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S Lemeshow

Publications and source records attributed to S Lemeshow.

At least 55 records · Page 3Linked to original sources
PubMed1991

Evaluation of a standardized survey design proposed for use in epidemiological research on AIDS.

A Monte Carlo model simulating actual populations was employed to evaluate the precision in estimation of a standardized sampling method proposed by the Global Programme on AIDS of the World Health Organization, for general use in collecting population-based data on HIV seroprevalence. It appears that in real populations, where there is likely to be 'pocketing' of infection, the proposed methodology will generally fail to provide estimates accurate to within 1% of the true population value. However, if the primary objective of a particular survey is to construct confidence intervals that include the true population HIV seroprevalence rate, then this survey method appears to be a reasonable choice. This study also suggests that selection of only one adult per household improves the precision of resulting estimates. However, since selection of only one adult per household would require that more households be visited, any gain in precision would need to be weighed against the likely increase in cost of household visits.

Acquired Immunodeficiency Syndrome↗
PubMed1991

The importance of assessing the fit of logistic regression models: a case study.

BACKGROUND: The logistic regression model is being used with increasing frequency in all areas of public health research. In the calendar year 1989, over 30% of the articles published in the American Journal of Public Health employed some form of logistic regression modeling. In spite of this increase, there has been no commensurate increase in the use of commonly available methods for assessing model adequacy. METHODS: We review the current status of the use of logistic regression modeling in the American Journal of Public Health. We present a brief overview of currently available and easily used methods for assessing the adequacy of a fitted logistic regression model. RESULTS: An example is used to demonstrate the methods as well as a few of the adverse consequences of failing to assess the fit of the model. One important adverse consequence illustrated in the example is the inclusion of variables in the model as a result of the influence of one subject. CONCLUSIONS: Failure to address model adequacy may lead to misleading or incorrect inferences. Recommendations are made for the use of methods for assessing model adequacy and for future editorial policy in regard to the review of articles using logistic regression.

Bias↗
PubMed1991

Evaluation of the EPI survey methodology for estimating relative risk.

Precision in estimation of relative risks using a standardized sampling method proposed by the WHO Global Programme on AIDS was evaluated using a Monte Carlo model simulating actual populations; the proposed survey design represents a modification of the methodology used by the WHO Expanded Programme on Immunization (EPI) to estimate immunization coverage among children. This study suggests that in actual populations the proposed survey strategy is a reasonable alternative to the use of simple random sampling (SRS) at the second stage of cluster sampling. Although varying such population characteristics as the seroprevalence rate, nonresponse rate, and rate of misclassification of exposure failed to demonstrate a clear advantage of one method over the other, the added cost and difficulty of implementing SRS under field conditions warrant further consideration of the EPI-like methodology for use in estimating relative risks.

Adult↗
PubMed1991

Lot quality assurance sampling: single- and double-sampling plans.

Lot quality assurance sampling (LQAS) was originally developed for industrial applications. This article discusses the extension of its application to a public health setting. When resources must be allocated to several communities based on whether or not each exceeds a target proportion of members with a characteristic, a sampling scenario arises which is different to the standard parameter estimation scenario. LQAS is an efficient procedure for sampling in this instance. Under certain conditions, double sampling may further enhance the efficiency of an LQAS plan. LQAS is discussed and illustrated by examples, and the theoretical foundations of single and double lot quality assurance sampling are presented. Examples of sample size and critical value tables are also presented.

HIV Seroprevalence↗
PubMed1990

Timing of intensive care unit admission in relation to ICU outcome.

This study assessed the relationship between admission time (from hospital admission to ICU admission) and mortality predicted by the Mortality Prediction Model (MPM), actual mortality, and resource use. All admissions, except elective surgery patients, to the general medical/surgical ICU of a tertiary care hospital during a 24-month period were studied (n = 1,889). Patients admitted to the ICU within 1 day of hospital admission had lower predicted and actual mortality, and used fewer resources than patients admitted later. Predicted mortality was higher than actual mortality for patients admitted to the ICU early and was lower than actual mortality for later ICU admissions. Transfers had higher predicted and actual mortality, and used more resources than nontransfer patients. Time from hospital admission to ICU admission can be a potentially useful variable in models of ICU outcome.

Adult↗
PubMed1990

Explaining variability of cost using a severity-of-illness measure for ICU patients.

