This study examines the dependability of naïve nursing assessments of cough effort intensity (CEI) in unstable, but realistic, clinical situations. Sixty-two medical and surgical patients were recruited while on mechanical ventilation and studied on 3 consecutive days. Each day, three nurses measured two CEI ratings 3 minutes apart. Using a generalizability theory approach, the researchers estimated multiple sources of error in the measurement of CEI. Patient and day of measurement represented systematic variance, planned to increase variability in CEI. Time of assessment and nurse rater represented random sources of error. The design accounted for all sources of measurement error in the model. Variability in CEI was accounted for by individual patient differences and raters nested within patient day. The dependability coefficient was .39. Thus, the investigators concluded that naïve nurse assessments of CEI are undependable in clinical situations.

Adult↗
PubMed1998

Measurement of intraoperative brain surface deformation under a craniotomy.

OBJECTIVE: Several causes of spatial inaccuracies in image-guided surgery have been carefully studied and documented for several systems. These include error in identifying the external features used for registration, geometrical distortion in the preoperative images, and error in tracking the surgical instruments. Another potentially important source of error is brain deformation between the time of imaging and the time of surgery or during surgery. In this study, we measured the deformation of the dura and brain surfaces between the time of imaging and the start of surgical resection for 21 patients. METHODS: All patients underwent intraoperative functional mapping, allowing us to measure brain surface motion at two times that were separated by nearly an hour after opening the dura but before performing resection. The positions of the dura and brain surfaces were recorded and transformed to the coordinate space of a preoperative magnetic resonance image, using the Acustar surgical navigation system (manufactured by Johnson & Johnson Professional, Inc., Randolph, MA) (the Acustar trademark and associated intellectual property rights are now owned by Picker International, Highland Heights, OH). This system performs image registration with bone-implanted markers and tracks a surgical probe by optical triangulation. RESULTS: The mean displacements of the dura and the first and second brain surfaces were 1.2, 4.4, and 5.6 mm, respectively, with corresponding mean volume reductions under the craniotomy of 6, 22, and 29 cc. The maximum displacement was greater than 10 mm in approximately one-third of the patients for the first brain surface measurement and one-half of the patients for the second. In all cases, the direction of brain shift corresponded to a "sinking" of the brain intraoperatively, compared with its preoperative position. Analysis of the measurement error revealed that its magnitude was approximately 1 to 2 mm. We observed two different patterns of the brain surface deformation field, depending on the inclination of the craniotomy with respect to gravity. Separate measurements of brain deformation within the closed cranium caused by changes in patient head orientation with respect to gravity suggested that less than 1 mm of the brain shift recorded intraoperatively could have resulted from the change in patient orientation between the time of imaging and the time of surgery. CONCLUSION: These results suggest that intraoperative brain deformation is an important source of error that needs to be considered when using surgical navigation systems.

Adult↗
PubMed1990

[Importance of diagnosis and preoperative care of the conjunctiva].

The conjunctival smear is an important part of preoperative diagnosis. Although the method is very easy there are many possible sources of error. The validity of smear results was studied; the sources of error are discussed in the present paper. The different bacterial flora of the conjunctival sac and the lid margin were investigated. It was shown that eye drop dispensers become contaminated during use. The use of single-dose Ophtiolen has the advantage--in addition to improved hygiene, that no stabilizing agents are used. Preoperative efforts to achieve asepsis have to be continued during the operation. A new adhesive tape specially developed for ophthalmic surgery has been found very effective. This new tape is described.

Anti-Bacterial Agents↗
PubMedDate not supplied

Use of a modified nominal group process for improving laboratory performance in human immunodeficiency virus type 1 antibody testing. Reaching consensus on three questions concerning HIV-1 testing.

