Consider the two linear regression models of Yij on Xij, namely Yij = βio + βij, Xij + Eij = 1, 2,…, ni, i = 1, 2, where Eij are assumed to be normally distributed with zero mean and common unknown variance σ2. The problem of estimating the conditional mean of Y1 for a given value of X1 is considered when it is a priori suspected that β10 = β20 and β11 = β21. The preliminary test estimator is proposed. The exact expressions for the bias and the mean square error of the estimator are derived. The relative efficiency of the new estimator to the usual least square estimator based on the first regression alone is computed and is used to determine the appropriate value of the significance level of the preliminary test β10 = β20 and β11 = β21. 相似文献
Consider the model Yijk=μ + ai + bij + eijk (i=1, 2,…, t; j=1,2,…, Bi; k=1,2…,nij), where μ is a constant and a1,bij and eijk are distributed independently and normally with zero means and variances σ2adij and σ2, respectively, where it is assumed that the di's and dij's are known. In this paper procedures for estimating the variance components (σ2, σ2a and σ2b) and for testing the hypothesis σ2b = 0 and σ2a = 0 are presented. In the last section the mixed model yijk, where xijkkm are known constants and βm's are unknown fixed effects (m = 1, 2,…,p), is transformed to a fixed effect model with equal variances so that least squares theory can be used to draw inferences about the βm's. 相似文献
A new testing procedure is derived which enables to assess the equivalence of two arbitrary noncontinuous distribution functions from which unrelated samples are taken as the data to be analyzed. The equivalence region is defined to consist of all pairs (F,G) of distribution functions such that for independent X ∼ F, Y ∼ G the conditional probability of {X > Y} given {X ≠ Y} lies in some short interval around 1/2. The test rejects the null hypothesis of nonequivalence if and only if the standardized distance between the U-statistics estimator of P[X > Y ∣ X ≠ Y] and the center of the equivalence interval (1/2 — ε1, 1/2 + ε2) does not exceed a critical upper bound which has to be computed as the α-quantile of a χ2-distribution with one degree of freedom and a random noncentrality parameter proportional to the squared length of that interval. The test is shown to maintain the asymptotic significance level under very weak regularity conditions. Results of an extensive simulation study suggest that its level properties are very satisfactory in small samples as well. The power turns out to be inversely related to the rate P[X = Y] of ties between observations from different samples. 相似文献
By a suitable transformation of the pairs of observations obtained in the successive periods of the trial, bioequivalence assessment in a standard comparative bioavailability study reduces to testing for equivalence of two continuous distributions from which unrelated samples are available. Let the two distribution functions be given by F(x) = P[X ≤ x], G(y) = P[Y ≤ y] with (X, Y) denoting an independent pair of real-valued random variables. An intuitively appealing way of putting the notion of equivalence of F and G into nonparametric terms can be based on the distance of the functional P[X > Y] from the value it takes if F and G coincide. This leads to the problem of testing the null hypothesis Ho P[X > Y] ≤ 1/2 - ε1 or P[X > Y] ≥ 1/2 + ε2 versus H1 : 1/2 ? ε1 < P[X > Y] < 1/2 + ∈2, with sufficiently small ε1, ε2 ∈ (0, 1/2). The testing procedure we derive for (0, H1) and propose to term Mann-Whitney test for equivalence, consists of carrying out in terms of the U-statistics estimator of P[X > Y] the uniformly most powerful level a test for an interval hypothesis about the mean of a Gaussian distribution with fixed variance. The test is shown to be asymptotically distribution-free with respect to the significance level. In addition, results of an extensive simulation study are presented which suggest that the new test controls the level even with sample sizes as small as 10. For normally distributed data, the loss in power as against the optimal parametric procedure is found to be almost as small as in comparisons between the Mann-Whitney and the t-statistic in the conventional one or two-sided setting, provided the power of the parametric test does not fall short of 80%. 相似文献
For estimating the finite population mean Y- of the study character y, an estimator using a transformed auxiliary variable has been defined. The bias and mean-squared error (MSE) of the proposed estimator have been obtained. The regions of preference have been obtained under which it is better than usual unbiased estimator y-, the ratio estimator y-R = y-X-/x-, Sisodia and Dwivedi (1981) estimator y-s = y-(X- + Cx)/(x- + Cx) and Singh and Kakran (1993) estimator y-k = y[X- + β2(x)]/[x- + β2(x)]. An empirical study has been carried out to demonstrate the superiority of the suggested estimator over the others. 相似文献
