Step Calibration Research Articles

Rasch Analysis of the Daily Living Tasks Dependent on Vision (DLTV)

To examine internal consistency, refine the response scale, and obtain a linear scoring system for the visual function instrument, the Daily Living Tasks Dependent on Vision (DLTV). Data were available from 186 participants with a clinical diagnosis of AMD who completed the 22-item DLTV (DLTV-22) according to four-point ordinal response scale. An independent group of 386 participants with AMD were administered a reduced version of the DLTV with 11 items (DLTV-11), according to a five-point response scale. Rasch analysis was performed on both datasets and used to generate item statistics for measure order, response odds ratios per item and per person, and infit and outfit mean square statistics. The Rasch output from the DLTV-22 was examined to identify redundant items and for factorial validity and person item measure separation reliabilities. The average rating for the DLTV-22 changed monotonically with the magnitude of the latent person trait. The expected versus observed average measures were extremely close, with step calibrations evenly separated for the four-point ordinal scale. In the case of the DLTV-11, step calibrations were not as evenly separated, suggesting that the five-point scale should be reduced to either a four- or three-point scale. Five items in the DLTV-22 were removed, and all 17 remaining items had good infit and outfit mean squares. PCA with residuals from Rasch analysis identified two domains containing 7 and 10 items each. The domains had high person separation reliabilities (0.86 and 0.77 for domains 1 and 2, respectively) and item measure reliabilities (0.99 and 0.98 for domains 1 and 2, respectively). With the improved internal consistency, establishment of the accuracy and precision of the rating scale for the DLTV and the establishment of a valid domain structure we believe that it constitutes a useful instrument for assessing visual function in older adults with age-related macular degeneration.

Hierarchy of individual calibration levels for heart rate and accelerometry to measure physical activity

Combining accelerometry with heart rate (HR) monitoring may improve precision of physical activity measurement. Considerable variation exists in the relationships between physical activity intensity (PAI) and HR and accelerometry, which may be reduced by individual calibration. However, individual calibration limits feasibility of these techniques in population studies, and less burdensome, yet valid, methods of calibration are required. We aimed to evaluate the precision of different individual calibration procedures against a reference calibration procedure: a ramped treadmill walking-running test with continuous measurement of PAI by indirect calorimetry in 26 women and 25 men [mean (SD): 35 (9) yr, 1.69 (0.10) m, 70 (14) kg]. Acceleration (along the longitudinal axis of the trunk) and HR were measured simultaneously. Alternative calibration procedures included treadmill testing without calorimetry, submaximal step and walk tests with and without calorimetry, and nonexercise calibration using sleeping HR and gender. Reference accelerometry and HR models explained >95% of the between-individual variance in PAI (P < 0.001). This fraction dropped to 73 and 81%, respectively, for accelerometry and HR models calibrated with treadmill tests without calorimetry. Step-test calibration captured 62-64% (accelerometry) and 68% (HR) of the variance between individuals. Corresponding values were 63-76% and 59-61% for walk-test calibration. There was only little benefit of including calorimetry during step and walk calibration for HR models. Nonexercise calibration procedures explained 54% (accelerometry) and 30% (HR) of the between-individual variance. In conclusion, a substantial proportion of the between-individual variance in relationships between PAI, accelerometry, and HR is captured with simple calibration procedures, feasible for use in epidemiological studies.

Study of parameter stability of a lumped hydrologic model in a context of climatic variability

Central and West Africa were affected by an often marked reduction in rainfall and runoff around the year 1970. Has the behaviour of the catchments in these regions been changed as a result? Seventeen basins are used in this study, and are characterised by stationary or non-stationary annual rainfall or runoff time-series. An approach based on lumped hydrological modelling with a monthly time step (GR2M water balance model) and automatic parameter calibration is used to try to answer the question. Parameter stability of the models calibrated before and after the occurrence of possible rainfall or runoff deficit is analysed using estimations of confidence region. Minimisation of the least squares objective function provides a local optimum around which confidence regions are estimated in a non-linear context. The volumes of indifference represented by the confidence regions are analysed by their cross-sections on the planes defined by the three parameters of the model taken in pairs. For each basin, the cross-sections relative to different periods of calibration are interpreted in terms of possible parameter stability. This study shows that there is no link between parameter stability and the stationary behaviour of rainfall or runoff series of some catchments.

