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N Klar

Publications and source records attributed to N Klar.

At least 19 recordsLinked to original sources
PubMed2007

Developments in cluster randomized trials and Statistics in Medicine.

The design and analysis of cluster randomized trials has been a recurrent theme in Statistics in Medicine since the early volumes. In celebration of 25 years of Statistics in Medicine, this paper reviews recent developments, particularly those that featured in the journal. Issues in design such as sample size calculations, matched paired designs, cohort versus cross-sectional designs, and practical design problems are covered. Developments in analysis include modification of robust methods to cope with small numbers of clusters, generalized estimation equations, population averaged and cluster specific models. Finally, issues on presenting data, some other clustering issues and the general problem of evaluating complex interventions are briefly mentioned.

Bayes Theorem↗
PubMed2004

Breast screening outcomes in women with and without a family history of breast and/or ovarian cancer.

OBJECTIVES: To compare breast screening outcomes between women with a moderate or strong family history of breast and/or ovarian cancer with those without such a history. SETTING: The Ontario Breast Screening Programme (OBSP) is a population-based programme offering mammography and clinical breast examination to Ontario women of 50 and older. METHODS: Data from a cohort of 143,574 women screened by the OBSP from 1996 to 1997 were included. Referral rates, cancer detection rates, positive predictive values and the histological features of screen-detected cancers were examined within family history groups, age groups and screening modalities. Logistic regression analysis of cancer detection was conducted to adjust for potential confounding variables; subgroup analysis by hormone replacement therapy (HRT) use was also undertaken. RESULTS: Compared with women with no family history, women with a moderate or strong family history of breast and/or ovarian cancer were more likely to have their cancer detected (odds ratio [OR]=1.44, 95% confidence interval [CI] 1.20-1.74 and OR=1.42, 95% CI 1.10-1.83, respectively). Among women using HRT, however, there was no association observed between family history and cancer detection (moderate: OR=0.98, 95% CI 0.65-1.48; strong: OR=1.17, 95% CI 0.68-2.02) with history. The histological features of invasive tumours were similar among family history groups. CONCLUSIONS: Greater cancer detection rates and high proportions of invasive tumours with good prognosis indicate that women aged 50 and over with a family history may have the potential to benefit from regular breast cancer screening. Further studies are required to identify optimal screening guidelines and to examine whether HRT reduces the ability to detect cancer in these women.

Breast Neoplasms↗
PubMed2003

Lymph node retrieval and assessment in stage II colorectal cancer: a population-based study.

BACKGROUND: Adjuvant chemotherapy for patients with stage III (node-positive) colorectal cancer (CRC) reduces mortality by one third. Retrieval of an inadequate number of lymph nodes in the surgical specimen may result in incorrectly designating some patients as stage II (node negative), and consequently, such patients may not be offered appropriate chemotherapy. Recent National Cancer Institute guidelines suggest that a minimum of 12 nodes should be examined to ensure accurate staging. METHODS: This population-based study identified stage II (T3N0 and T4N0) CRC cases by using CRC pathology reports (1997-2000) from the Ontario Cancer Registry. Patients aged 19 to 75 years were identified, and demographic, surgical, pathologic, and hospital data were extracted. Factors relating to the number of lymph nodes assessed were examined. RESULTS: A total of 8848 CRC cases were reviewed, and 1789 stage II cases were identified. Seventy-three percent of cases were designated as node negative on the basis of assessment of <12 lymph nodes. Multivariate analysis showed that age, tumor size, specimen length, use of a pathology template, and academic status of the hospital were significant predictors of the number of lymph nodes assessed. CONCLUSIONS: A subset of patients with CRC in Ontario were assigned stage II disease on the basis of examination of relatively few lymph nodes.

Adult↗
PubMed2001

Current and future challenges in the design and analysis of cluster randomization trials.

Randomized trials in which the unit of randomization is a community, worksite, school or family are becoming widely used in the evaluation of life-style interventions for the prevention of disease. The increasing interest in adopting a cluster randomization design is being matched by rapid methodological developments. In this paper we describe several of these developments. Brief mention is also made of issues related to economic analysis and to the planning and conduct of meta-analyses for cluster randomization trials. Recommendations for reporting are also discussed.