This study investigated the utility of a 23 factorial design and optimization process for polylactic-co-glycolic acid (PLGA) nanoparticles containing itraconazole with
5 replicates at the center of the design. Nanoparticles were prepared by solvent displacement technique with PLGAX1 (10, 100 mg/mL), benzyl benzoateX2 (5, 20 μg/mL), and itraconazoleX3 (200, 1800 μg/mL). Particle size (Y1), the amount of itraconazole entrapped in the nanoparticles (Y2), and encapsulation efficiency (Y3) were used as responses. A validated statistical model having significant coefficient figures (P<.001) for the particle size (Y1), the amount of itraconazole entrapped in the nanoparticles (Y2), and encapsulation efficiency (Y3) as function of the PLGA (X1), benzyl benzoate (X2), and itraconazole (X3) were developed: Y1=373.75+66.54X1+52.09X2+105.06X3−4.73X1X2+46.30X1X3; Y2=472.93+73.45X1+ 169.06X2+333.03X3+62.40X1X3+141.49X2X3; Y3= 57.36+6.53X1+15.52X2−12.59X3+1.01X1X3+ 1.73X2X3.X1,X2, andX3 had a significant effect (P<.001) onY1,Y2, andY3. The particle size, the amount of itraconazole entrapped in the nanoparticles, and the encapsulation efficiency of the 4
formulas were in agreement with the predictions obtained from the models (P<.05). An overlay plot for the 3 responses shows the boundary in whichY1 shows the boundary in which a number of combinations of concentration of PLGA, benzyl benzoate, and itraconazole will result
in a satisfactory process. Using the desirability approach with the same constraints, the solution composition having the
highest overall desirability (D=0.769) was 10 mg/mL of PLGA, 16.94 μg/mL of benzyl benzoate, and 1001.01 μg/mL of itraconazole.
This approach allowed the selection of the optimum formulation ingredients for PLGA nanoparticles containing itraconazole
of 500 μg/mL. 相似文献
The aim of this study was to systematically obtain a model of factors that would yield an optimized self-nanoemulsified capsule
dosage form (SNCDF) of a highly lipophilic model compound, Coenzyme Q10 (CoQ). Independent variables such as amount of R-(+)-limonene
(X1), surfactant (X2), and cosurfactant (X3), were optimized using a 3-factor, 3-level Box-Behnken statistical design. The dependent variables selected were cumulative
percentage of drug released after 5 minutes (Y1) with constraints on drug release in 15 minutes (Y2), turbidity (Y3), particle size (Y4), and zeta potential (Y5). A mathematical relationship obtained,Y1=78.503+6.058X1 +13.738X2+5.986X3−25.831X12
+9.12X1X2−26.03X1X3−38.67X22
+11.02X2X3−15.55X33
(r2=0.97), explained the main and quadratic effects, and the interaction of factors that affected the drug release. Response
surface methodology (RSM) predicted the levels of factorsX1,X2, andX3 (0.0344, 0.216, and 0.240, respectively), for a maximized response ofY1 with constraints of >90% release onY2. The observed and predicted values ofY1 were in close agreement. In conclusion, the Box-Behnken experimental design allowed us to obtain SNCDF with rapid (>90%)
drug release within 5 minutes with desirable properties of low turbidity and particle size. 相似文献
Adenosine 5′-triphosphate (ATP) is an extracellular signal that regulates various cellular functions. Cellular secretory activities
are enhanced by ATP as well as by cholinergic and adrenergic stimuli. The present study aimed to determine which purinoceptors
play a role in ATP-induced changes in the intracellular concentration of calcium ions ([Ca2+]i) and in the fine structure of acinar cells of rat lacrimal glands. ATP induced exocytotic structures, vacuolation and an
increase in [Ca2+]i in acinar cells. The removal of extracellular Ca2+ or the use of Ca2+ channel blockers partially inhibited the ATP-induced [Ca2+]i increase. U73122 (an antagonist of PLC) and heparin (an antagonist of IP3 receptors) did not completely inhibit the ATP-induced [Ca2+]i increase. P1 purinoceptor agonists did not induce any changes in [Ca2+]i, whereas suramin (an antagonist of P2 receptors) completely inhibited ATP-induced changes in [Ca2+]i. A P2Y receptor agonist, 2-MeSATP, induced a strong increase in [Ca2+]i, although UTP (a P2Y2,4,6 receptor agonist) had no effect, and reactive blue 2 (a P2Y receptor antagonist) resulted in partial inhibition. The potency
order of ATP analogs (2-MeSATP > ATP ⋙ UTP) suggested that P2Y1 played a significant role in the cellular response to ATP. BzATP (a P2X7 receptor agonist) induced a small increase in [Ca2+]i, but α,β-meATP (a P2X1,3 receptor agonist) had no effect. RT-PCR indicated that P2X2,3,4,5,6,7 and P2Y1,2,4,12,14 are expressed in acinar cells. In conclusion, the response of acinar cells to ATP is mediated by P2Y (especially P2Y1) as well as by P2X purinoceptors. 相似文献