Using expert panels of medical technologists and public health microbiologists, a modified nominal group process was used to reach a consensus on three questions concerning current human immunodeficiency virus type 1 (HIV-1) testing methods. The questions related to important sources of error, improving the testing process, and improving proficiency testing. The modified nominal group process proved to be effective in developing lists of errors in laboratory testing; it provided a fast, economic means of identifying possible areas for improving laboratory quality assurance and training programs. For the HIV testing model, the focus group panelists indicated laboratory pipetting errors, labeling, and specimen identification as the most important sources of error. To improve the quality of this testing, the panel recommended standardizing test interpretation and restricting testing to laboratories licensed to perform HIV-1 testing. To improve proficiency testing, the use of blind specimens and establishing minimum standards of performance were suggested.

California↗
PubMed2000

Accuracy of EEG dipole source localisation in presence of brain lesions.

Inverse solution techniques based on electroencephalographic (EEG) measurements are a powerful mean of gaining knowledge about brain functioning, being used to estimate location, orientation and strength of neural electrical sources of brain activity. A model of the head, a model of the source and an electric-field computational method are necessary to describe the EEG problem mathematically. Volume conductor models commonly used to describe the EEG neglect the presence of brain lesions. We evaluated the need of considering brain lesions in head models for precise mapping of neural activity nearby the lesion, as it is requested for neurosurgical preoperative planning. A systematic evaluation of the effects of neglecting brain lesions in EEG dipole source localisation accuracy has been performed by computer simulations for different pathologic conditions, source types and source positions. Simulations of EEG measurements were carried out using a modified eccentric-spheres model of the head in which an eccentric bubble approximates effects of actual brain lesions. A three concentric spheres model has been used in the inverse dipole fitting procedure to quantify source localisation errors caused by ignoring the presence of lesions in the head model. 64 different situations have been analysed. Source reconstruction errors resulted negligible only for some relative positions of source, lesion and electrodes. The largest errors, up to 2.5 cm, have been found for a lesion placed between source and electrodes and for a source internal to the lesion (not circumscribed tumours). We conclude that source localisation process is largely affected by a nearby lesion and thus electrical mapping of brain activity must be performed embedding brain lesions in the head model.

Brain Diseases↗
PubMed1995

Three new residual error models for population PK/PD analyses.

Residual error models, traditionally used in population pharmacokinetic analyses, have been developed as if all sources of error have properties similar to those of assay error. Since assay error often is only a minor part of the difference between predicted and observed concentrations, other sources, with potentially other properties, should be considered. We have simulated three complex error structures. The first model acknowledges two separate sources of residual error, replication error plus pure residual (assay) error. Simulation results for this case suggest that ignoring these separate sources of error does not adversely affect parameter estimates. The second model allows serially correlated errors, as may occur with structural model misspecification. Ignoring this error structure leads to biased random-effect parameter estimates. A simple autocorrelation model, where the correlation between two errors is assumed to decrease exponentially with the time between them, provides more accurate estimates of the variability parameters in this case. The third model allows time-dependent error magnitude. This may be caused, for example, by inaccurate sample timing. A time-constant error model fit to time-varying error data can lead to bias in all population parameter estimates. A simple two-step time-dependent error model is sufficient to improve parameter estimates, even when the true time dependence is more complex. Using a real data set, we also illustrate the use of the different error models to facilitate the model building process, to provide information about error sources, and to provide more accurate parameter estimates.

Models, Theoretical↗
PubMed1998

A quality assurance test tool for high dose-rate remote afterloading brachytherapy units.

A QA test tool is designed to quantitatively measure the HDR source positioning error, and to facilitate quick and dependable HDR timer linearity test and daily output constancy check. The test tool consists of two concentric disks. The lower disk has a cutout for inserting an HDR catheter, and the upper disk accepts a diode or miniature ionization chamber and can rotate relative to the lower disk. Ionization readings from the source (transferred to the center of the disks) are obtained at two rotational positions of the upper disk which houses the detector. The ratio of the readings is used to determine the source-positioning error of the HDR unit relative to the nominal source position by a simple triangulation principle. Experimental measurements confirm that the QA test tool is sensitive to approximately 0.2 mm variance in source positioning errors. In addition, the QA test tool is suitable for other common HDR QA tests such as the source travel step size test, the daily HDR unit output constancy check, and the timer linearity test. Its simple and robust design permits routine clinical use and provides a high confidence level in the accurate operation of HDR units.