Rater Discrimination Using the Visual Analog Scale of the Physical Therapist Clinical Performance Instrument

Background and Purpose. A central issue surrounding the use of a visual analog scale (VAS) of the Physical Therapist Clinical Performance Instrument (CPI) is the level of measurement represented by the method. An often-made assumption is that the VAS is an interval-level measure of the construct of interest. In order for the scale to he valid and for this assumption to be supported, raters must demonstrate the ability to discriminate among 100 levels of student performance. The purpose of this study was to use a measurement model to investigate the validity of the VAS of the CPI when used by clinical instructors to evaluate student performance. Subjects. Final CPI raw scores were collected from 182 subjects from 3 different physical therapist education programs across 4 full-time clinical experiences. Methods. Visual analog scale raw scores for each item were measured (in millimeters) along with rater use of the With Distinction Box. An analysis using the Rasch Measurement Model was performed on the collected data. Step calibration values and average measure values provided by the model were used to analyze rater use of the VAS. Results. A valid rating scale was achieved when the VAS was considered to be a 6-level ordinal scale. Following the collapse of response categories, the 6 groupings of VAS raiu scores were as follows: 0-30 mm=l, 31-50 mm=2, 51-70 mm=3, 71-90 mm=4, 91-100 mm=5, and 100 mm + With Distinction Box=6. Discussion and Conclusion. The inability of clinical instructors to discriminate among 100 levels of student is most likely contributing to the invalid scale. Key Words: Clinical Performance Instrument, Rasch Measurement Model, Rater discrimination, Visual analog scale. INTRODUCTION The Physical Therapist Clinical Performance Instrument (CPI) was recently introduced for use in the assessment of physical therapist students during clinical fieldwork assignments.1 The CPI is a 24-item assessment tool that is believed to describe all essential aspects of professional practice of a physical therapist clinician performing at entry level. Individual competency items are rated by placing a mark on the given 100-mm visual analog scale (VAS), with novice clinical performance to entry-level performance anchoring the ends of the scale. A central issue surrounding the use of a VAS is the level of measurement represented by the method.2'6 An often-made assumption is that the VAS represents an interval-level measure of the construct of interest. Because an investigator applies a ruler to the 100-mm scale to extract a score, a conceptual leap to assuming interval-level measurement is often made/' If the construct of interest is length, the VAS represents a linear scale. However, when the VAS is utilized to assess another construct, such as clinical performance, the VAS is not necessarily assessing the construct at an interval level. Subsequently, research using the VAS of the CPI as an interval-level measure may lead to invalid inferences from the data. Psychometric investigation is required to support the use of the VAS as an interval-level measurement. The CPI has not been subjected to such a study. Related to the interval-level assumption of the VAS is the capacity for discrimination of the rater. If a pencil or pen mark is 1 mm wide, there are approximately 100 different levels of clinical the rater must distinguish among when using the VAS. The validity of the WS as an interval measure is based on the premise that a higher raw score represents a numerically defined increase in the construct of interest. Thus, an 80-mm mark on the WS for item 1 (safety) is assumed to represent twice as much ability related to safety as a 40-mm mark. The assumption is that the rater is able to distinguish among up to 100 distinct levels of response categories, or stimuli. The ability of individuals to distinguish among multiple levels of response categories, or stimuli, has been investigated in the psychological literature in the area of absolute judgment. …

Comparison of three accurate methods to measure AC voltage at low frequencies

Three methods for the determination of the RMS value of AC voltage at low frequencies are compared: the step calibration of a digitally synthesized source, the optimized sampling method, and the AC-DC voltage transfer with a multijunction thermal converter. The three methods agree within 1/spl times/10/sup -6/ with an uncertainty of 2.5/spl times/10/sup -8/ in the frequency range from 10 to 100 Hz.