Consider the model yijk=u ± ai ± bi ± cij ± eijk i=1, 2,…, t; j=1, 2,…b; k=1, 2,…,nij where μ is a constant and ai, bi, cij are distributed independently and normally with zero means and variances Δ2 Δ2/bdij and δ2 respectively. It is assumed that di's, and dij's are known (positive) constants (for all i and j). In this paper procedures for estimating the variance components (Δ2, Δ2b and Δ2a) and for testing the hypothesis Hoc:Δ2c/Δ2 = y3 and Hoa:Δ2b/Δ2 = y4 (where y2, y3, and y4, are specified constants) are presented. A generalization for the mixed model case is discussed in the last section. 相似文献
The model used in this paper is Y = Xβ, where with unknown x0. Estimators of x0 are derived by putting βmx0 =βm+1 regarding βm+1 as a new unknown parameter. Formally we use the model Y = X1β+ + e where β′+ = (β0, …βm+1 and Then βm+1/ βm is a point estimator of x0. Assuming normality for e and taking the random variable z=βmx0?βm+1 we get a t-distributed variable and finally a confidence estimator of x0. The formulas are applied in dose response relations in antibiotic assays refering to a standard. Now we can take into account not only the dependence on the dose/concentration but also on the position on the test agar plate where the test solution is filled in. As a consequence the confidence interval of the unknown dose/concentration x0 becomes shorter and by it the statements more precise. 相似文献
A perennial problem in statistics is the determination of biases, variances and covariances for functions of random variables X1, X2, …, Xn which themselves have a known distribution. A common approach is through equations based upon Taylor series approximations but a “point evaluation” method may sometimes be a useful alternative. This involves approximating the multivariate distribution of the X variables by the 2n points given by X1=μ1±1, X2 = μ2 ±2, …, Xn = = μn μn, where μi is the mean and σi the standard deviation of Xi, with appropriate point weights. An advantage over the Taylor series approach is that function derivatives do not have to be explicitely calculated. The point evaluation method is particularly useful in cases where the X variables are uncorrelated. Then the evaluation of the 2n points can be replaced by the evaluation of 2n points. The point evaluation method is illustrated with powers of a normally distributed variable, and with estimation of gene frequencies from ABO blood group frequencies. 相似文献
Abstract The solution distribution of combinations of the sugar ring puckering domains, C2′endo(S), C3′endo(N), and C4′-C5′ rotamers, +sc(g+), ap(t), -sc(g?), in α and β-anomers in ribo- and deoxyribo- pyrimidine nucleic acid components can be determined from vicinal coupling constants (M. Remin, J. Biomol. Str. Dyn. 2, 211 (1984). A general correlation pattern with a conformational constant λ, reflecting an intrinsic physical property of the sugar - side chain ensemble, is developed and expressed in terms of four principles: I) The +sc rotamer contributes to the C3′endo population to a higher extent (1 - Yt) than to C2′endo,(l-Yt-Yg-/Xs). II) The ap rotamer contributes to both C2′endo and C3′endo populations to the same extent (Yt). III) The—sc rotamer contributes only to the C2′endo population, (Yg-/Xs). IV) The molar fractions Xs, Yt and Yg- of conformations C2′endo, ap and—sc, respectively, are strongly correlated, λ = (Yg-/Xs)/Yt ≈ 0.5, and therefore Yt is a basic variable parameter which determines all others in the correlation pattern. In α-anomers, regardless of the type and conformation of the sugar ring and base, the molar fraction Yt = 0.37 ± 0.02. This finding means that different α-anomers show one correlation pattern free of the influence of the base. In β-anomers, structure and conformation of the base are important factors which modulate (through Yt) the correlation pattern, conserving its fundamental features. Yt is considerably increased by a syn-oriented pyrimidine base, but decreases when the base is anti. The transition from anti to syn orientation of the base is followed by destabilization of (C2′endo, +sc) in favor of (C3′endo, ap). The principles of conformational correlations rationalize a variety of correlations observed in the past. 相似文献
Methodological issues in the analysis of incidence rates or prevalence proportions for count data, presented in a form of a sequence of 2×2 tables, corresponding to levels (strata) of a specified variable (risk factor) X, are discussed. Suppose λ1i and λ2i are the incidence rates of an event D in the ith stratum for populations 1 and 2, respectively. The homogeneity (null) hypothesis is formulated in the form: H0:λ1i=λ2i for all i (i = 1, 2, …, I). Three X2-tests for H0 and their theoretical bases are discussed: XTotal2 which is sensitive to alternatives HA :λ1i± λ2i for at least some i; XComb2 which is sensitive to alternatives HA : λ1iλ2i2or < λ2i but not both for all i; and XDiff2 which is sensitive to alternatives HA:λ1i>λ2i3 for some i and λ1i′ < λ2i′ for some i′ (i≠i′). These statistics satisfy the relation XTotal2 = XComb2 + XDiff2. Also, X′2-statistic for pooled data is calculated, which in conjunction with XComb2 can serve for detecting confounding. Although most of these techniques are known, they are rather scattered in the literature, and not always considered jointly, as it is emphasized in the present paper. It is hoped that these comments will be helpful to biostatisticians as well as to epidemiologists and medical researchers in the analysis of mortality and morbidity data. For illustration, two examples with large sets of epidemiological data are given. 相似文献
