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Biomedical subjects

R J Hardy

Publications and source records attributed to R J Hardy.

At least 73 records · Page 4Linked to original sources
PubMed1991

Operational aspects of terminating randomization in the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity. Cryotherapy for Retinopathy of Prematurity Cooperative Group.

The Multicenter Trial of Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) is a randomized clinical trial sponsored by the National Eye Institute (NEI) designed to test whether cryotherapy applied to eyes of premature infants with a specified extent of stage 3+ ROP significantly decreases the incidence of an unfavorable outcome. An unfavorable outcome is defined as either retinal detachment or a retinal fold and was determined at 3 months posttreatment by the use of a masked photographic system. Enrollment into the trial was terminated on recommendation of the Data and Safety Monitoring Committee 9 months before the scheduled closing date for enrollment because of demonstrated treatment benefit. The purpose of this article is to discuss the operations involved in the orderly termination of enrollment and dissemination of results from this trial. These activities included preparation of trial participants and staff, release of trial information, continuing patient care, data collection and coding, and publication of trial results.

Blindness↗
PubMed1991

Statistical considerations in terminating randomization in the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity. Cryotherapy for Retinopathy of Prematurity Cooperative Group.

The Multicenter Trial of Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) was a randomized trial designed to test whether cryotherapy applied to the retina significantly decreased the incidence of retinal detachment, retinal fold, or retrolental "mass." Randomization into the trial was terminated on recommendation of the Data and Safety Monitoring Committee 9 months before the scheduled end of the intake period. At the time of the decision, a favorable outcome at 3 months posttreatment occurred more frequently in eyes treated with cryotherapy (78%) as compared to untreated eyes (57%) (chi 2 = 20.5). The basic statistical method used in monitoring the results was conditional power (or stochastic curtailment). Several other issues were considered in deciding to terminate the trial, including the examination of results across subgroups and clinical centers, the completeness of follow-up, clinical assessment of outcome, and long-term consequences of the treatment.

Bias↗
PubMed1991

Incidence and early course of retinopathy of prematurity. The Cryotherapy for Retinopathy of Prematurity Cooperative Group.

In the Multicenter Trial of Cryotherapy for Retinopathy of Prematurity (ROP), 4099 infants weighing less than 1251 g at birth underwent sequential ophthalmic examinations, beginning at age 4 to 6 weeks, to monitor the incidence and course of ROP. Overall, 65.8% of the infants developed ROP to some degree; 81.6% for infants of less than 1000 g birth weight. As expected, ROP incidence and severity were higher in lower birth weight and gestational age categories. Black infants appeared less susceptible to ROP, of all severity categories, than nonblack infants. The timing of retinal vascular events correlated more closely with postconceptional age than with postnatal age, implicating the level of maturity more than postnatal environmental influences in governing the timing of these vascular events. These results include the current incidence of various severity stages of ROP found in the United States and provide new insight into the development of ROP.

Cryosurgery↗
PubMed1990

A surveillance system for assessing health effects from hazardous exposures.

A statistical procedure for monitoring the health status of a community potentially exposed to a hazardous environment is presented. It utilizes two levels of investigation. Level I studies monitor routinely collected vital statistics and routes of community exposure whereas level II studies require additional data collection and are further distinguished by their design and duration. In a level I study, routine vital statistics for specified end points over a specified period of time are monitored, and the observed number of events is compared with the expected number of events for a given population. The statistical model used with this procedure employs a two-step decision rule based on the standardized mortality ratio for the study community. An "alert status" is invoked when the number of events exceeds a prescribed excess. An "action status" is indicated if the excess noted in the initial period persists or if the observed number of events in the initial period greatly exceeds expectation. Should an "action status" be justified, level II studies to determine the likely explanation for the significant excess are initiated. This could include the conduct of a "case-control" study using the exposure data available from monitoring the community.

Cluster Analysis↗
PubMed1989

An illness-death process with time-dependent covariates.

A general model for the illness-death stochastic process with covariates has been developed for the analysis of survival data. This model incorporates important baseline and time-dependent covariates in order to make an appropriate adjustment for the transition and survival probabilities. The follow-up period is subdivided into small intervals and a constant hazard is assumed for each interval. An approximation formula is derived to estimate the transition parameters when the exact transition time is unknown. The method developed is illustrated with data from a study on the prevention of the recurrence of a myocardial infarction and subsequent mortality, the Beta-Blocker Heart Attack Trial (BHAT). This method provides an analytical approach with which the effectiveness of the treatment can be compared between the placebo and propranolol treatment groups with respect to fatal and nonfatal events simultaneously.

Biometry↗
PubMed1988

Lung cancer mortality among women employed in high-risk industries and occupations in Harris County, Texas, 1977-1980.