Factors related to hospital resource use by intensive care unit (ICU) patients, including severity of illness at admission and intensity of therapy during the first 24 ICU hours were explored in this study. Analysis was based on 2,749 patients admitted to the general medical-surgical ICU at Baystate Medical Center, Springfield, Massachusetts, between February 1, 1983 and January 10, 1985. Resource use was indexed by hospital length of stay (LOS) adjusted for differences between ICU and other hospital days. Severity of illness was measured by the Mortality Prediction Model (MPM0), a validated predictor of outcome but not previously used to analyze resource consumption. Intensity of therapy was measured using the Therapeutic Intervention Scoring System (TISS). The 10% of patients with longest ICU stays were significantly different from the other 90% with respect to previous ICU use, MPM probability, and TISS score. Variability in resource use was analyzed using four diagnosis-related groups (DRGs) accounting for large numbers of ICU patients. The relationship between severity of illness and resource was nonlinear: as severity increased from low levels, resource use increased at a decreasing rate, reached a plateau, and eventually declined. Within each DRG, MPM0 explained a statistically significant percentage of the variability in resource use.

Costs and Cost Analysis↗
PubMed1989

Intensive care unit patient follow-up. Mortality, functional status, and return to work at six months.

Six months after hospital discharge, we followed up 1545 patients who had received care in the general medical-surgical intensive care unit (ICU) of a tertiary care hospital. Vital status could not be ascertained for 200 of these patients. Of the 1345 former ICU patients for whom a determination of vital status could be made, 1261 (94%) were alive and 84 (6%) had died. Of those known to be living, 887 (70%) responded to a questionnaire regarding employment, functional, and social status. A large proportion of survivors less than 40 years of age had returned to work. Younger patients admitted to the hospital for elective surgery reported as much compromise of physical and psychological activity as did older patients admitted for emergency reasons. Older survivors reported an increase of interaction with family members and a decrease of social interaction with those other than family.

Adult↗
PubMed1989

Pleural plaques.

Explore the source record for details and available documents.

Age Factors↗
PubMed1988

Sample size requirements for studies estimating odds ratios or relative risks.

This paper presents formulae for determining the number of subjects necessary, in either a case-control or a cohort study, to estimate the odds ratio or relative risk, respectively, to within a selected percentage (epsilon) of the true population value with some specified probability. This approach differs somewhat from previous comparable work that estimated the log odds ratio within a stated fixed distance rather than as a percentage of the actual odds ratio. Comparable development for relative risk has not previously appeared in the literature. These formulae provide guidelines for determination of study size that does not depend on hypothesis testing considerations.

Epidemiologic Methods↗
PubMed1988

Refining intensive care unit outcome prediction by using changing probabilities of mortality.

Estimating prognosis is potentially useful as a measure of ICU performance and as a guide for the clinical care of individual patients. In this study, mortality prediction models (MPMs) for patients in an adult general medical-surgical ICU were derived from data gathered at ICU admission and after 24 and 48 h of ICU care. A predictive model was developed which incorporated a sequence of probabilities collected over time in the ICU. The results of this study suggest that using serial observations may enhance substantially the usefulness of the MPM as a vehicle for helping families anticipate the patients' likely outcome.

Humans↗
PubMed1988

Prospective study of clinical bleeding in intensive care unit patients.

We investigated prospectively clinical bleeding in 1,328 consecutive patients admitted to a medical/surgical ICU over 1 yr. One hundred thirty-eight (10.4%) patients bled after ICU admission, and an additional 388 (29.2%) bled coincident with admission. The upper GI tract was the site of bleeding in 34.8% of patients whose bleeds commenced in the ICU, and accounted for 22% of total sites. Patients with clinical bleeding after ICU admission had a significantly (p less than .001) higher likelihood of death than those who did not bleed, and those with multiple bleeding sites had a higher mortality (54.9%) than those with single sites (31%) (p less than .006). Multiple logistic regression analyses revealed that risk ratios (RR) for bleeding after ICU admission were mechanical ventilation (RR = 1.82), nutritional failure (RR = 3.45), acute renal failure (RR = 3.36), antiulcer medication (RR = 3.36), and anticoagulants (RR = 4.19). No antibiotics could be specifically incriminated. This study defines the scope, characteristics, and importance of bleeding in ICU patients and establishes risk factors.

Aged↗
PubMed1988

The effect of temperature and hematocrit level of oxygenated cardioplegic solutions on myocardial preservation.

