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PubMed2001

Associated phoria and the measuring and correcting methodology after H.-J. Haase (MKH).

The test charts included in the Polatest, designed by H.-J. Haase and manufactured by Zeiss, are used in Germany, Switzerland and Scandinavia for prism correction of 'associated phoria.' From clinical experience with the Polatest Haase developed a motor and sensory theory of the different stages of decompensation of 'associated phoria ' and a strategy for its prismatic correction - the MKH (Measuring and Correcting Methodology after H.-J. Haase). The theory challenges many accepted ideas about the plasticity of the visual system and the use of prisms in the treatment of sensory abnormalities. This article, the first full description in English, describes and critically discusses the MKH.

Accommodation, Ocular↗
PubMed1997

Repeat measurement of case-control data: corrections for measurement error in a study of ischaemic stroke and haemostatic factors.

BACKGROUND: Haemostatic factors are suspected to be involved in the aetiology of cerebrovascular events. METHODS: In a case-control study of 105 cases of transient ischaemic attack and minor ischaemic stroke, and 241 controls, data were available on levels of the haemostatic factors-von Willebrand factor (vWF), plasminogen activator inhibitor-1 (PAI), tissue plasminogen activator (TPA) and factor VII (FVII). These are subject to measurement error and within-person fluctuation of true levels, which may bias relative risk estimates. For all subjects, two determinations were performed on the same blood sample, which allowed estimation of pure measurement error. For estimation of within-person fluctuation, levels were measured from a repeat blood sample on 81 of the controls one year later. RESULTS: The pure measurement error accounted for a very small proportion of the total variation in all cases. Uncorrected for within-person fluctuation, the odds ratio estimates associated with exceeding the median of vWF, PAI, TPA and FVII respectively were 1.88, 0.87, 1.30 and 0.93. After correction for within-person fluctuation odds ratios were 3.56, 0.80, 1.41 and 0.91. Because the PAI determination was not robust to storage conditions, it was estimated that 75% of the variation in this factor was within-person rather than between-persons. Thus, estimates of relative risk relation to PAI cannot be regarded as reliable in this study. CONCLUSIONS: It is likely that elevated levels of vWF are associated with increased risk of ischaemic stroke, but interpretation must be tentative, due to relatively large within-person fluctuation of vWF levels.

Analysis of Variance↗
PubMed1997

Measurement error correction for logistic regression models with an "alloyed gold standard".

Recently, some authors have questioned the validity of methods which correct relative risk estimates for measurement error and misclassification when the "gold standard" used to obtain information about the measurement error process is itself imperfect. When such an "alloyed" gold standard is used to validate the usual exposure measurement, the bias in the "regression calibration" (Rosner et al., Stat Med 1989; 8:1051-69) measurement-error correction factor for relative risks estimated from logistic regression models is derived. This quantity is a function of the correlations of the "alloyed" gold standard (X) and the usual exposure assessment method (Z) with the truth, of the ratio of the variances of X and Z, and of the correlation between the errors in the "alloyed" gold standard and the errors in the usual exposure assessment method. In this paper, it is proven that if the errors between Z and X are uncorrelated, the regression calibration method has no bias even when the gold standard is "alloyed." When a third method of exposure assessment is available and it is reasonable to assume that the errors in this method are uncorrelated with the errors in the other two exposure assessment methods, point and interval estimates of the correlation between the errors in X and Z are derived. These methods are illustrated here with data on the measurement of physical activity, vitamins A and E, and poly- and monounsaturated fat. In addition, when a third exposure assessment method is available, a modification of standard regression calibration is derived which can be used to calculate point and interval estimates of relative risk that are corrected for measurement error in both X and Z. This new method is illustrated here with data from the Health Professionals Follow-up Study, a study investigating the associations between physical activity and colon cancer incidence and between vitamin E intake and coronary heart disease. It is shown that in these examples, correlations of the errors in X and Z tended to be small. Even when moderate, estimates of relative risk corrected for error in both X and Z were not very different from the estimates which assumed that X was a true gold standard.

Bias↗
PubMed2006

Multiple-imputation for measurement-error correction.