Biophysical Phenomena↗
PubMed2005

Effects of corneal thickness, curvature, astigmatism and direction of gaze on Goldmann applanation tonometry readings.

BACKGROUND: The aim of this study was to evaluate the impact of various sources of error in Goldmann applanation tonometry (GAT). OBJECTIVES: We evaluated the effect of corneal thickness, curvature, astigmatism and direction of gaze as sources of error in GAT. METHODS: Orbscan-II (Bausch & Lomb, Inc., Rochester, N.Y., USA) examinations were made on 30 healthy subjects and 9 keratoconus patients, and the intraocular pressure (IOP) was measured with GAT centrally, temporally and inferiorly, with the tonometer prism set horizontally and vertically. Orbscan-II images from 50 younger subjects and 49 older subjects were analysed retrospectively. RESULTS: IOP was lower on nasal gaze (p = 0.009) but higher on upward gaze (p < 0.001) compared with forward gaze. IOP and the corneal thickness were independently correlated (R(2) = 0.04; p = 0.003), as were the difference in astigmatic vector in the horizontal and vertical meridians and the difference in IOP measured with a horizontal and vertical prism (R(2) = 0.17; p < 0.001). No correlation between IOP and corneal curvature was found. In the keratoconus patients, IOPs were generally low, with large astigmatic differences. CONCLUSIONS: Corneal thickness, astigmatism and direction of gaze are clinically important sources of error in GAT. IOP should preferably be measured with the prism both horizontally and vertically. If only one direction is chosen, a vertical prism is less sensitive to different directions of gaze. Direction of gaze should be carefully monitored, especially in an irregular cornea.

Adult↗
PubMed2005

Source monitoring for actions in hallucination proneness.

INTRODUCTION: In the present study we explored the role of cognitive factors in hallucinatory proneness by utilising an incidental source monitoring task consisting of actions. METHOD: A total of 65 normal subjects were administered a source monitoring task and were asked either to: (1) perform the action; (2) watch the experimenter perform the action; (3) imagine him/herself performing the action; (4) imagine the experimenter performing the action; (5) or listen to the experimenter say the action verbally. Following a delay, actions were presented consisting of those already presented in one of the 5 conditions (old), and those never before presented (new). For each action, subjects were required to identify if the action was old or new. If the action was identified as old, subjects were required to identify the source of the word (i.e., one of the 5 conditions). Subjects also completed a questionnaire assessing metacognitive beliefs. Subjects were grouped according to their scores on a revised and elaborated version of the Launay-Slade Hallucinations Scale (LSHS). Those with scores within the top 25% were included in the hallucination-prone group (HP) (n = 16), whereas scores within the lower 25% were included in the nonhallucination-prone group (NHP) (n = 16). RESULTS: Within the internal conditions, hallucination-prone subjects confused two internal sources (a specific internal-internal source discrimination error). That is, for imagined actions where the subjects performed the action, HP subjects erroneously attributed these towards an imagined action performed by the experimenter. Results also revealed that hallucination-proneness was associated with metacognitive beliefs. Finally, there was a significant relation between certain metacognitive beliefs and the internal-internal source discrimination error on the source monitoring task. CONCLUSIONS: Findings from the present study suggest that an important cognitive deficit in the genesis of hallucinations may be a perturbation in the control of internally generated cognitive events.

Journal Article↗
PubMed2005

Analysis of the errors in explicitly correlated electronic structure theory.

The explicitly correlated second order Møller-Plesset (MP2-R12) methods perform well in reproducing the last detail of the correlation cusp, allowing higher accuracy than can be accessed through conventional means. Nevertheless in basis sets that are practical for calculations on larger systems (i.e., around triple- or perhaps quadruple-zeta) MP2-R12 fails to bridge the divide between conventional MP2 and the MP2 basis set limit. In this contribution we analyse the sources of error in MP2-R12 calculations in such basis sets. We conclude that the main source of error is the choice of the correlation factor r12. Sources of error that must be avoided for accurate quantum chemistry include the neglect of exchange commutators and the extended Brillouin condition. The generalized Brillouin condition is found not to lead to significant errors.