The ideal temperature and hematocrit level of blood cardioplegia has not been clearly established. This study was undertaken (a) to determine the optimal temperature of blood cardioplegia and (b) to study the effect of hematocrit levels in blood cardioplegia. A comparison of myocardial preservation was done among seven groups of animals on the basis of variations in hematocrit levels and temperature of oxygenated cardioplegic solution. The experimental protocol consisted of a 2-hour hypothermic cardioplegic arrest followed by 1 hour of normothermic reperfusion. Group 1 received oxygenated crystalloid cardioplegic solution at 10 degrees C. Groups 2 through 7 received oxygenated blood cardioplegic solution with the following hematocrit values and temperatures: (2) 10%, 10 degrees C; (3) 10%, 20 degrees C; (4) 10%, 30 degrees C; (5) 20%, 10 degrees C; (6) 20%, 20 degrees C; and (7) 20%, 30 degrees C. Parameters studied include coronary blood flow, myocardial oxygen extraction, myocardial oxygen consumption, and myocardial high-energy phosphate levels of adenosine triphosphate and creatine phosphate during control (prearrest), arrest, and reperfusion. Myocardial oxygen consumption at 30 degrees C during arrest was significantly higher than at 10 degrees C and 20 degrees C, which indicates continued aerobic metabolic activity at higher temperature. Myocardial oxygen consumption and the levels of adenosine triphosphate and creatine phosphate during reperfusion were similar in all seven groups. Myocardial oxygen extraction (a measure of metabolic function after ischemia) during initial reperfusion was significantly lower in the 30 degrees C blood group than in the 10 degrees C blood group at either hematocrit level and in the oxygenated crystalloid group, which suggests inferior preservation. The hematocrit level of blood cardioplegia did not affect adenosine triphosphate or myocardial oxygen consumption or extraction. It appears from this study that blood cardioplegia at 10 degrees C and oxygenated crystalloid cardioplegia at 10 degrees C are equally effective. Elevating blood cardioplegia temperature to 30 degrees C, however, reduces the ability of the solution to preserve metabolic function regardless of hematocrit level. Therefore, the level of hypothermia is important in blood cardioplegia, whereas hematocrit level has no detectable impact, and cold oxygenated crystalloid cardioplegia is as effective as hypothermic blood cardioplegia.

Adenosine Triphosphate↗
PubMed1987

Validation of the mortality prediction model for ICU patients.

We tested recently developed admission and 24-h models of hospital mortality on 1,997 consecutive admissions to a general medical/surgical ICU. This study population was independent of the group used to develop the models. The admission prediction model estimated each patient's probability of hospital mortality based on seven routinely collected admission variables. The 24-h model utilized seven variables routinely available at 24 h in the ICU. The admission model accurately described the mortality experience of the new cohort, while the 24-h model did not. Advantages of the admission model are that it is evaluable at the time of ICU admission, is independent of ICU treatment, and can be used to stratify patients by severity of illness, thereby making ICU comparisons possible. Its excellent goodness-of-fit, correct classification rate, sensitivity, and specificity suggest that this model is now ready for multihospital testing.

Aged↗
PubMed1987

A comparison of methods to predict mortality of intensive care unit patients.

This paper presents results of the first study explicitly designed to compare three methods for predicting hospital mortality of ICU patients: the Acute Physiology Score (APS), the Simplified Acute Physiology Score (SAPS), and the Mortality Prediction Model (MPM). With respect to sensitivity, specificity, and total correct classification rates, these methods performed comparably on a cohort of 1,997 consecutive ICU admissions. In these patients from a single hospital, the APS overestimated and the SAPS underestimated the probability of hospital mortality. The MPM probabilities most closely matched the observed outcomes. Each method holds considerable promise for assessing the severity of illness of critically ill patients. The MPM should be particularly useful for comparing ICU performance, since it is independent of ICU treatment and can be calculated at the time a patient is admitted.

Diagnosis-Related Groups↗
PubMed1987

Age-related development profiles of the antioxidative defense system and the peroxidative status of the pig heart.

The developmental profiles of the antioxidative defense system and the peroxidative status of the heart during growth and development were studied in pigs of three different age groups. A unique age-specific myocardial lipid peroxidation expressed in terms of malonaldehyde formation occurred after incubation of neonatal and adult pig heart homogenates in the absence of any added factors. Very little malonaldehyde release was noticed in the 0- to 2-day age group, while considerably higher activity was found in the 8- to 10-day-old animals. The 2-month-old pig heart again formed very little malonaldehyde. Myocardial injury from lipid peroxidation was highest in the 0- to 2-day age group, as evidenced by the release of oxidized glutathione, lactate dehydrogenase (LDH) and creatine kinase (CK) activities. Release of glutathione, LDH and CK decreased with age and was minimal in the adult group. The antioxidative enzymes, superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, increased during the first 10 days of neonatal growth and then levelled off. Glucose-6-phosphate dehydrogenase was present in appreciably lower amounts in adult hearts compared to neonatal hearts. Heart weight increased with aging, but myocardial water content decreased. Protein and DNA contents of hearts increased with age, such that the protein/DNA ratio almost doubled from the newborn to adult age. The results indicate that the newborn pig hearts are equipped with the antioxidative defense system, which undergoes significant development during the initial phase of neonatal growth and does not change appreciably thereafter. The results further suggest that the change in activity profile with aging is different for different enzymes, and the peroxidative status of the myocardium is not a function of these enzyme activities.