BACKGROUND: There are many methods for measurement-error correction. These methods remain rarely used despite the ubiquity of measurement error. METHODS: Treating measurement error as a missing-data problem, the authors show how multiple-imputation for measurement-error (MIME) correction can be done using SAS software and evaluate the approach with a simulation experiment. RESULTS: Based on hypothetical data from a planned cohort study of 600 children with chronic kidney disease, the estimated hazard ratio for end-stage renal disease from the complete data was 2.0 [95% confidence limits (95% CL) 1.4, 2.8] and was reduced to 1.5 (95% CL 1.1, 2.1) using a misclassified exposure of low glomerular filtration rate at study entry (sensitivity of 0.9 and specificity of 0.7). The MIME correction hazard ratio was 2.0 (95% CL 1.2, 3.3), the regression calibration (RC) hazard ratio was 2.0 (95% CL 1.1, 3.7), and restriction to a 25% validation substudy yielded a hazard ratio of 2.0 (95% CL 1.0, 3.7). Based on Monte Carlo simulations across eight scenarios, MIME was approximately unbiased, had approximately correct coverage, and was sometimes more powerful than misclassified or RC analyses. Using root mean squared error as a criterion, the MIME bias correction is sometimes outweighed by added imprecision. CONCLUSION: The choice between MIME and RC depends on performance, ease, and objectives. The usefulness of MIME correction in specific applications will depend upon the sample size or the proportion validated. MIME correction may be valuable in interpreting imperfectly measured epidemiological data.

Bias↗
PubMed1983

Response time and percentage correct as measures of hearing aid performance.

A paradigm yielding response time and percentage correct data was implemented to assess the relative efficacy in differentiating subjects' performance between two disparate hearing aids. These aids represented high-frequency response (HFR) and conventional-frequency response (CFR) categories. Ten men with flat, moderate, sensorineural hearing losses were employed as subjects. The results revealed that (a) percentage correct measures did not differentiate between the two experimental aids, (b) response time measures did discriminate between the aids, and (c) response time data revealed superior performance with the CFR compared to the HFR instrument. Implementation of this method is advocated to increase the discriminating power of word recognition testing.

Acoustics↗
PubMed1997

Automatic measurement of corrected QT interval in Holter recordings: comparison of its dynamic behavior in patients after myocardial infarction with and without life-threatening arrhythmias.

This study was designed to determine the value of automatic corrected QT-interval measurement in Holter tapes in patients after myocardial infarction as a marker of life-threatening ventricular arrhythmias. We compared the corrected QT interval, automatically measured in 24-hour Holter recordings, in two groups of patients after myocardial infarction: group I was composed of 14 patients admitted consecutively to our hospital for documented sustained ventricular tachycardia or out-of-hospital cardiac arrest. Group II consisted of 28 patients with previous myocardial infarction with characteristics similar to those of group I, but without malignant ventricular arrhythmias in the follow-up. The global mean 24-hour corrected QT interval was longer in group I (425 +/- 20 msec) than in those patients after myocardial infarction without arrhythmias (group II) (405 +/- 17 msec; p < 0.01). Furthermore, a significant proportion of patients of group I (seven of 14) exhibited more peaks of corrected QT longer than 500 msec compared with patients of group II (two of 28; p < 0.005). A circadian rhythm of corrected QT peaks was observed in group I, having a significantly higher incidence from 11 PM to 11 AM (p < 0.05). We conclude that automatic corrected QT-interval measurement on Holter electrocardiogram is now available and feasible. Our results suggest that this is a marker for risk assessment of life-threatening ventricular arrhythmias. Large-scale trials are needed to confirm these results and to determine the predictive value of this technique for risk stratification.

Algorithms↗
PubMed2000

A simulation study of measurement error correction methods in logistic regression.

Measurement error models in logistic regression have received considerable theoretical interest over the past 10-15 years. In this paper, we present the results of a simulation study that compares four estimation methods: the so-called regression calibration method, probit maximum likelihood as an approximation to the logistic maximum likelihood, the exact maximum likelihood method based on a logistic model, and the naive estimator, which is the result of simply ignoring the fact that some of the explanatory variables are measured with error. We have compared the behavior of these methods in a simple, additive measurement error model. We show that, in this situation, the regression calibration method is a very good alternative to more mathematically sophisticated methods.

Calibration↗
PubMed1987

Direct determination of the attenuation coefficient for radionuclide volume measurements.

Correcting for the attenuation of photons between the cardiac chambers and chest surface is crucial for accurate nongeometric ventricular volume determinations from equilibrium radionuclide angiograms. Previous techniques have assumed that the attenuation coefficient of water for 99mTc (0.15/cm) should be used for this correction. In this study, this assumption was tested directly by measuring attenuation of the activity of a radioactive source within the right and left cardiac chambers. The balloon of a flow-directed catheter, filled with 99mTc, was used as a source and its depth within the body was measured with biplane fluoroscopy. In ten patients, a total of 36 measurements of attenuation were made. With linear regression analysis, the overall calculated attenuation coefficient, mu, was 0.12/cm (standard error of slope = 0.01, R = 0.93). Although the mean value of mu varied from 0.08 to 0.13 for four different intracardiac locations these differences were not significant. These direct measurements indicate that the attenuation of photons in the heart is not equivalent to that of water and suggest that an attenuation coefficient of 0.12/cm should be used in analyzing ventricular activity.