Algorithms↗
PubMed2003

A reassessment of normal cervical range of motion.

STUDY DESIGN: Intraexaminer and interexaminer/procedure reliability and error analysis using a repeated-measures design. OBJECTIVE: To quantify sources of discrepancies in cervical range of motion values between two procedures that use the same potentiometric technology. SUMMARY OF BACKGROUND DATA: Studies using an early version of an electrogoniometer system, which was connected between a helmet worn by the study participant and a chair on which they sat, reported unusually high values for active and passive cervical range of motion, although measurements were reliable. To understand the sources of the discrepancies between that study and later studies (using upgraded software), the current study was designed to quantify possible sources of error contributed by various components of the procedures: helmet, thoracic reference, chair, and software. METHODS: A total of 22 asymptomatic study participants were evaluated in two separate sessions, 1-3 days apart. Components of two procedures were changed systematically in a series of repeated measurements to provide concurrent reliability and to assess sources of error between the two procedures. RESULTS: The reliabilities of both procedures were generally high with no systematic trends, except for lower values for flexion-extension studies with Procedure 2. Procedure 2 also provided systematically greater range of motion values (2-8 degrees ) than Procedure 1, except for flexion (half-cycle). The source of the greatest discrepancy between the two procedures was the software, when comparing the original with the updated versions. With regard to the instrumentation, the greatest source of variability was in the thoracic reference post; next was the helmet, and least significant was the type of seat used. A comparison of overall procedure discrepancies and summation of individual elements of the procedures accounted for virtually all of the observed error. CONCLUSION: The potentiometer-based electrogoniometer is a reliable instrument for determining cervical range of motion. Measurements appear to be more valid when the thoracic reference point is physically attached to the study participant's body. The original software provided with the system appears to have contributed to systematic overestimation of ranges of motion, but current units provide measurements that are both reliable and valid.

Adult↗
PubMed1996

The application of echo-tracking methods to endothelium-dependent vasoreactivity and arterial compliance measurements.

Measurements of endothelium-dependent vasoreactivity and arterial compliance are important metrics of vascular pathophysiology which may be used for the development and evaluation of therapeutic methods. The technique of ultrasonic echo tracking is applicable to measurements of endothelium-dependent vasoreactivity and arterial compliance. To evaluate the application of echo tracking to these measurements, we constructed a system based upon analog-to-digital conversion and storage of the radio frequency (RF) ultrasound signals. Off-line analysis of the RF data with various echo-tracking algorithms demonstrated two potential sources of error: tracking drift and RF transition regions. The tracking drift resulted from the slow accumulation of tracking error. The RF transition regions were associated with disparate motions of neighboring reflectors or the insonation of a new series of tissue layers. As a result of these sources of error, the application of echo tracking to endothelium-dependent vasoreactivity measurements is unlikely to outperform duplex ultrasound methods. The application of echo tracking to arterial compliance measurements via the arterial pressure/diameter relationship may produce variable results due to RF transition regions. Finally, the application of echo tracking to arterial compliance measurements via the pulse wave velocity is relatively insensitive to these sources of error because the pulse-wave velocity measurement depends upon the timing of the peak arterial distension, not on the absolute value of the distension.

Algorithms↗
PubMed1991

Instrumentation, principles, and pitfalls of ultrasonography.

Diagnostic ultrasonography has had a major impact on clinical diagnosis in veterinary medicine. Improved instrumentation (increased resolution and reliability) and ease of operation resulted in acceptance of ultrasonography as a diagnostic tool in private practice. As with any new imaging modality, sources of error exist. Operator inexperience and "overdiagnosis" of the image are major sources of error in the early stages of ultrasound training. The ultrasound examination of the animal should always be evaluated in conjunction with the history, physical examination, and other laboratory findings. Errors in interpretation most often occur when the ultrasound image is evaluated without respect to this complete data base. It must be stressed that ultrasonography does not replace, but is a valuable adjunct to, plain-film radiography.

