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Biomedical subjects

M Zelen

Publications and source records attributed to M Zelen.

At least 19 recordsLinked to original sources
PubMed1998

Urn sampling and the proportional hazard model.

This paper investigates the urn sampling analogue for the score statistic relating survival to covariates assuming a proportional hazard model. The exact permutation distribution can be calculated as well as the exact low order moments for arbitrary censoring patterns. The asymptotic distribution of the score statistic is an easy consequence. The method is naturally extended to deal with the multivariate case, time varying covariates and interval censoring. Finally the relationship between the censoring process, the survival times and covariates are studied considering different reference sets for the distribution of the score statistic. Some assumptions about the censoring process are investigated and as a consequence the effect of censoring is clarified.

Biometry↗
PubMed1998

Milk leakage in nonlactating women: a randomized clinical trial evaluating a polyvinyl chloride device versus disposable breast pads.

A randomized clinical trial was carried out to evaluate the safety and helpfulness of the LactaPrev System (LPS) compared with disposable pads for milk leakage management for postpartum, nonlactating women (those who do not breastfeed). Fifty-five women completed the single-blind, randomized trial. Participants wore each device on each breast concurrently. Assignment of the LPS or pad to each breast was done randomly. Fifty-eight percent of participants preferred the LPS. The longer the participation in the study, which correlated with the duration of milk leakage, the greater the preference (p = 0.05). Preference was related to bra size (p = 0.05). The smaller the bra size, the greater the preference for the LPS. There was no greater incidence of complications from the LPS compared with the disposable breast pad.

Adolescent↗
PubMed1997

Managing milk leakage in breastfeeding women: a clinical trial evaluating a polyvinyl chloride device versus disposable nursing pads.

The object of this clinical trial was to evaluate the effectiveness and to investigate possible problems associated with the use of a polyvinyl chloride (PVC) device ("blis") compared to a disposable nursing pad, for controlling milk leakage among nursing mothers. Seventy-one women completed the single blind, paired comparison, randomized trial. Among the 28 women having a strong early preference, 21 opted for the PVC device (p = 0.01). Of the 37 women experiencing excessive milk leakage who preferred one of the devices, 24 preferred the PVC device (p = 0.05). There was no evidence that one device caused more problems or feeding complications than the other. This study is important in alleviating anxiety about device safety while promoting breastfeeding in mothers fearful of leaking at inopportune times.

Adolescent↗
PubMed1995

Intermediate clinical events, surrogate markers and survival.

This paper investigates one- and two-sample problems comparing survival times when an individual may experience an intermediate event prior to death or reaching some well defined endpoint. The intermediate event may be polychotomous. Patients experiencing the intermediate event may have an altered survival distribution after the intermediate event. Score tests are derived for testing if the occurrence of the intermediate event actually alters survival. These models have implications for evaluating therapies without randomization as well as strengthening the log rank test for comparing two survival distributions. The exact distribution of the score tests can be found by conditioning on both the waiting time and occurrence of the intermediate event.

Biomarkers↗
PubMed1990

Randomized consent designs for clinical trials: an update.

Randomized consent designs were introduced to make it easier for physicians to enter patients in randomized clinical trials. Physician reluctance to participate in randomized clinical trials is often a reflection that the physician-patient relationship could be compromised if the physician makes known to the patient his/her inability to select a preferred therapy. Clinical trials having a no-treatment control or placebo amplify this concern. This paper reviews the main ideas of randomized consent designs (single and double) and the statistical model underlying the analysis, and presents some recent experiences.

Informed Consent↗
PubMed1989

An investigation of a reported cancer cluster in Randolph, Massachusetts.

An increasingly common public health problem is the perception that disease incidence has increased or a cluster of disease has occurred in a community. In most cases, the disease of concern is cancer and a local hazardous waste site or other environmental problem is involved. These problems can be difficult to investigate and public health officials are frequently criticized for their inability to address community concerns. This paper reports a case study of such a situation occurring in the Barlett-Green Acres (BGA) neighborhood of Randolph, Massachusetts. Study data were obtained by interviews in households of persons belonging to a list of alleged cancer cases initially supplied by residents and supplemented using records available in town and state public health offices. One objective of the investigation was to develop methods that may be of value in similar situations arising in other communities. From a list of names compiled prior to and during the investigation, 45 incident cases of cancer were identified and found suitable for analysis. An additional four cases were added from the Massachusetts Cancer Registry. The analysis showed the existence of a cancer cluster, but overall cancer incidence and mortality in the BGA neighborhood were not elevated. Residence history, disease site, and other features of the cancer cases were investigated using methods less sensitive to incomplete reporting than total incidence. No unusual features of the cancer data other than the initiating cluster were identified and no environmental hazard likely to impact the BGA neighborhood was discovered, hence we conclude that the most likely cause of the cancer cluster was random variation in cancer rates.

Adolescent↗
PubMed1987

State of the art in comparative cancer clinical trials.

