摘要:

AbstractTwo new methods for computing confidence intervals for the difference δ = p1— p2between two binomial proportions (p1, p2) are proposed. Both the Mid‐P and Max‐P likelihood weighted intervals are constructed by mapping the tail probabilities from the two‐dimensional (p1, p2)‐space into a one‐dimensional function of δ based on the likelihood weights. This procedure may be regarded as a natural extension of the CLOPPER‐PEARSON (1934) interval to the two‐sample case where the weighted tail probability is α/2 at each end on the δ scale. The probability computation is based on the exact distribution rather than a large sample approximation. Extensive computation was carried out to evaluate the coverage probability and expected width of the likelihood‐weighted intervals, and of several other methods. The likelihood‐weighted intervals compare very favorably with the standard asymptotic interval and with intervals proposed by HAUCK and ANDERSON (1986), COX and SNELL (1989), SANTNER and SNELL (1980), SANTNER and YAMAGAMI (1993), and PESKUN (1993). In particular, the Mid‐P likelihood‐weighted interval provides a good balance between accurate coverage probability and short interval width in both small and large samples. The Mid‐P interval is also comparable to COE and TAMHANE'S (1993) interval, which has the best

ISSN:0323-3847    

DOI:10.1002/bimj.4710390402

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractTo study the effect of methadone treatment in reducing multiple drug use, say heroin and benzodiazepines while controlling for their possible interaction, we analyse the results of urine drug screens from patients in treatment at a Sydney clinic in 1986. Weekly tests are either positive or negative for each type of drug and a bivariate binary model was developed to analyse such repeated bivariate binary outcomes. It models simultaneously the logit of each type of drug use and their log odds ratio linearly in some covariates. The serial correlation within subject is accounted for by including the ‘previous outcome’ of both drugs and their interaction as covariates. Our main conclusion is that drug use is reduced over time and the interaction between dose and time effects is not significant. It also suggests that while methadone maintenance is effective in reducing heroin use (CHAN et al., 1995), it does not suppress non‐opioid drug use. Concerning the association between the two drugs, it is found that the present strength of their association depends on the previous outcomes only through a measure of concordance. The proposed model has a tractable likelihood function and so a full likelihood analysis is possible. It can be easily extended to incorporate mixture effects. The EM algorithm is used for the estimation of parameters in the mixture model and model selection can be based on the Akaike Information Crit

ISSN:0323-3847    

DOI:10.1002/bimj.4710390403

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractAn improved version of the test of CROCKETT (1979) for testing for the bivariate Poisson distribution is given and evaluated.

ISSN:0323-3847    

DOI:10.1002/bimj.4710390404

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractIt is shown that any discrete distribution with non‐negative support has a representation in terms of an extended Poisson process (or pure birth process). A particular extension of the simple Poisson process is proposed: one that admits a variety of distributions; the equations for such processes may be readily solved numerically. An analytical approximation for the solution is given, leading to approximate mean‐variance relationships. The resulting distributions are then applied to analyses of some biological data

ISSN:0323-3847    

DOI:10.1002/bimj.4710390405

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractInvestigations of sample size for planning case‐control studies have usually been limited to detecting a single factor. In this paper, we investigate sample size for multiple risk factors in strata‐matched case‐control studies. We construct an omnibus statistic for testingMdifferent risk factors based on the jointly sufficient statistics of parameters associated with the risk factors. The statistic is non‐iterative, and it reduces to the Cochran statistic whenM= 1. The asymptotic power function of the test is a non‐central chi‐square withMdegrees of freedom and the sample size required for a specific power can be obtained by the inverse relationship. We find that the equal sample allocation is optimum. A Monte Carlo experiment demonstrates that an approximate formula for calculating sample size is satisfactory in typical epidemiologic studies. An approximate sample size obtained using Bonferroni's method for multiple comparisons is much larger than that obtained using the omnibus test. Approximate sample size formulas investigated in this paper using the omnibus test, as well as the individual tests, can be useful in designing case‐control studies for detecting multiple

ISSN:0323-3847    

DOI:10.1002/bimj.4710390406

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractA Monte Carlo simulation was conducted in order to determine the size and power of two proposed tests (the covariance and correlation tests) for three‐factor interaction in 2 × 2 × 2 contingency tables. Results were compared to the log‐odds ratio test statistic. Simulation showed the correlation test to be more conservative than the covariance test, but less so than the log‐odds ratio test. However, the correlation test was the most powerful among the thre

ISSN:0323-3847    

DOI:10.1002/bimj.4710390407

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractThe power of single contrast tests strongly depends on the a priori unknown shape of the dose response relationship. Two approaches can be used to overcome this major disadvantage: the likelihood ratio test for order restriction or multiple contrast tests. Within the closure principle, the shape for the different hyptheses varies. Therefore multiple contrast tests are used as trend tests. Based on a simulation study the power advantage of this approach in comparison with single contrast tests is demonstrated.

ISSN:0323-3847    

DOI:10.1002/bimj.4710390408

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractFor the c‐sample location problem with umbrella alternatives we present a modification of a test proposed by BARLOW et al. (1972) for trend alternatives. Furthermore, we study a rank version of this modified test following a proposal of CONOVER and IMAN (1981). These tests are compared with the test of MACK and WOLFE (1978) and with some so called Mack‐Wolfe‐type tests in which the Mann‐Whitney statistics are replaced by other two‐sample linear rank statistics. The comparison is referred to the power of the test assuming a broad range of distributions. It will be shown firstly, that for nonnormal data there are tests with higher power than the modification of the test of Barlow et al. and secondly, that for a special distribution there is a Mack‐Wolfe‐type test which is more efficient than is competitors. We also consider the case of

ISSN:0323-3847    

DOI:10.1002/bimj.4710390409

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

摘要:

AbstractAn important indicator for the long‐term recovery after valve replacement surgery is postoperative valve gradient. This information is available only for patients received catheterization or echocardiogram postoperatively. It is plausible that sicker patients are more inclined to undergo these postoperative procedures and their valve gradients tend to be higher. Under this situation, ignoring the missing values and using sample mean based on the available information as an estimate of the whole study population leads to overestimation. Regression estimator is a reasonable choice to eliminate this bias if independent (explanatory) variables closely associated with both residual valve gradient and non‐response mechanism can be identified. Using a series of patients receiving St. Jude Medical prosthetic valves, we found that valve area index can be used as an independent variable in the regression estimator. Two digressions from the standard assumptions used in linear regression, heteroscedastic trend of the error term and outliers were found in the data set. Iteratively reweighted least square (IRLS) was adopted to handle heteroscedasticity. Influence function approach was used to evaluate the sensitivity of outliers in regression estimator. Under an equal response rate mechanism, IRLS not only solves the problem of heteroscedasticity, but is also less sensitive to outli

ISSN:0323-3847    

DOI:10.1002/bimj.4710390410

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY

ISSN:0323-3847    

DOI:10.1002/bimj.4710390411

出版商:WILEY‐VCH Verlag    

年代:1997

数据来源: WILEY