Adult↗
PubMed2001

Nipple fluid carcinoembryonic antigen and prostate-specific antigen in cancer-bearing and tumor-free breasts.

PURPOSE: Mammograms and breast examinations are established methods for early breast cancer detection. Routine mammography screening reduces breast cancer mortality among women ages > or = 50 years, but additional screening methods are needed. We and others have found high levels of carcinoembryonic antigen (CEA) and prostate-specific antigen (PSA) in nipple aspirate fluids (NAFs), but the usefulness for these bio-markers for early breast cancer detection is unknown. PATIENTS AND METHODS: NAFs from one or both breasts of 388 women were analyzed for CEA, PSA, and albumin levels. The study included 44 women with newly diagnosed invasive breast cancers, 67 women with proliferative breast lesions (ductal and lobular carcinoma in situ and atypical ductal hyperplasia), and 277 controls without these breast lesions. Analyses were conducted using the log(10)-transformed CEA and PSA levels to normalize the distributions of these tumor markers. RESULTS: Nipple fluid CEAs are significantly higher for cancerous breasts than tumor-free breasts (median 1,830 and 1,400 ng/mL, respectively; P <.01). However, at 90% specificity of the assay (CEA = 11,750 ng/mL), the corresponding sensitivity for cancer detection is 32%. CEA levels are not significantly different for breasts with proliferative lesions compared with tumor-free breasts. Nipple fluid PSAs do not differ by tumor status. Analyses of NAF albumin-standardized CEAs and PSAs yield similar results. Nipple fluid CEA and PSA titers are correlated in the affected and unaffected breast of women with unilateral lesions. CONCLUSION: Nipple fluid CEAs are higher for breasts with untreated invasive cancers, but the test sensitivity is low. Nipple fluid PSA titers do not seem to be useful for breast cancer detection.

Adult↗
PubMed2001

Inference procedures for assessing interobserver agreement among multiple raters.

We propose a new procedure for constructing inferences about a measure of interobserver agreement in studies involving a binary outcome and multiple raters. The proposed procedure, based on a chi-square goodness-of-fit test as applied to the correlated binomial model (Bahadur, 1961, in Studies in Item Analysis and Prediction, 158-176), is an extension of the goodness-of-fit procedure developed by Donner and Eliasziw (1992, Statistics in Medicine 11, 1511-1519) for the case of two raters. The new procedure is shown to provide confidence-interval coverage levels that are close to nominal over a wide range of parameter combinations. The procedure also provides a sample-size formula that may be used to determine the required number of subjects and raters for such studies.

Binomial Distribution↗
PubMed2000

Disclosure of familial genetic information: perceptions of the duty to inform.

BACKGROUND: The familial implications of genetic information can lead to a conflict between a physician's duties to maintain patient confidentiality and to inform at-risk relatives about susceptibility to genetic diseases. As genes are discovered that can identify patients at risk of adverse outcomes, this conflict has become the subject of discussion and debate. METHODS: We performed a one-time telephone survey of a population-based sample of 200 Jewish women to assess knowledge and attitudes about genetic testing. Attitudes toward sharing genetic test results with family members were evaluated using three hypothetical scenarios that described an easily preventable disease, a disease (breast cancer) in which the only option for prevention was prophylactic mastectomies, and a nonpreventable disease. RESULTS: Nearly all respondents believed that a patient should inform at-risk family members when the disease was preventable (100% and 97% in the relevant scenarios), compared with only 85% who felt a duty to inform at-risk family members about a nonpreventable disease (P <0.001). The proportions of respondents who believed that physicians should seek out and inform at-risk family members against a patient's wishes was much lower: only 18% of respondents to the easily preventable disease scenario, 22% of respondents to the breast cancer scenario, and 16% of respondents to the nonpreventable disease scenario. CONCLUSIONS: Most women surveyed believed that genetic information should be shared within families, unless it violated a patient's wishes. These sorts of opinions should be considered in the debate over the confidentiality of genetic information.