Adult↗
PubMed2004

[Measurement and correction of diagnostic X-ray spectra using a high resolution Schottky CdTe detector].

The purpose of this study is to measure diagnostic x-ray spectra using a high resolution Schottky CdTe detector (TOYO MEDIC RAMTEC 413A) and to determine the best response function of CdTe detector for correcting the measured spectra with using a rise time discrimination (RTD) circuit to primary x-ray spectra. Since the measured spectra were distorted by the response of CdTe detector and did not present the true photon spectra, the correction by the stripping procedure was applied. The response function of CdTe detector has been determined by using Monte Carlo simulation method for calculating the photon interaction (K-escape, coherent scattering and Compton scattering) and incomplete charge collection by trapping of hole and use of RTD circuit. This simulation performed with various important factors (mean path length lambda(h) of hole and weight factor W(q) of incomplete charge collection) for finding the best response function. The photon spectra corrected with those various response functions were compared with the corrected photon spectra measured using a high purity Ge (HP-Ge) detector (PRINCETON GAMMA-TECH NIGP1013345), and the Al-attenuation curves calculated from corrected spectra and measured using the HP-Ge detector were compared. The best-fitted response function was determined, and the attenuation curves calculated from the spectra corrected with this response function were agreed with that measured using the HP-Ge detector within maximum error 0.03 of the attenuation rate and 5.0 % of the half value layer.

Gamma Rays↗
PubMed2007

Interval estimation for rank correlation coefficients based on the probit transformation with extension to measurement error correction of correlated ranked data.

The Spearman (rho(s)) and Kendall (tau) rank correlation coefficient are routinely used as measures of association between non-normally distributed random variables. However, confidence limits for rho(s) are only available under the assumption of bivariate normality and for tau under the assumption of asymptotic normality of tau. In this paper, we introduce another approach for obtaining confidence limits for rho(s) or tau based on the arcsin transformation of sample probit score correlations. This approach is shown to be applicable for an arbitrary bivariate distribution. The arcsin-based estimators for rho(s) and tau (denoted by rho(s,a), tau(a)) are shown to have asymptotic relative efficiency (ARE) of 9/pi2 compared with the usual estimators rho(s) and tau when rho(s) and tau are, respectively, 0. In some nutritional applications, the Spearman rank correlation between nutrient intake as assessed by a reference instrument versus nutrient intake as assessed by a surrogate instrument is used as a measure of validity of the surrogate instrument. However, if only a single replicate (or a few replicates) are available for the reference instrument, then the estimated Spearman rank correlation will be downwardly biased due to measurement error. In this paper, we use the probit transformation as a tool for specifying an ANOVA-type model for replicate ranked data resulting in a point and interval estimate of a measurement error corrected rank correlation. This extends previous work by Rosner and Willett for obtaining point and interval estimates of measurement error corrected Pearson correlations.

Confidence Intervals↗
PubMed1985

Collagen implant in management of perlèche (angular cheilosis).

Perlèche (angular cheilosis) is often caused by the presence of saliva on skin adjacent to mucous membranes. In some cases saliva escapes from the mouth through deep grooves that extend inferolaterally from oral commissures. If the sulci are secondary to a decreased vertical dimension of the lower one third of the face (determined by described measurements), corrective dental measures may be curative. When this approach is not practical and in other cases when the grooves are produced by other causes, the defects can be corrected by use of injections of collagen implant. This has been done successfully in two patients, and angular cheilosis has not reoccurred.

Adult↗
PubMed2000

[Can fixation disparity be detected reliably by measurement and correctional techniques according H.J. Haase (MKH)?].

BACKGROUND: The theory of the "Measuring and Correction Methods of H.-J. Haase" (MCH) states that a small misalignment of one eye, called fixation disparity, indicates a difficulty in overcoming a "vergence position of rest" that is different from ortho position. This difficulty, so the theory, can cause asthenopic complaints, such as headaches, and these complaints can be relieved by prisms. The theory further claims that fixation disparity can be ascertained by a series of tests which depend on the subject's perception. The tests most decisive for the diagnosis of a so-called fixation disparity type 2 consist of stereo displays. The magnitude of the prism that allows the subject to see the test configurations in symmetry is thought to be the one that corrects the "vergence position of rest". METHODS: Nine subjects with healthy eyes in whom a "fixation disparity type 2" had been diagnosed were selected for the study. Misalignment of the eyes was determined according to the principle of the unilateral cover test. Targets identical for both eyes were presented on the screen of the Polatest E. Then, the target was deleted for one eye and the ensuing position change of the other eye was measured, using the search coil technique. This test was performed both with and without the MCH prism. RESULTS: In all 9 subjects the misalignment was less than 10 minutes of arc, i.e. in the range of normal fixation instability. Averaging across the 9 subjects, the deviation of the eye (misaligned according to MCH) was 0.79 +/- 3.45 minutes of arc in the direction opposed to that predicted by the MCH, a value not significantly different from zero. The MCH prism elicited a fusional vergence movement the magnitude of which corresponded to the magnitude of the MCH prism. CONCLUSION: Ascertaining fixation disparity with the MCH is unreliable. Accordingly, it appears dubious to correct a "vergence position of rest" on the basis of the MCH.