Lung cancer is rapidly becoming the leading cause of cancer mortality among women. Interviews conducted with 259 women with lung cancer and 278 women without lung cancer or with their next-of-kin in Harris County, Texas from July 1, 1977 to June 30, 1980 revealed that 12 (4.6%) of the women with lung cancer had never smoked cigarettes. The odds ratio (OR) for current smoking was 15.7. Odds ratios for smoking for living women (OR = 17.5) were higher than for those who were deceased (OR = 12.6). Lifetime occupational histories were classified a priori into high- and low-risk categories. Data were stratified according to employment in a high-risk industry or occupation, a high-risk industry, a high-risk occupation, or both a high-risk industry and occupation. Although not statistically significant, odds ratios for employment in high-risk categories support earlier estimates that attributed 5% of lung cancer mortality in women to employment in hazardous occupations. Employment of a husband or household member in selected industries and occupations yielded significantly increased odds ratios. More cases (15.9%) than controls (6.9%) reported a family history of lung cancer (OR = 2.4). No significant increase in smoking-adjusted odds ratios was found for the use of hair spray, hand-held dryers, or alcohol, or for having lived with a household member who smoked cigarettes.

Adenocarcinoma↗
PubMed1988

The relation between degree of blood pressure reduction and mortality among hypertensives in the Hypertension Detection and Follow-Up Program.

The relation between degree of diastolic blood pressure reduction and mortality was examined among hypertensive persons in the Hypertension Detection and Follow-up Program. This program, conducted from 1973-1979, was a multicenter community-based trial, which followed 10,940 hypertensive participants for five years. The one-year annual visit was the first occasion on which change in blood pressure could be measured on all participants. During the subsequent four years of follow-up on 10,053 participants, 568 deaths occurred. With time-dependent life tables and time-dependent Cox life table regression analyses, the existence of a quadratic function which modeled the relation between diastolic blood pressure reduction and mortality was supported, even after adjusting for other risk factors. The minimum mortality hazard ratio, based on a particular model, occurred at a diastolic blood pressure reduction of 26.2 mmHg (standard error = 13.4) in the whole population and 10.0 mmHg (standard error = 5.3) in the baseline diastolic blood pressure stratum 90-104 mmHg. After this reduction, there was a small increase in the risk of death. There was no evidence of the quadratic function after fitting the same model with systolic blood pressure. Methodological issues involved in studying a particular degree of blood pressure reduction were considered. The confidence interval around the change corresponding to the minimum hazard ratio was wide, and the obtained blood pressure level should not be interpreted as a goal for treatment. Blood pressure reduction was attributed not only to pharmacologic therapy but also to regression to the mean, and to other factors unrelated to treatment.

Actuarial Analysis↗
PubMed1988

Air pollution and lung cancer mortality in Harris County, Texas, 1979-1981.

Elevated lung cancer mortality rates in Harris County, Texas compared with other US counties and previously published reports that suggested a causal relation between air pollution and lung cancer in Houston prompted this ecologic analysis. A weighted regression analysis was used to examine the air pollution-lung cancer mortality relation for white males in Harris County, Texas, 1979-1981. The regression model included the following census tract-specific characteristics: median age for white males, two social and demographic factors not strongly correlated with pollution (family life cycle and migration), an age-dependent smoking index, and a pollution measure based on total suspended particulates. This model indicated a statistically significant contribution of the pollution measure in explaining the intracounty variation in lung cancer mortality rates. The relation between air pollution and lung cancer mortality, however, appeared to be highly dependent on which social and demographic factors were selected for inclusion in the analysis. Air pollution was not demonstrated to be a strong determinant of lung cancer mortality in this study in that the presence of air pollution accounted for less than 5% of the total variation in intraurban lung cancer mortality. In addition, the interpretation of geographic analysis must be guarded due to the introduction of potential bias due to aggregation. The hypothesis that air pollution is contributory to lung cancer cannot be tested until other, stronger individual risk factors for lung cancer can be better measured and controlled in studies of this association.

Adult↗
PubMed1987

Incidence of pelvic endometriosis in Rochester, Minnesota, 1970-1979.

To the authors' knowledge, the incidence pelvic endometriosis in the general female population has not been previously reported. The purpose of the present study was to determine the incidence rate of diagnosed pelvic endometriosis among white females of reproductive age (15-49 years) in Rochester, Minnesota, during 1970-1979. Incidence rates were prepared first with histologically confirmed cases alone and then with the successive inclusion of progressively less certain cases: surgically visualized, clinically probable, and clinically possible. The overall incidence of pelvic endometriosis more than doubled (from 108.8 to 246.9 cases per 100,000 person-years) as the definition of a case was extended from histologically confirmed cases alone to all cases. Age-specific incidence rates increased in successive age groups through age 44 and then declined for women 45-49 years of age. Methodological problems in the definition and ascertainment of incident cases of pelvic endometriosis are described in detail.