Adult↗
PubMed2000

Understanding of prognosis among parents of children who died of cancer: impact on treatment goals and integration of palliative care.

CONTEXT: Parents' understanding of prognosis or decision making about palliative care for children who die of cancer is largely unknown. However, a more accurate understanding of prognosis could alter treatment goals and expectations and lead to more effective care. OBJECTIVES: To evaluate parental understanding of prognosis in children who die of cancer and to assess the association of this factor with treatment goals and the palliative care received by children. DESIGN, SETTING, AND PARTICIPANTS: Survey, conducted between September 1997 and August 1998, of 103 parents of children who received treatment at the Dana-Farber Cancer Institute and Children's Hospital, Boston, Mass, and who died of cancer between 1990 and 1997 (72% of those eligible and those located) and 42 pediatric oncologists. MAIN OUTCOME MEASURE: Timing of parental understanding that the child had no realistic chance for cure compared with the timing of physician understanding of this prognosis, as documented in the medical record. RESULTS: Parents first recognized that the child had no realistic chance for cure a mean (SD) of 106 (150) days before the child's death, while physician recognition occurred earlier at 206 (330) days before death. Among children who died of progressive disease, the group characterized by earlier recognition of this prognosis by both parents and physicians had earlier discussions of hospice care (odds ratio [OR], 1.03; 95% confidence interval [CI], 1.01-1.06; P =.01), better parental ratings of the quality of home care (OR, 3.31; 95% CI, 1.15-9.54; P =.03), earlier institution of a do-not-resuscitate order (OR, 1.03; 95% CI, 1.00-1.06; P =.02), less use of cancer-directed therapy during the last month of life (OR, 2.80; 95% CI, 1.05-7.50; P =.04), and higher likelihood that the goal of cancer-directed therapy identified by both physician and parent was to lessen suffering (OR, 5.17; 95% CI, 1.86-14.4; P =.002 for physician and OR, 6.56; 95% CI, 1.54-27.86; P =.01 for parents). CONCLUSION: Considerable delay exists in parental recognition that children have no realistic chance for cure, but earlier recognition of this prognosis by both physicians and parents is associated with a stronger emphasis on treatment directed at lessening suffering and greater integration of palliative care. JAMA. 2000;284:2469-2475.

Adult↗
PubMed2000

Testing the equality of two dependent kappa statistics.

Procedures are developed and compared for testing the equality of two dependent kappa statistics in the case of two raters and a dichotomous outcome variable. Such problems may arise when each of a sample of subjects are rated under two distinct settings, and it is of interest to compare the observed levels of inter-observer and intra-observer agreement. The procedures compared are extensions of previously developed procedures for comparing kappa statistics computed from independent samples. The results of a Monte Carlo simulation show that adjusting for the dependency between samples tends to be worthwhile only if the between-setting correlation is comparable in magnitude to the within-setting correlations. In this case, a goodness-of-fit procedure that takes into account the dependency between samples is recommended.

Analysis of Variance↗
PubMed2000

Symptoms and suffering at the end of life in children with cancer.

BACKGROUND: Cancer is the second leading cause of death in children, after accidents. Little is known, however, about the symptoms and suffering at the end of life in children with cancer. METHODS: In 1997 and 1998, we interviewed the parents of children who had died of cancer between 1990 and 1997 and who were cared for at Children's Hospital, the Dana-Farber Cancer Institute, or both. Additional data were obtained by reviewing medical records. RESULTS: Of 165 eligible parents, we interviewed 103 (62 percent), 98 by telephone and 5 in person. The interviews were conducted a mean (+/-SD) of 3.1+/-1.6 years after the death of the child. Almost 80 percent died of progressive disease, and the rest died of treatment-related complications. Forty-nine percent of the children died in the hospital; nearly half of these deaths occurred in the intensive care unit. According to the parents, 89 percent of the children suffered "a lot" or "a great deal" from at least one symptom in their last month of life, most commonly pain, fatigue, or dyspnea. Of the children who were treated for specific symptoms, treatment was successful in 27 percent of those with pain and 16 percent of those with dyspnea. On the basis of a review of the medical records, parents were significantly more likely than physicians to report that their child had fatigue, poor appetite, constipation, and diarrhea. Suffering from pain was more likely in children whose parents reported that the physician was not actively involved in providing end-of-life care (odds ratio, 2.6; 95 percent confidence interval, 1.0 to 6.7). CONCLUSIONS: Children who die of cancer receive aggressive treatment at the end of life. Many have substantial suffering in the last month of life, and attempts to control their symptoms are often unsuccessful. Greater attention must be paid to palliative care for children who are dying of cancer.