The multivariate general Gauss-Markoff (MGM) model (U, XB, ∑?σ2V) when the matrices V ≥ 0 and ∑ > 0 are known and the scalar σ2 > 0 is unknown, is considered. The present paper is a continuation of two earlier works (Oktaba, 1988a, b). If XB = X1Σ + X2Δ, then the F-test for verification the hypothesis WΣA = 0 is presented. Moreover, under conditions of orthogonality the decomposition of the matrix SA (?BCA)′L?(?BCA) into the sum of s = r(L) matrices is given, where ?BCA is the estimator of the parametric estimable functions ?BCA, Cov (?BCA) = A′ ∑?σ2L = ?C4?′, B? = (X′T?X)?X′T?U, C4 = (X′T?X)?M, where M = M′ is any arbitrary matrix such that R(X) ? R(T), T=V+XMX′; T? is any c-inverse. R(A) is the linear space generated by the colums of A. Then under additional assumption on normality of U the statistics F for testing ?BA = 0 is deduced. Under conditions of normality of U and decomposition of SA, the statistics F1, …, Fs for the hypotheses jiBA = 0 (i = 1,…, s) are established. 相似文献
Extracellular nicotinamide adenine dinucleotide (NAD+) is known to increase the intracellular calcium concentration [Ca2+]i in different cell types and by various mechanisms. Here we show that NAD+ triggers a transient rise in [Ca2+]i in human monocytes activated with lipopolysaccharide (LPS), which is caused by a release of Ca2+ from IP3-responsive intracellular stores and an influx of extracellular Ca2+. By the use of P2 receptor-selective agonists and antagonists we demonstrate that P2 receptors play a role in the NAD+-induced calcium response in activated monocytes. Of the two subclasses of P2 receptors (P2X and P2Y) the P2Y receptors were considered the most likely candidates, since they share calcium signaling properties with NAD+. The identification of P2Y1 and P2Y11 as receptor subtypes responsible for the NAD+-triggered increase in [Ca2+]i was supported by several lines of evidence. First, specific P2Y1 and P2Y11 receptor antagonists inhibited the NAD+-induced increase in [Ca2+]i. Second, NAD+ was shown to potently induce calcium signals in cells transfected with either subtype, whereas untransfected cells were unresponsive. Third, NAD+ caused an increase in [cAMP]i, prevented by the P2Y11 receptor-specific antagonist NF157. 相似文献
This paper is motivated by a practical problem relating to student performance in a number of subjects of equal standing. Its mathematical formulation is to find an approximation to a multivariate probability of the form Pr {X1⩾a, X2⩾a, …, XN⩾a} for arbitrary a and N, in terms of p = Pr {X1⩾a} and q = Corr (Xi, Xj), i≠j, where Xi, i = 1, …, N are exchangeable random variables with mean 0 and variance unity. 相似文献
The statistical properties of one estimator of absolute genetic distance (1/2) K∑i=1 |pxi-yr|, tween two populations X and Y, are presented. It is shown that using this distance in small samples can be misleading particularly when populations are close to each other. 相似文献
A class of almost unbiased ratio estimators for population mean σ is derived by weighting sample σ = (1/n) σ yi, ratio estimators σ and an estimator, σ (yi/xi). It is shown that NIETO DE PASCUAL (1961) estimator is a particular member of the class and an optimum estimator in the class (in the minimum variance sense) is identified. The results are illustrated through two numerical examples. 相似文献
Given independent multivariate random samples {Xij: j = 1, …, ni} from Fi, for i = 1,2, a test is desired for H0: F1 = F2 against general alternatives. Consider the k · (n1 + n2) possible ways of choosing one observation from the combined samples and then one of its k nearest neighbors, and let Sk be the proportion of these choices in which the point and neighbor are in the same sample. Schilling (1986) proposed Sk as a test statistic, but did not indicate how to determine k. We suggest as test statistic W = N Σ kSk, which we show is equivalent to a sum of N Wilcoxon rank sums, and also to a sum of two two-sample U-statistics of degrees (1, 2) and (2, 1). Simulation with multivariate normal data suggests that our test is generally more powerful than Schilling's test using k = 1, 2, or 3. We illustrate its use with Fisher's iris data. 相似文献