Adult↗
PubMed1997

Correcting for measurement error in the analysis of case-control data with repeated measurements of exposure.

The authors present a technique for correcting for exposure measurement error in the analysis of case-control data when subjects have a variable number of repeated measurements, and the average is used as the subject's measure of exposure. The true exposure as well as the measurement error are assumed to be normally distributed. The method transforms each subject's observed average by a factor which is a function of the measurement error parameters, prior to fitting the logistic regression model. The resulting logistic regression coefficient estimate based on the transformed average is corrected for error. A bootstrap method for obtaining confidence intervals for the true regression coefficient, which takes into account the variability due to estimation of the measurement error parameters, is also described. The method is applied to data from a nested case-control study of hormones and breast cancer.

Algorithms↗
PubMed2002

[Numerical simulation of dynamic characteristic of exhalation valve plate in pressure oxygen mask].

Objective. To find out the reason of "dithering" of exhalation valve plate in pressure oxygen mask under high overpressure condition. Method. Dynamic model of the exhalation valve plate in pressure oxygen mask was established. Aerodynamic force on the plate was determined by flowfield computing. The dynamic characteristic of the exhalation valve plate was analyzed by experimental measurement [correction of measurment] integrated with numerical simulation. Result. The movement of valve plate could be simulated with the method proposed, and the course of the"dithering" was found out. Conclusion. The "dithering" of the valve plate can be averted by cutting down the area of the film or increasing the diameter of the valve pedestal moderately.

Atmospheric Pressure↗
PubMed1998

[Continuous quality improvement in anesthesia].

Slow continuous quality improvement (SCQI) in anesthesia is a process that allows identification of problems and their causes. Implementing measures to correct them and continuous monitoring to ensure that the problems have been eliminated are necessary. The basic assumption of CQI is that the employees of an organization are competent and working to the best of their abilities. If problems occur they are the consequences of inadequacies in the process rather that in the individual. The CQI program is a dynamic but gradual system that invokes a slower rate of response in comparison with other quality methods, like quality assurance. Spectacular results following a system change are not to be expected an the ideal is slow and continuous improvement. A SCQI program was adapted by our department in May 1994, according to the recommendations of the American Society of Anesthesiologists. Problem identification was based on 65 clinical indicators, reflecting negative events related to anesthesia. Data were collected using a specially designed computer database. 4 events were identified as crossing previously established thresholds (hypertension, hypotension, hypoxia and inadequate nerve block). Statistical process control was used to establish stability of the system and whether negative events were influenced only by the common causes. The causes responsible for these negative events were identified using specific SCQI tools, such as control-charts, cause-effect diagrams and Pareto diagrams. Hypertension and inadequate nerve block were successfully managed. The implementation of corrective measures for the other events that cross the threshold is still in evolution. This program requires considerable dedication on the part of the staff, and it is hoped that it will improve our clinical performance.

Anesthesia↗
PubMed1992

[Legionella contamination in warm water systems of a large German city].

Since 1988 the Frankfurt City Health Department examined the hot water systems of all public indoor swimming pools, old age homes and hospitals, and made subsequent checks on the corrective measures introduced. In the 6 public indoor swimming pools the percentage of positive legionella findings, after corrective measures has dropped since 1988: at the central hot-water supply units from 47% to 23%, and at the peripheral tap connections from 66% to 22%. The number of negative samples rose from 43% to 77%. Thus the favourable effect of the corrective measures is demonstrated. Since 1988 samples have been taken from the shower water at old age homes. An increase in negative findings could be shown (from 58% to 70%). From 1990, however, an increase of high-level legionella contamination (> 10,000 Legionella colonies per litre) was detected as well. In one home with a generally high legionella contamination level (up to 75,000 legionella colonies per litre) an investigation of the legionella antibodies was done in the blood of 44 residents whose medical history included fever or bronchial symptoms. In no case a previous infection could be demonstrated. However, there was one patient with a definite legionella pneumonia in the home: this patient usually had been showering for at least 20 minutes a day. Legionella were found in the hot water systems of 16 of the 17 hospitals in Frankfurt. In 1991 more than half to the 204 samples were legionella positive. 5% of the samples had legionella contamination levels of more than 100,000 per litre. Corrective measures have been taken.(ABSTRACT TRUNCATED AT 250 WORDS)

Colony Count, Microbial↗