Search results for "Observational error"
showing 10 items of 40 documents
Characterization of impervious layers using scale models and an inverse method
2009
We describe a novel procedure that uses an inverse method to determine unknown parameters for impervious layers used in multilayer structures. The proposed model of the multilayer structure is limited to an ideal double plate separated by an unbonded, fibrous, sound-absorbing material. Experimental data were obtained by nearfield acoustic holography for the calculation of the transmission loss of various multilayer structures mounted in a window in a wooden box designed specifically for this purpose. We used the Trochidis and Kalaroutis forecast model of acoustic insulation for multilayer structures, which is based on a spatial Fourier transform. The experimental pressure and velocity data …
Vectofocimetry: Dioptric power measurement in manual focimeters using power vectors
2021
Abstract Dioptric power measurement is classically achieved using manual focimeters. In this contribution, we present vectofocimetry as a novel methodology to be easily implemented in manual focimeters for improving their capabilities regarding dioptric power measurement. The new procedure is conceptually based on power vector formalism of dioptric power which represents the dioptric power as three values in the form of [M, J0, J45], it uses an iterative process of blur reduction, and it only requires a few modifications in the device that are easy-to-adapt and cost-effective. As a result, dioptric power measurements are easily and quickly obtained with comparable results to the reported on…
Returns to Schooling in Spain: How Reliable are Instrumental Variable Estimates?
2002
This paper studies the ordinary least–squares (OLS) and instrumental variable (IV) estimates of the returns to schooling for male workers in Spain. OLS estimates are often biased due to the endogeneity of schooling, measurement errors or omitted variables. Proper IV estimates correct this bias. The reliability of family background, natural experiments (based on changes in the education system and season of birth) and the availability of a college in the province is checked using Spanish data. The results suggest that background and college availability are valid instruments and that the IV estimates of the returns to schooling are higher than OLS estimates. These results are in line with th…
Strain Measurement on Composites: Errors due to Rosette Misalignment
2002
Electrical resistance strain gauges are increasingly used for the determination of the strain field in composite components. The effect of the angular misalignment of a strain gauge rosette on the determination of the strains in a composite material is investigated in this paper. The theoretical analysis shows that the strain error along the principal material directions depends on the difference of principal strains, on the angular misalignment of the rosette and on the angle between the maximum principal strain and the fibre direction. The paper also shows experimental evidence for the theoretical analysis.
HUMAN CAPITAL IN GROWTH REGRESSIONS: HOW MUCH DIFFERENCE DOES DATA QUALITY MAKE?.
2000
We construct a revised version of the Barro and Lee (1996) data set for a sample of OECD countries using previously unexploited sources and following a heuristic approach to obtain plausible time profiles for attainment levels by removing sharp breaks in the data that seem to reflect changes in classification criteria. It is then shown that these revised data perform much better than the Barro and Lee (1996) or Nehru et al (1995) series in a number of growth specifications. We interpret these results as an indication that poor data quality may be behind counterintuitive findings in the recent literature on the (lack of) relationship between educational investment and growth. Using our prefe…
Analysis of the spawning stock-recruitment relationship of vendace (Coregonus albula (L.)) with evaluation of alternative models, additional variable…
2004
– Spawning biomass and recruitment data for vendace from a central Finnish lake were analysed by fitting various recruitment models and comparing the fits statistically. The compensatory models of Ricker, Cushing and Beverton & Holt fitted the data better than the H0 hypothesis of constant proportionality, but model and parameter uncertainties were high. Additional variables were included in an attempt to reduce uncertainties. Heavy wind forcing during the first month after hatching of larvae reduced the recruitment success. For the Ricker and the Cushing models, recruitment seemed to be also negatively associated with the density of the previous year-class. The r2 increased considerably w…
Error calculation for the PSA quotient.
2008
Abstract Objective Prostate specific antigen (PSA) assays have significant measurement errors, but the error associated with the PSA quotient (free to total PSA) often remains unknown. Methods We used both Gaussian error calculation and measurement of imprecision to investigate the level of error associated with the PSA quotient. Results Surprisingly, we found that the error of the PSA quotient at low levels is markedly smaller than that of the total PSA value. Conclusions The PSA quotient should be calculated and considered as a clinically relevant value.
Selection Correction in Panel Data Models: An Application to Labour Supply and Wages
2000
In recent years a number of panel estimators have been suggested for sample selection models, where both the selection equation and the equation of interest contain individual effects which are correlated with the explanatory variables. We review and compare some of these estimators, and apply them to estimating the return to actual labour market experience for females, using a panel of twelve years. All these estimators rely on the assumption of strict exogeneity of regressors in the equation of interest, conditional on individual specific effects and the selection mechanism. This assumption is likely to be violated in many applications. Also, life history variables are often measured with…
SM identification of approximating models forH∞ robust control
1999
Set Membership (SM) W, identification of mixed parametric and nonparametric models is investigated, aimed to estimate a low order approximating model and an identification error, giving a measure of the unmodeled dynamics in a form well suited for H, control methodologies. In particular, the problem of estimating the parameters of the parametric part and the H, bound on the modeling error is solved using frequency domain data, supposing lbo bounded measurement errors and exponentially stable unmodeled dynamics. The effectiveness of the proposed procedure is tested on some numerical examples, showing the advantages of the proposed methods over the existing nonparametric H, identification app…
Estimation of errors in mechanical efficiency
1990
Errors in measurements of mechanical work, net energy expenditure and mechanical efficiency (ME) were calculated, when subjects performed isolated eccentric or concentric muscle actions and combinations of these actions [stretch-shortening cycle (SSC) exercises] with a special sledge apparatus. The relative error of mechanical work was 6.1%. When estimating the error of energy metabolism from oxygen consumption the error would be about 4% (McArdle et al. 1981). The maximum error of ME was the sum of these two values (10.1%). Obviously the error of ME was less than 5%, because 30 muscle actions were averaged and, in addition, the errors of mechanical work and energy expenditure were not in t…