Phase step calibration and phase measurement in image plane holography using &lt;inline-formula&gt;&lt;roman&gt;BaTiO&lt;/roman&gt;&lt;sub&gt;&lt;roman&gt;3&lt;/roman&gt;&lt;/sub&gt;&lt;/inline-formula&gt; crystal as a recording medium

A real-time visual approach for the calibration of phase step in image plane holography using BaTiO3 crystal as a recording medium is reported. In this method, the diffuse object is illuminated symmetrically with two collimated beams and a pump beam is added at the crystal plane. Each illuminating beam generates an individual interferogram at the observation plane when the object is subjected to load. A p phase shift to one of the illuminating beams results in the complete disappear- ance of the fringes due to phase reversal between the individual inter- ferograms, and at 2p phase change, the fringe pattern is restored. After calibration, a single-beam illumination configuration is used for phase measurement. We present the theory of the method and experimental results for a centrally loaded diaphragm rigidly clamped along the periph- ery. © 1998 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(98)01611-0)

A PORTABLE ANEMOMETER TO DETERMINE THE OUTPUT OF LARGE IN-PLACE VENTILATION FANS

The poultry industry could benefit from a rapid, efficient method to accurately determine the total volumetric flow rate of large, in-place ventilation fans. A portable anemometer using five, propeller-driven DC generators connected to a 386 PC provided volumetric flow rates accurate to within 1% when compared to approved laboratory procedures. A prototype was developed for 92-cm (36-in.) fans and the finished anemometer was designed for 122-cm (48-in.) fans. A computer integrated the DC voltages as the fixed five propeller array traversed the 130-cm (51-in.) square opening under control from the keyboard. The portable device was mounted on the suction side of an in-place fan and accurately monitored flows from 7 to 10 m3/s (15,000 to 21,000 cfm). An accurate traverse was completed in less than 4 min. Key steps in development and calibration of the system, detailed operational characteristics, and suggestions for its use are included.

A critical evaluation of resting intracellular free calcium regulation in dystrophic mdx muscle.

There are conflicting reports regarding whether resting free calcium levels ([Ca2+]i) are elevated in dystrophic mouse (mdx) myotubes and adult myofibers. We reinvestigated this question and found several lines of evidence supporting the hypothesis that increased calcium influx via leak channels leads to increases in resting [Ca2+]i. 1) Step calibration of fura 2/free acid in myofibers with use of microinjected Ca(2+)-ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid buffers revealed greater [Ca2+]i in dystrophic cells. Careful calibration of fura PE3-AM, a compartmentalization-resistant derivative of fura 2, also showed elevated [Ca2+]i in mdx myotubes. 2) Chronic, but not acute, application of tetrodotoxin reduced resting [Ca2+]i in dystrophic myotubes, suggesting that elevated resting [Ca2+]i is a consequence of previous long-term contractile activity. 3) Rates of manganese quenching of fura 2 fluorescence, an indirect indicator of calcium influx, were significantly higher in mdx myotubes and were increased by nifedipine, a calcium leak channel agonist. 4) Calcium leak channel activity, measured using patch clamping, was greater in the sarcolemma of adult non-enzyme-treated mdx myofibers.

IQQM—A hydrologic modelling tool for water resource and salinity management

A generic integrated water quantity and quality simulation model (IQQM) has been implemented in several regulated river systems in New South Wales, Australia, for water resources management planning. IQQM will eventually comprise four main components: an instream water quantity module, an instream water quality module, a rainfall-runoff/pollutant generation module and a groundwater quantity and quality module, although the pollutant generation and groundwater components are currently being developed. IQQM is designed to provide more reliable information relating to issues such as environmental flows and water quality than was possible with the monthly simulation models that have been used for water resource management planning studies in NSW for almost 20 years. One of the river systems for which IQQM is being implemented is the upper Hunter. One of the main roles for the Hunter IQQM will be to investigate options for managing salinity in the Hunter River. Implementation of IQQM Hunter has involved a multiple step calibration process. A description of the model is presented, and the multiple step process of calibration described. The results of model calibration are presented and the quality of calibration discussed.

Phase-measuring fiber optic electronic speckle pattern interferometer: phase step calibration and phase drift minimization

A phase-measuring fiber optic electronic speckle pattern interferometer (ESPI) was recently constructed and demonstrated. In this arrangement, phase stepping is introduced by stretching the fiber wrapped around a piezoelectric transducer. Calibration of the phase step is critical in phase measurement techniques for obtaining good phase plots. Methods used for calibrating the stretcher are outlined and the drifts in the phase caused by fluctuations in temperature and mechanical stresses are discussed. Ways to minimize this drift are also presented.