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At least 19 recordsLinked to original sources
PubMed2002

The performance of methods for correcting measurement error in case-control studies.

BACKGROUND: It is generally agreed that adjustment for measurement error (when feasible) can substantially increase the validity of epidemiologic analyses. Although a broad variety of methods for measurement error correction has been developed, application in practice is rare. One reason may be that little is known about the robustness of these methods against violations of their restrictive assumptions. METHODS: We carried out a simulation study to assess the performance of two error correction methods (a regression calibration method and a semiparametric approach) as compared with standard analyses without measurement error correction in case-control studies with internal validation data. Performance was assessed over a wide range of model parameters including varying degrees of violations of assumptions. RESULTS: In nearly all the settings assessed, the semiparametric estimate performed better than all alternatives under investigation. The regression calibration method is sensitive to violations of the assumptions of nondifferential error and small error variance. CONCLUSIONS: The semiparametric method is a very robust method to correct for measurement error in case-control studies, but lack of functional software hinders widespread use. If the assumptions for the regression calibration method are fulfilled, application of this method, originally developed for cohort studies, in case-control studies may be a useful alternative that is easy to implement.

Bias↗
PubMed1993

How reliable are chance-corrected measures of agreement?

Chance-corrected measures of agreement are prone to exhibit paradoxical and counter-intuitive results when used as measures of reliability. It is demonstrated that these problems arise with Cohen's kappa as well as with Aickin's alpha. They are the consequence of an analogy to Simpson's paradox in mixed populations. It is further shown that chance-corrected measures of agreement may yield misleading values for binary ratings. It is concluded that improvements in the design and the analysis of reliability studies are a prerequisite for valid and pertinent results.

Classification↗
PubMed1994

Chance-corrected measures of the validity of a binary diagnostic test.

Chance-corrected measures of the validity of diagnostic tests can be a valuable supplement to traditional measures which do not take chance-agreement between diagnostic test and true disease status into account. Recently, several authors have propagated chance-corrected measures of sensitivity and specificity, the most commonly employed indices of validity of binary diagnostic tests. A major limitation of these measures is their dependence on disease prevalence. In this paper, we propose simple alternative chance-corrected measures of sensitivity and specificity which do not share this limitation. The chance-corrected measure of sensitivity can be expressed as 1--negative likelihood ratio, and the chance-corrected measure of specificity can be expressed as 1--inverse of the positive likelihood ratio. The properties of the proposed measures are described and graphically illustrated, and formulas are given for point and interval estimation of the measures.

Models, Theoretical↗
PubMed1982

Corrective measures and occupational carcinogens.

The effectiveness of corrective measures in controlling occupational cancer has been related to present knowledge on proportion of cancer due to occupational exposure. The epidemiological background of such an estimate is analyzed with particular emphasis on the limits of the method. Different types of approach in cancer prevention and control in the industrial environment and their scientific background are reviewed. Some recent examples of the application of corrective measures in industries, which in the past presented a carcinogenic risk, are analyzed. The need for a multidisciplinary approach is emphasized.

Carcinogens, Environmental↗
PubMed2002

On the correct measurement of relative heavy charged particles to gamma thermoluminescent efficiencies.

In order to better understand the most important experimental aspects for performing correct measurements of relative thermoluminescent (TL) efficiencies, an investigation has been carried out to quantify the effect of using different experimental procedures in the evaluation of 3 MeV proton-to-gamma relative efficiency (etap,gamma) of LiF:Mg,Ti. Variations in batch, presentation, annealing and reader have been studied. When the same protocol is used to measure proton and gamma TL response, efficiency values obtained range from 0.36 to 0.59 for peak 5 and from 0.44 to 0.79 for the total signal. The use of different annealings and different batches leads to 20% and 10% differences in etap,gamma respectively. Large differences (40%) are found between efficiency values measured with TLD-100 chips and those obtained using TLD-100 microcubes. When 'mixed' procedures are used to measure the proton and the gamma response, differences in etap,gamma may increase even more. The main conclusion of this work is to stress the importance of measuring an entire series of experiments in the same laboratory with a carefully defined protocol and using dosemeters from the same batch to obtain heavy charged particle TL response and gamma TL response with identical annealing and readout procedures.

