Confounding of algorithmic efficiency by programming language in exact odds ratio estimation.
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Algorithms↗
Biomedical subjects
K F Hirji
Publications and source records attributed to K F Hirji.
Clinical characteristics of tuberculous lymphadenitis in Tanzania.
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Biopsy↗
Nosocomial bacterial infections among children with severe protein energy malnutrition.
The incidence of hospital acquired acute bacterial infections among 164 severely malnourished children admitted to the paediatric wards at the Muhimbili Medical Centre in Dar es Salaam were studied. On admission, ninety two per cent of the patients had at least one form of bacterial infection. During the subsequent two weeks hospital stay, 49% of the patients acquired a new infection. Septicaemia and urinary tract infection (UTI) were the commonest infections. Staphylococcus aureus was the commonest organism in the former, while gram negative organisms, Escherichia coli and Klebsiella species, were predominant in the latter. Pathogens similar to those found from patients were cultured from random samples taken from the floor, beds, towels, sinks and antiseptic containers in the wards. Sensitivity patterns of isolated pathogens to antimicrobial agents showed that S. aureus was highly sensitive to cloxacillin, erythromycin, and gentamicin, while the gram negative organisms were highly sensitive to gentamicin. Our study shows that the problem of nosocomial infection in paediatric wards requires urgent attention. There is a need to institute preventive measures including provision of proper nursing care, maintenance of sterile environment, and reduction of duration of hospital stay.
Academic Medical Centers↗
Carcinoma of the male breast in Tanzania.
This is a retrospective study of male mammary carcinoma in Tanzania based on biopsy material received from 1974 to 1987 at the Tanzania Cancer Registry. In a series of 1104 cases of breast cancer, 76 or 6.5% were male. This compares with approximately 1% in Western literature, and a similar or higher percentage in some other African countries. In Africa, medical facilities are limited, and appropriate surgical treatment, radiotherapy, and chemotherapy are difficult to procure. By the time cases reach the main hospitals, the cancer is often in a very advanced stage. Thus, there is a need to ensure early referral of cases. Further, for disseminated carcinoma, the more frequent use of orchidectomy should be considered. Orchidectomy is a simple and potentially effective procedure that can be undertaken at any hospital.
Adolescent↗
A quasi-exact test for comparing two binomial proportions.
The use of the Fisher exact test for comparing two independent binomial proportions has spawned an extensive controversy in the statistical literature. Many critics have faulted this test for being highly conservative. Partly in response to such criticism, some statisticians have suggested the use of a modified, non-randomized version of this test, namely the mid-P-value test. This paper examines the actual type I error rates of this test. For both one-sided and two-sided tests, and for a wide range of sample sizes, we show that the actual levels of significance of the mid-P-test tend to be closer to the nominal level as compared with various classical tests. The computational effort required for the mid-P-test is no more than that needed for the Fisher exact test. Further, the basis for its modification is a natural adjustment for discreteness; thus the test easily generalizes to r x c contingency tables and other discrete data problems.
Binomial Distribution↗
A microcomputer program for exact and asymptotic analysis of several 2 x 2 tables.
A microcomputer program for analysis of a binomial proportion and the common odds ratio in a series of 2 x 2 tables is presented. This program utilizes both exact and asymptotic methods to provide point estimates, P values, and confidence intervals. Modifications of the exact method based on the concept of a mid-P value are also included. The program allows the user to compare the exact coverage properties of various methods of computing confidence intervals. Use of an improved algorithm provides considerable gains in computational efficiency.
Algorithms↗
Evaluation of exact and asymptotic interval estimators in logistic analysis of matched case-control studies.