Aging↗
PubMed1987

Blood conservation for myocardial revascularization. Is it cost effective?

A total of 284 patients undergoing myocardial revascularization were prospectively studied to determine if the use of intraoperative autotransfusion or intraoperative autotransfusion plus postoperative reinfusion of shed mediastinal blood decreased transfusion requirements and the use of one or both techniques was cost effective. The Haemonetics Cell Saver System was used for intraoperative autotransfusion and the Sorenson Receptaseal autotransfusion system for postoperative reinfusion of shed mediastinal blood. During Phase 1, the Cell Saver System was used for 57 patients and 93 patients served as a control group. During Phase 2, the Cell Saver System plus the autotransfusion system were used in 43 patients and 91 patients were in the control group. Separate parallel analyses to compare the blood conservation groups to control groups were conducted for each phase of the study. The patient groups were comparable with regard to age, sex, preoperative red cell mass, preoperative hematocrit value, number of bypasses, and use of internal mammary grafts. Blood conservation techniques resulted in significant reductions in the use of bank blood. During Phase 1, Cell Saver System patients received an average of 2.8 units of packed cells versus 4.7 units for control patients. Transfusion was avoided entirely in 14% of Cell Saver System patients compared to 3% of control patients. During Phase 2, patients subjected to both the Cell Saver System and the autotransfusion system received an average of 1 unit of packed red cells versus 3 units for control patients. Transfusion was required in only 42% of patients subjected to both the Cell Saver System and the autotransfusion system compared to 85% of control patients. Multiple logistic regression analysis confirmed that the use of the Cell Saver System in Phase 1 and the Cell Saver System and autotransfusion system in Phase 2 were each independently predictive of decreased transfusion requirements. The total "blood-related costs" (including cost for all bank blood products plus Receptaseal and Cell Saver System equipment) was slightly lower for the blood conservation patients in both Phase 1 ($555.00 versus $615.00, no significant difference) and Phase 2 ($373.00 versus $426.00, no significant difference). Intraoperative use of the Cell Saver System is associated with substantial savings of bank blood, and the addition of postoperative reinfusion of shed mediastinal blood results in further bank blood savings. The use of blood conservation techniques is cost effective; that is, the costs incurred for the blood conservation equipment are more than offset by the resultant dollar savings for blood products.

Blood Transfusion, Autologous↗
PubMed1987

The mechanism of myocardial reperfusion injury in neonates.

Oxygen free radicals and phospholipid degradation have been implicated in the pathogenesis of ischemia and reperfusion injury. The present study examines the involvement of such mechanisms in myocardial reperfusion injury in neonatal hearts. The isolated neonatal pig hearts from two different age groups, 0 to 2 days old (newborn) and 7 to 9 days old (week-old), were subjected to 60 min of normothermic global ischemia followed by 60 min of reperfusion. Although myocardial ischemia reduced superoxide dismutase, catalase, and glutathione peroxidase activities in both age groups, superoxide dismutase and catalase activities remained significantly lower in the newborn pig heart during ischemia and reperfusion. Oxidized glutathione release from the neonatal pig hearts was at minimum levels before ischemia, but it increased 10-fold at the onset of reperfusion and was significantly higher in the newborn heart. This indicates that generation of oxygen free radicals was enhanced in the newborn compared with that in the week-old heart. The increase in phospholipase A2 activity and decrease in acyl CoA synthetase and lysophosphatidylcholine acyl transferase activities during ischemia and reperfusion were associated with comparable loss of membrane phospholipids and accumulation of lysophosphatidylcholine and free fatty acids in both age groups, except that oleic acid content was significantly higher in the newborn heart during reperfusion. Myocardial damage appears to be potentiated in the newborn heart during reperfusion, as evidenced by higher release of creatine kinase and a lower content of high-energy phosphates. These results indicate that oxygen free radicals may play a crucial role in the occurrence of reperfusion injury in immature hearts.

Animals↗