Fluorides↗
PubMed1999

Hair repair surgery. Corrective measures for improvement of older large-graft procedures and scalp scars.

BACKGROUND: Implanted hair follicles generally take and grow well. This can be desirable or undesirable, depending on the skill and aesthetic eye of the surgeon. Older methods employing larger grafts often produced pluggy, bristle brush, or "Barbie doll" hairlines that were unsightly and conspicuous. OBJECTIVE: Since patients possessing these outcomes often seek corrective measures, a search was undertaken to find effective, corrective repair methods. Unfortunately, relatively little has been published on this subject. METHODS AND RESULTS: Discussion will center on recipient site repair, donor site repair, and scar repair. Recipient sites can be improved with a combination of laser ablation, electrolysis, punch removal, and fill-in micrografting. Donor sites can be improved by reexcision, undermining, tissue expansion, and layered closure. Anterior scalp scars may be improved by punch excision and micrografting. CONCLUSIONS: Satisfactory improvement for untoward hair transplantation outcomes may be obtained with one or more corrective procedures in many patients.

Cicatrix↗
PubMed2001

Necessary precautions in measuring correct vertical jumping height by means of force plate measurements.

The present study was designed to investigate the determination of vertical jumping height by means of force plate measurements. Four different sources of error influence this determination: the measurement of body mass, the determination of take off, the integration frequency, and the assessment of the initial conditions influencing the determination of the start of the movement. A theoretical model was utilized to simulate the vertical ground reaction forces in vertical jumping and to compare the outcome of analytical and numerical double integration of the vertical acceleration of the body centre of mass. A high integration frequency and an optimizing loop for body mass determination were found to be important and should be taken into account when determining jumping height parameters.

Acceleration↗
PubMed2001

[Pharmacologic interactions in chronic treatments: corrective measures for its prevention in a basic area of rural health].

OBJECTIVES: To identify the pharmacological interactions of clinical relevance (PICR) in the medication authorization cards (MAC) of the chronically ill and to establish strategies to minimise their appearance. DESIGN: Cross-sectional descriptive study. SETTING: Rural primary care centre. PATIENTS: Random sample of 626 MAC out of a total of 1306. MEASUREMENTS AND MAIN RESULTS: In December 1998, the following was gathered for every MAC with more than one drug treatment: age, sex, number of drugs, intrinsic value, drugs prescribed, daily dose and pharmacological interactions (PI), classified (using the scale of Hansten 1996) into light and clinically relevant. STATISTICAL ANALYSIS: Mantel-Haenszel (alpha = 0.05). Patients' mean age was 69.1 (95% CI, +/- 1.2). Mean number of drugs per MAC was 4 (95% CI, +/- 0.2). 341 PI affecting 197 patients (31.5%, 95% CI, +/- 3.6) were identified. 24.9% (95% CI, +/- 4.5) were PICR, detected in 11.7% (95% CI, +/- 2.5) of the MAC. The existence of PI was related to the number of drugs prescribed to each patient (p < 0.01). There were 26 PI with drugs of low intrinsic value (7.6%; 95% CI, +/- 2.8). 74.1% (95% CI, +/- 9.3) of the total PICR could be avoided by simple recommendations; and the remaining 25.9% (95% CI, +/- 9.3) by monitoring and follow-up of patients. CONCLUSIONS: It is important to identify the medications most commonly involved in the PICR so as to establish corrective measures to minimise the risks arising from multiple medication. Four educational messages advise on over 60% of the PICR detected.

Aged↗
PubMed1983

[Corrective measures following imperfectly healed fractures].

An overview of forms and localization of falsely healed fractures and possibilities for their correction is presented. In contrast to statically loaded lower limbs, posttraumatic arthrosis due to false position of the upper limbs is less common. In these cases indication for corrective osteotomy is aimed above all at improving the limb function. Central restorative measures are corrective osteotomy following falsely healed supracondylar humerus fractures in childhood and open wedge osteotomy of distal radius fractures. Even minimal axial deviations in the lower limbs will lead to false loading of joint surfaces and to early arthrosis, thus corrective osteotomy is indicated at a much earlier stage.

Adolescent↗
PubMedDate not supplied

A new look at displacement factor and point of measurement corrections in ionization chamber dosimetry.