We compare six methods for constructing confidence intervals for a single parameter in stratified logistic regression. Three of these are based on inversion of standard asymptotic tests--namely, the Wald, the score, and the likelihood ratio tests. The other three are based on the exact distribution of the sufficient statistic for the parameter of interest. These include the traditional exact method of constructing confidence intervals, and two others, the mid-P and mean-P methods, which are modifications of this procedure that aim at reducing the conservative bias of the exact method. Using efficient algorithms, the six methods are compared by determination of their exact coverage levels in a series of conditional sample spaces. An incident case-control study of lung cancer in women is used to further illustrate the differences among the various methods. Computation of coverage functions is seen as a useful graphical diagnostic tool for assessing the appropriateness of different methods. The mid-P and the score methods are seen to have better coverage properties than the other four.
Biometry↗
A comparison of exact, mid-P, and score tests for matched case-control studies.
A recently developed algorithm for generating the distribution of sufficient statistics for conditional logistic models can be put to a twofold use. First, it provides an avenue for performing inference for matched case-control studies that does not rely on the assumption of a large sample size. Second, joint distributions generated by this algorithm can be used to make comparisons of various inferential procedures that are free from Monte Carlo sampling errors. In this paper, these two features of the algorithm are utilized to compare small-sample properties of the exact, mid-P value, and score tests for a conditional logistic model with two unmatched binary covariates. Both uniparametric and multiparametric tests, performed at a nominal significance level of .05, were studied. It was found that the actual significance levels of the mid-P test tend to be closer to the nominal level when compared with those of the other two tests.
Algorithms↗
A note on interrater agreement.
We investigate the properties of a measure of interrater agreement originally proposed by Rogot and Goldberg. Unlike commonly used measures, this measure not only adjusts for chance agreement, but it also standardizes for both perfect agreement as well as for perfect disagreement. Further, one can also use this measure to assess category specific conditional agreement, and thus apply it to situations with missing main diagonal data. We provide an asymptotic method for inference with this measure.
Autoantibodies↗
Efficacy of intensive chemotherapy for acute myelogenous leukemia associated with a preleukemic syndrome.
One hundred ninety-six patients with acute myelogenous leukemia (AML) were treated with intensive induction chemotherapy using similar daunorubicin/cytarabine/thioguanine regimens. Treatment results of 44 patients who had a documented preleukemic syndrome or cytopenia present for more than 2 months before developing over AML were compared with 152 patients with de novo AML. Eighteen (41%) patients with preleukemia evolving into AML achieved complete remission compared with 111 (73%) patients with de novo AML (P less than .01). Patients with preleukemia-AML had a significantly longer period to recovery of granulocytes. Multivariate analysis indicated that presence of a previous preleukemic syndrome and advancing age were independent poor prognostic indicators for achieving remission. For patients who achieved remission, disease-free survival and overall survival were also inferior for patients with previous preleukemia; disease-free survival was 17 +/- 17% at 3 years compared with 29 +/- 10% in patients with de novo AML (P = .02). These data indicate that intensive chemotherapy has limited efficacy in patients with AML following a preleukemic syndrome. Durable remissions may be achieved in some patients.
Age Factors↗
Exact versus asymptotic analysis for a matched case-control study.
We compare exact and asymptotic methods for variable selection in matched case-control studies. Data from a study of melanoma among the employees of the Lawrence Livermore National Laboratory illustrate the comparisons. Relative to large sample methods, the exact method almost always yielded larger p-values. The differences in p-values became more pronounced with inclusion of more variables in the logistic model. Thus, when the sample size is not large, and there are many covariates under study, use of the exact method tends to select more parsimonious models and avoids overfit of the data.
Algorithms↗
Exact inference for matched case-control studies.
In an epidemiological study with a small sample size or a sparse data structure, the use of an asymptotic method of analysis may not be appropriate. In this paper we present an alternative method of analyzing data for case-control studies with a matched design that does not rely on large-sample assumptions. A recursive algorithm to compute the exact distribution of the conditional sufficient statistics of the parameters of the logistic model for such a design is given. This distribution can be used to perform exact inference on model parameters, the methodology of which is outlined. To illustrate the exact method, and compare it with the conventional asymptotic method, analyses of data from two case-control studies are also presented.
Algorithms↗