منابع مشابه
Standard error correction in two-stage estimation with nested samples
Data at different levels of aggregation are often used in two-stage estimation, with estimates obtained at the higher level of aggregation entering the estimation at the lower level of aggregation. An example is customers within markets: first-stage estimates on market data provide variables that enter the second-stage model on customers. We derive the asymptotic covariance matrix of the second...
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In this paper we discuss the properties of confidence intervals for regression parameters based on robust standard errors. We discuss the motivation for a modification suggested by Bell and McCaffrey (2002) to improve the finite sample properties of the confidence intervals based on the conventional robust standard errors. We show that the Bell-McCaffrey modification is a natural extension of a...
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Prediction using pure standards is expected to be biased whenever the slope of the calibration is affected by the presence of sample matrix. Moreover, in the presence of unknown spectral interferents, first-order algorithms like partial least squares cannot be used. In this study, a method for determination of carvedilol (CAR) in tablet and urine samples is proposed by excitation-emission fluor...
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A simple technique for the collection and equilibration of capillary samples of blood is described for the measurement of pH, PCO(2), and standard bicarbonate by the interpolation method. The possible errors of collecting blood in open-ended capillary tubes containing wet heparin are examined. The method has proved to be accurate, providing the technique is strictly adhered to, and has proved e...
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Chlorophyll analysis at high precision and accuracy is limited by the lack of suitable, commercially available internal standards for HPLC analysis. Here, the commercially available dye zinc-phthalocyanine is presented as a new internal standard to quantify chlorophylls in vegetable foods and to detect chlorophyll degradation products. The technique was applied to chlorophyll analysis of a sele...
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ژورنال
عنوان ژورنال: Science
سال: 1953
ISSN: 0036-8075,1095-9203
DOI: 10.1126/science.117.3027.3-s