A new technique is presented for determination of the effective point of measurement when cavity ionization chambers are used to measure the absorbed dose due to ionizing radiation in a dense medium. An algorithm is derived relating the effective point of measurement to the displacement correction factor. This algorithm relates variations of the displacement factor to the radiation field gradient. The technique is applied to derive the magnitudes of the corrections for several chambers in a p(66)Be(49) neutron therapy beam.

Mathematics↗
PubMed2002

[Prophylactic and correctional measures for thromboembolic complications in performance of the upper extremity replantation and microvascular autotransplantation of combined complex of tissues].

There were analyzed the causes and factors, influencing the thromboembolic complications frequency, in performance of the upper extremity segment replantation in 220 injured persons and of microsurgical the tissues defect plasty using combined complex of tissues (CCT)--in 154 patients. The role of anticoagulational therapy in complex of remedial measures, directed on the occurrence prophylaxis and medicinal correction of hemodynamic disorders in microvascular anastomoses after the operation, was determined. The advantages of low-molecular weight heparin (Fraxiparine) administration in comparison with the standard heparinotherapy were showed: lowering of thromboembolic and hemorrhagic complications occurrence frequency, the unique method of Fraxiparine subcutaneous injection into the replanted segment and CCT was presented.

Adolescent↗
PubMedDate not supplied

Corrective measures for myopia.

Many myopic people, expressing dissatisfaction with traditional methods of optical correction, are interested in a permanent correction of their refractive error which would alleviate dependence on corrective lenses. Although much effort has been put forth in the last century, there is still no method of correcting myopia which is broadly acceptable as safe and effective. The nonsurgical procedures of orthokeratology and the topical use of cycloplegics have not been well proven. Surgical measures are the current vectors of hope. Surgical procedures on parts of the eye other than the cornea have proven to be difficult. Surgery which alters the refractive power of the cornea (refractive keratoplasty) has been used frequently in the past decade. These procedures include keratomileusis, epikeratophakia and radial keratotomy. The latter is currently the most often performed method for the correction of myopia. This paper critiques the major methods, explains their historical development and basic procedures, lists major published studies and discusses their problems and promise for their future.

Contact Lenses↗
PubMed1997

Is there a gain from "chance-corrected" measures of diagnostic validity?

Several authors have proposed alternatives to sensitivity and specificity which they recommend as so-called "chance-corrected" versions of these parameters of diagnostic validity. We argue that these new measures have some undesirable properties in comparison with the established measures and no substantial advantages. In particular, the extension of this concept to chance-corrected ROC curves is shown to be less useful than classical ROC analysis.

Diagnosis↗
PubMed1984

[Post-traumatic growth disorders and corrective measures on the growing skeleton].

In order to develop efficient therapies in paediatric traumatology we investigated 1500 patients in all age groups with bony lesions of the growing skeleton. In particular we wanted to evaluate the limits and reliability of the correction mechanisms. Having done this evaluation we found some completely new correction mechanisms, and also we defined the reliability of the known mechanisms of repair. Also we wanted to determine the frequencies of the various disturbances of growth and how far these could be influenced by primary therapy. The rare disturbance of partial stimulation of growth, resulting in consecutive deformity was the only one which could be primarily influenced by therapy.

Child↗
PubMed1988

Modification in Ramsay's method for correct measurement of total iron-binding capacity.

Lack of satisfactory literature evidence and experiences with results of quality control assessment trials in The Netherlands prompted reconsideration of the determination of total iron-binding capacity (TIBC) in human and control sera. It was found that for a correct determination of serum TIBC the Fe(III)-saturating reagent must be able to correct an abnormally high serum pH due to a subnormal CO2 content of the sample. Such low CO2 contents are frequently found in reconstituted quality control sera. Detailed studies on combinations of mixtures of serum with varying pH and Fe(III)-saturating solutions with increasing amounts of added acid revealed a linear equation of the minimum amount of acid needed in relation to the original serum pH.

Carbon Dioxide↗
PubMedDate not supplied

[Correction measured by attenuation in tomographic heart studies with single photon emission with thallium 201. Comparison with positron- emission tomographic studies with ammonium marked with nitrogen].