In order to investigate the current state of the art in clinical cancer research, a survey of comparative cancer clinical trials was conducted using a MEDLINE literature search of the 6-month interval from July to December of 1985. Data were obtained primarily from the published abstracts. The major observations from the study are as follows. First, trials in cancer research are published in an extraordinarily wide range of journals covering most of the major medical specialties in addition to the many cancer specialty journals. Second, randomization is now used quite extensively. It is the predominant method of control in chemotherapy trials and in trials reported in cancer journals. However, its use is much less common in other specialties, especially surgery, so efforts to popularize randomization in these specialties would be beneficial. Third, sample sizes are highly variable, and the median sample size (96 patients) is too small to reliably detect and evaluate moderate treatment advances. Finally, our survey reveals that published trials show an inordinately large proportion of breakthroughs in treatment compared with the generally accepted view that only slow progress is being made in developing effective cancer treatments. Our view is that this result reflects the strong tendency to publish only studies with positive results. This hypothesis is supported by the fact that in nonrandom trials there tend to be more positive conclusions and an absence of a strong association between conclusions and sample size.

Clinical Trials as Topic↗
PubMed1986

Assessment of adjuvant trials in breast cancer.

In this paper, we discuss the analytic problems associated with the evaluation of overall survival for breast cancer adjuvant studies and results of pooling data from the published literature to determine if there is evidence showing an overall survival advantage to adjuvant therapy. An investigation of the effect of competing causes of death shows that trials on older patients have low statistical power. Hence many of the current trials have low statistical power and may fail to find overall survival advantage for adjuvant therapy even when a benefit exists. The implications of the assessment of short-term follow-up are discussed in the context of the heterogeneous distribution of residual disease after primary treatment. Short-term follow-up (less than 5 yr) precludes anyone from making any conclusions about benefit for patients with small residual tumor burdens who constitute the patient subgroup most likely to benefit from adjuvant therapy. We reviewed 15 published randomized trials (each having a control group receiving no systemic therapy) to determine if overall survival has been increased by adjuvant therapy. We conclude that there is a benefit from some chemotherapy regimens given to node-positive premenopausal women. However, the published data for tamoxifen are mixed, with some trials showing benefit and others not. As more follow-up time is accumulated, this matter should be settled.

Adult↗
PubMed1985

Exploratory data analysis and the use of the hazard function for interpreting survival data: an investigator's primer.

This report discusses how one can use the hazard function to gain important insights on the patterns of failure in clinical studies when the principal endpoint is a time metric. These new insights may help gain increased understanding into the pathogenesis of a chronic disease and how it is affected by treatment intervention. The qualitative behavior of the hazard function can reveal whether mortality is increasing, decreasing, or is constant over time. Simple graphic plots are all that is necessary to show characteristic failure patterns. These informal procedures are in the spirit of carrying out exploratory analyses on the data. This report discusses the organization of clinical data using a "branch and leaf" plot, outlines the calculation of the hazard function and life table, and uses examples from lung cancer and uveal melanoma to illustrate calculations and ways of interpreting hazard functions.

Adenocarcinoma↗
PubMed1985

Products liability issues in school asbestos litigation.

The hazards posed by deteriorating friable asbestos in the nation's schools are causing serious concerns for public health officials, school boards, parents and school employees. Reports by both the Environmental Protection Agency and the U.S. Attorney General's Office agree that both school children and school employees stand a substantially increased risk of contracting some form of asbestos-related disease as a result of exposure to deteriorating asbestos materials in school buildings. School systems plagued by the asbestos hazards are now filing suits against asbestos manufacturers alleging causes of action in breach of warranty, negligence and strict products liability in tort. Some plaintiffs in school asbestos litigation seek to recover the costs of EPA-mandated asbestos inspection and abatement programs which have already been completed. Still others request injunctions to compel the manufacturers themselves to conduct inspections and finance abatement. This Note examines the school asbestos situation from a legal perspective and focuses primarily on whether the schools' claims should be considered as economic losses or as property damage. It examines the impact of statutes of limitations on these cases under both contract and tort theories. The Note argues that school asbestos claims should be decided under a strict products liability standard.

Adult↗
PubMed1984

Inferring the natural time history of breast cancer: implications for tumor growth rate and early detection.

This review analyzes the results of 692 breast cancer patients from the Norwegian Radium Hospital. All cases were diagnosed during the period 1951-1959 and the average follow-up time was just under eight years. All patients received a radical mastectomy and had their diagnoses pathologically confirmed by a separate reviewer. The purpose of this paper is to apply a novel method of analysis in order to infer the longitudinal course of the disease as if it had not been interrupted by treatment. The method allows one to estimate the average times between changes in the biological factors which characterize the natural history of the disease. Applying this method to the Norwegian data has resulted in identifying three pathways of the natural history of the disease. The tumor growth rates differ for these pathways and are in the approximate ratio 1:5:27. Furthermore, we can estimate the potential benefit from earlier diagnosis. Two of the three pathways would seem to benefit from earlier detection.

Adult↗