Anorexia↗
PubMed2000

Analysis of dichotomous outcome data for community intervention studies.

Community intervention trials are becoming increasingly popular as a tool for evaluating the effectiveness of health education and intervention strategies. Typically, units such as households, schools, towns, counties, are randomized to receive either intervention or control, then outcomes are measured on individuals within each of the units of randomization. It is well recognized that the design and analysis of such studies must account for the clustering of subjects within the units of randomization. Furthermore, there are usually both subject level and cluster level covariates that must be considered in the modelling process. While suitable methods are available for continuous outcomes, data analysis is more complicated when dichotomous outcomes are measured on each subject. This paper will compare and contrast several of the available methods that can be applied in such settings, including random effects models, generalized estimating equations and methods based on the calculation of 'design effects', as implemented in the computer package SUDAAN. For completeness, the paper will also compare these methods of analysis with more simplistic approaches based on the summary statistics. All the methods will be applied to a case study based on an adolescent anti-smoking intervention in Australia. The paper concludes with some general discussion and recommendations for routine design and analysis.

Adolescent↗
PubMed2000

Predicting costs of stem-cell transplantation.

PURPOSE: Few studies have formally evaluated the relationship between costs, baseline patient characteristics, and major complications of stem-cell transplantation. We sought (1) to determine whether obtaining baseline information enabled identification of patients whose treatments would be the most costly and (2) to estimate inpatient costs for managing specific transplantation complications. PATIENTS AND METHODS: We collected inpatient costs and clinical information for 236 consecutive patients undergoing transplantation at a single institution between July 1, 1994, and February 20, 1997. Multivariable linear regression was used to evaluate the associations between baseline patient characteristics and costs of hospitalization for initial transplantation and between clinical events and such costs. RESULTS: The median initial inpatient cost in 1997 dollars was $55,500 for autologous transplantation (range, $28,200 to $148,200) and $105,300 for allogeneic transplantation (range, $32,500 to $338,000). When only baseline variables were considered, use of a mismatched allogeneic donor and year of transplantation were significant predictors of costs. No characteristics predicted which patients would incur the highest 10% of costs. When clinical events were considered, infection and in-hospital death were associated with higher costs in autologous transplant recipients ($18,400 and $20,500, respectively), whereas infection, veno-occlusive disease, acute graft-versus-host disease, and death were predicted to add between $15,300 and $28,100 each to allogeneic transplantation costs. CONCLUSION: We were not able to identify before transplantation the patients whose treatments would be the most costly. However, the association between clinical complications and higher costs suggests that prevention may have significant economic benefits. Interventions that decrease these complications may have favorable cost-benefit ratios even if they do not affect overall survival.

Adolescent↗
PubMed2000

Behavioral risk factors among women presenting for genetic testing.

Considerable research attention has been given to the impact of genetic testing on psychological outcomes. Participation in genetic testing also may impact on health behaviors that increase the risk of cancer and other chronic diseases. The purpose of this study is to describe behavioral cancer risk factors of women who requested genetic testing for breast and ovarian cancer susceptibility (BRCA1, BRCA2). Before participation in a genetic testing program, 119 women completed a series of questionnaires designed to assess their health behaviors, perception of risk, and depressive symptomatology. Eight percent of participants were current smokers, 27% did not engage in at least moderate exercise, 46% did not regularly protect themselves from the sun, 39% did not consume at least five servings of fruits and vegetables per day, and 9% drank at least one alcoholic beverage per day. Poisson regression analysis revealed that age was the only predictor of behavioral risk profiles, with older women having fewer cancer risk behaviors. These patients who presented for genetic testing generally had better health behaviors than the general population. However, given their possible high-risk status, these patients should consider further improving their preventable cancer risk factors and, in particular, their diet, sun protection, and physical activity levels. Inclusion of behavioral risk factor counseling in the context of the genetic testing process may be an important opportunity to reach this at-risk population.