Adolescent↗
PubMed1987

A ten year study of partial mastectomy for carcinoma of the breast.

Since 1970, 334 patients have undergone partial mastectomy, axillary dissection and irradiation for treatment of invasive carcinoma of the breast. The average follow-up period is 59 months. Survival curves were calculated for the entire study group and for patients classified by tumor size, nodal status and stage of disease. The five year over-all survival rate for 334 patients is approximately 87 per cent; the ten year survival rate is approximately 64 per cent. Of the 334 patients, 247 (74 per cent) have been observed for at least two years. Fourteen of these patients (5.7 per cent) have had a recurrence of carcinoma develop within the treated breast.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1985

A computer program for an illness-death process with time-dependent covariates.

This paper presents a computer program for estimating transition probabilities between states in a stochastic model for an illness-death process which incorporates time-dependent covariates. Parameters are estimated by the method of maximum likelihood using the Newton-Raphson iterative procedure. The program provides the standard normal deviate statistics as well as the value of the maximum of the likelihood function which can be used on repeated applications to test hypotheses concerning coefficients associated with covariates. Although this program is demonstrated by using a model with two 'illness' states and two 'death' states, it is also suitable for analyzing data with models involving fewer states, such as the analysis of survival time with covariates assuming a proportional hazard model.

Computers↗
PubMed1983

Serum cholesterol and cancer in the Hypertension Detection and Follow-up Program.

The relation between serum cholesterol and cancer incidence was investigated in the population of the Hypertension Detection and Follow-up Program. During the 5 years of follow-up, 286 new cancer cases were documented among the 10,940 participants. Overall, age-adjusted cancer incidence rates, computed by baseline serum cholesterol quartiles, showed a small, but statistically significant, inverse relation between serum cholesterol and cancer incidence. No evidence suggested that the observed relationship was primarily due to confounding by other cancer risk factors, association of low serum cholesterol with incipient but undiagnosed cancer, or problems of competing risks. However, the relationship is weak and a causal interpretation of these immediate results cannot be argued persuasively. Examinations of specific cancer sites and factors related to serum cholesterol are suggested as important lines of research toward clarification of the complex relationships observed.

Adult↗
PubMed1983

The impact of selected indices of antihypertensive treatment on all-cause mortality.

Two important questions regarding the results of the Hypertension Detection and Follow-up Program are: 1) how much of the difference in mortality between stepped care and referred care can be attributed to treatment for hypertension, and 2) was there a relationship between treatment of hypertension in the program and the risk of subsequent mortality of the participants? Neither of these questions can be answered within the original randomization scheme of the Hypertension Detection and Follow-up Program; however, statistical techniques can address these two questions. Crude analyses of blood pressures of survivors and deaths in each year of follow-up indicate that survivors had lower blood pressure than persons dying during the interval. An analysis using life table regression with time-dependent covariates suggests that well over half of the excess risk in the referred care group can be attributed to differences in factors related to hypertension treatment. Simultaneously testing the coefficients of the time-dependent variables (diastolic and systolic pressures, blood pressure goal, and medication status) suggests a highly significant relationship between these variables and the risk of subsequent mortality.

Adult↗
PubMed1983

Nuclear magnetic resonance imaging of the spine.

Forty subjects were examined to determine the accuracy and clinical usefulness of nuclear magnetic resonance (NMR) examination of the spine. The NMR images were compared with plain radiographs, high-resolution computed tomograms, and myelograms. The study included 15 patients with normal spinal cord anatomy and 25 patients whose pathological conditions included canal stenosis, herniated discs, metastatic tumors, primary cord tumor, trauma, Chiari malformations, syringomyelia, and developmental disorders. Saturation recovery images were best in differentiating between soft tissue and cerebrospinal fluid. NMR was excellent for the evaluation of the foramen magnum region and is presently the modality of choice for the diagnosis of syringomyelia and Chiari malformation. NMR was accurate in diagnosing spinal cord trauma and spinal canal block. The normal disc was seen, but with rare exceptions bulging of the annulus and herniation of the nucleus pulposus were not visualized.

Adolescent↗
PubMed1980

Two-compartment Markov regression analysis.

This paper presents a computer program for estimating transition rates between states in a two-compartment Markov process, where the rates are functions of covariates. Parameters are estimated by the method of maximum likelihood using the Newton-Raphson iterative procedure. The program provides statistics for testing hypotheses concerning regression coefficients and calculates observed versus expected values in order to assess the fit of the model to the data.

Age Factors↗