Animals↗
PubMed2005

Anatomic pathology databases and patient safety.

CONTEXT: The utility of anatomic pathology discrepancies has not been rigorously studied. OBJECTIVE: To outline how databases may be used to study anatomic pathology patient safety. DESIGN: The Agency for Healthcare Research and Quality funded the creation of a national anatomic pathology errors database to establish benchmarks for error frequency. The database is used to track more frequent errors and errors that result in more serious harm, in order to design quality improvement interventions intended to reduce these types of errors. In the first year of funding, 4 institutions (University of Pittsburgh, Henry Ford Hospital, University of Iowa, and Western Pennsylvania Hospital) reported cytologic-histologic correlation error data after standardizing correlation methods. Root cause analysis was performed to determine sources of error, and error reduction plans were implemented. PARTICIPANTS: Four institutions self-reported anatomic pathology error data. MAIN OUTCOME MEASURES: Frequency of cytologic-histologic correlation error, case type, cause of error (sampling or interpretation), and effect of error on patient outcome (ie, no harm, near miss, and harm). RESULTS: The institutional gynecologic cytologic-histologic correlation error frequency ranged from 0.17% to 0.63%, using the denominator of all Papanicolaou tests. Based on the nongynecologic cytologic-histologic correlation data, the specimen sites with the highest discrepancy frequency (by project site) were lung (ranging from 16.5% to 62.3% of all errors) and urinary bladder (ranging from 4.4% to 25.0%). Most errors detected by the gynecologic cytologic-histologic correlation process were no-harm events (ranging from 10.7% to 43.2% by project site). Root cause analysis identified sources of error on both the clinical and pathology sides of the process, and error intervention programs are currently being implemented to improve patient safety. CONCLUSIONS: A multi-institutional anatomic pathology error database may be used to benchmark practices and target specific high-frequency errors or errors with high clinical impact. These error reduction programs have national import.

Benchmarking↗
PubMed1984

Seroepidemiology of schistosomiasis japonica by ELISA in the Philippines. II. Unreliability of stool examination in the measurement of incidence.

It was shown in a previous study that a single quantitative stool examination (by technics currently used in the Philippines) is so sensitive that it underestimated by 50% the prevalence of schistosomiasis japonica in children detected by a single serologic assay (ELISA). This paper proves that measurement of incidence of the infection among these same children by stool examination is unreliable as well. Three important sources of error in the measurement of incidence by stool examination are: (a) the inclusion of already infected children in the group of presumably uninfected children in which conversion (change from negative to positive) is being measured; (b) the insensitivity of stool examination in identifying those who do acquire infection among the initially uninfected; and (c) spontaneous, possibly temporary, stool reversion. An overestimation of incidence results from error (a) because already infected children have 5-7 times the tendency to convert than do uninfected children; error (b) tends to produce an underestimation of incidence since stool examination will detect only about one-half of the children who do become infected; while error (c) also tends to cause an underestimation of incidence and is dependent on the frequency of stool examinations--34% of the conversions observed by multiple examinations may not be detected in a single year-end examination. The equivalent sources of error are insignificant when ELISA is employed to measure incidence. In the 3 years of observation, the annual incidence of schistosomiasis japonica measured by ELISA showed no significant change (13.5%, 16.7%, and 15.6%); on the other hand, the annual incidence measured by stool examination showed a significant reduction from 37.5% down to 16.0% and 15.1%. Significant sources of error invalidate measurements by stool examination; it is therefore concluded that incidence measurements have failed to produce acceptable evidence of reduction in transmission in the area of study in the 3 years of control operations. We believe that insistence on relying almost exclusively on the parasitologic technic can result in an erroneous evaluation of the control program currently being implemented.

Antibodies↗