Adult↗
PubMed1999

Testing the equality of twin correlations with multinomial outcomes.

Twin studies are widely used to study genetic and environmental influences on human measurements. Correlations are often used in such studies to compare the levels of similarity between monozygotic and dizygotic twins with respect to a specified trait. In this paper, we compare three procedures for testing the equality of twin correlations when the outcome variable of interest is multinominal. One method is a likelihood ratio test based on an underlying Dirichlet-multinomial distribution. The second method is based on the estimated large sample variance of the estimated correlation, and the third method is based on a chi 2 goodness-of-fit test. The results of a Monte Carlo simulation show that the three methods have similar properties if the number of twin pairs is large (> 100), and the prevalence of the underlying trait is not extreme. Otherwise, the goodness-of-fit approach is to be preferred. We illustrate the methods by analyzing data from a previously published smoking study.

Analysis of Variance↗
PubMed1997

The merits of matching in community intervention trials: a cautionary tale.

Concern about potential imbalance on risk factors in community intervention trials often prompts researchers to adopt a pair-matched design in which similar clusters of individuals are paired and one member of each matched pair is then randomly assigned to the intervention group. It is known that if there are few clusters in trial, it becomes increasingly difficult to obtain close matches on all potential risk factors. One may thus offset any gain in precision with loss in degrees of freedom due to matching. We shown in this paper that there are also several analytic limitations with pair-matched designs. These include: the restriction of prediction models to cluster-level baseline risk factors (for example, cluster size), the inability to test for homogeneity of odds ratios, and difficulties in estimating the intracluster correlation coefficient. These limitations lead us to present arguments that favour stratified designs in which there are more than two clusters in each stratum.

Cluster Analysis↗
PubMed1997

Comparison of methods for analyzing binary data arising from two-sample twin studies.

The study of twins is widely used for research into genetic and environmental influences on human outcome measurements. For the study design in which independent samples of monozygotic and dizygotic twins are compared with respect to their similarity on a binary trait, several statistical methods have been proposed. Using a Monte Carlo simulation, we compare the five following procedures: 1) goodness-of-fit method based on the common correlation model, 2) normal approximation of the maximum likelihood estimators of the common correlation coefficients, 3) Ramakrishnan et al. [(1992) Genet Epidemiol 9:273-282] method of odds ratio comparison, 4) generalized estimating equations method of odds ratio estimation, and 5) tetrachoric correlation method. The results show that the goodness-of-fit approach has similar or better performance in both type-one error rates and power than the other methods in all parameter settings. Its advantage with respect to type-one error rates is particularly clear under conditions of small sample sizes, extreme prevalences, or high values of the intraclass correlation coefficients. Therefore, the goodness-of-fit method is recommended for the two-sample twin study design.

Coronary Disease↗
PubMed1996

Statistical considerations in the design and analysis of community intervention trials.

Community intervention trials are often characterized by the allocation of intact social units to different intervention groups. The assessment of adequate sample size for such trials must take into account the statistical dependencies among responses observed within an allocated unit. However, the small numbers of units typically involved in such trials imply that many methods of analysis that have been proposed for analyzing correlated data, particularly in the case of a dichotomous outcome variable, are not applicable to such designs. In this article we investigate this issue and determine the minimum number of units required per group, for the case of both a dichotomous and a continuous outcome variable, needed to provide adequate statistical power for detecting various levels of treatment effect. The use of significance testing as a method of detecting intracluster correlation is also investigated, and, in general, discouraged.

Adolescent↗