PURPOSE: We investigated 201Tl myocardial uptake with(out) nonuniform attenuation compensation in ischemic myocardiopathy patients. The segmental patterns of the two types of SPECT images were compared with PET [13N]NH3 studies performed in the same patient. PET images were taken as reference and the diagnostic accuracy of SPECT with(out) attenuation correction was evaluated. MATERIAL AND METHODS: During the SPECT study transmission and emission data were simultaneously recorded by a triple head gamma camera equipped with fan beam collimators and a 99mTc transmission line source (740MBq). SPECT and PET images, the former reconstructed with(out) attenuation correction, were corecorded and reoriented along the short axis. The left ventricular wall was divided into 11 segments and segmental activity normalized to maximum in each study. RESULTS: Statistically significant differences were found between PET/(un)corrected SPECT ratios in posterior and septal segments. In these myocardial regions, attenuation correction compensates for attenuation artifacts, by correcting the underestimation of radioactivity concentration caused by radiation absorption. A statistically significant difference was also found in midventricular anterior and apical segments (p < .05). However, in these regions attenuation correction results in a decrease in corrected relative to uncorrected SPECT activity. The agreement rate with PET data is higher for corrected SPECT (mean differences were 3.12 +/- 11.51 and 2.19 +/- 8.63 for uncorrected versus corrected SPET). We had 50% positive and 77% negative predictive value without attenuation correction, versus up to 69% and 90%, respectively, with attenuation correction. CONCLUSIONS: The attenuation correction procedure with simultaneous transmission-emission effectively reduces attenuation artifacts in SPECT myocardial imaging. While diagnostic accuracy increases in posterior and septal myocardial regions, anterior and apical data need careful interpretation because a relative decrease in radioactivity concentration can be observed after attenuation correction.

Adult↗
PubMed1985

Acute responses to phosgene inhalation and selected corrective measures (including surfactant).

We exposed 22 mongrel dogs to 94 ppm phosgene for 20 min from a non-rebreathing system. We expressed exposure to phosgene as ppm X VI X min X kg 1, i.e., the amount of gas containing a known phosgene concentration that was actually inhaled per min standardized to body weight, the "exposure index" (EI). In contrast, the conventional expression of exposure, i.e., ppm X min, fails to take volume inhaled (VI) and body weight into account. Five dogs received no intervention and served as controls. Fourteen dogs received basic therapy of oral cortisone (40 mg/kg) and NaHCO3 (3 mEq/kg) plus 100% O2 (FiO2 = 1.0) for 30 min after the exposure period. These animals were further divided according to the following selected additional therapies, which were started 30 min after exposure: Theophylline, 5 mg/kg iv for 20 min followed by 1 mg/kg/hr for 70 min (n = 5). Three dogs of this group were given a trial of 5 cm H2O expiratory resistance during the period of basic therapy. Because of the untoward response, expiratory resistance was discontinued and not used in other experiments. PGE2-hi, [1 microgram/kg/min] iv for 90 min (n = 3). PGE1-lo, [0.04 microgram/kg/min] iv for 90 min (n = 3). Atropine, 0.5 mg/kg iv at 30 and 50 min after exposure (n = 3). Three dogs [group 5] received oral cortisone and NaHCO3 plus inhaled supplementary surfactant, 2.7 mg/min ultrasonically nebulized (FiO2 = 0.5; phosphate buffer), for 30 min after exposure. All treated dogs, groups [1] through [4] and the surfactant group [5], received cortisone (40 mg/kg/hr iv), NaHCO3 to correct base deficit, and O2 to correct hypoxemia from 30 min to 120 min after exposure. Because of its clearly beneficial effect in group [1], theophylline was also given to all other treatment groups during this period. At the end of the study, all lungs were excised, examined and prepared for light microscopy. We found that EI, which varied among subjects because of spontaneous variations of VI during exposure, correlated significantly with the changes in base deficit induced by phosgene inhalation. We also found that the change in minute ventilation, delta VI X kg-1, correlated significantly with changes in lung compliance, peak flow and base deficit. Evaluation of the various therapeutic modalities revealed the following: Immediate therapy with O2 is vital and and FiO2 of 0.4 to 0.5 is sufficient.(ABSTRACT TRUNCATED AT 400 WORDS)

Administration, Intranasal↗