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J R Landis

Publications and source records attributed to J R Landis.

At least 37 records · Page 2Linked to original sources
PubMed1997

Associations among cystoscopic and urodynamic findings for women enrolled in the Interstitial Cystitis Data Base (ICDB) Study.

OBJECTIVES: Interstitial cystitis is a symptom complex characterized by pelvic pain, urinary urgency, urinary frequency, and nocturia. Patients with these symptoms, at the 5 clinical centers participating in the National Interstitial Cystitis Data Base (ICDB) Study, have been evaluated with history and physical exams, questionnaires, and urodynamic studies. METHODS: Of the 388 female subjects entered in the study as of December 31, 1995, 150 women have undergone cystoscopy with hydrodistension. The data from the endoscopic procedures and the urodynamic studies were analyzed. The associations among cystoscopic and urodynamic findings were reviewed. RESULTS: Patient demographics of this subgroup show a predominance of Caucasians 139/150 (92.7%), with the average age being 43 (+/-13.2) years. Of the total, 17 patients (11.3%) had a Hunner's patch (HP). The prevalence by center varied from a low of 2/38 (5.3%) to a high of 3/9 (33.3%). Bloody effluent following hydrodistension was present in 113/150 (75.3%). Glomerulations appeared in varying degrees (mild, moderate, severe) in 91.3% of the 150 patients. There was a strong inverse relationship (P < 0.001) between bladder capacity under anesthesia and the presence of a HP (mean of 845 cc with HP absent versus a mean of 531 cc when present). The incidence of HP varied from 67.6% among women with a bladder capacity at hydrodistension of < 400 cc to 3.8% for those with a bladder capacity of at least 800 cc. The presence and increasing severity of glomerulations was positively associated (P < 0.003) with the presence of HP, ranging from 0/13 (0%) when glomerulations were not present to 6/31 (19.4%) when glomerulations were graded as severe. Of the patients with HP, 17/17 (100%) had glomerulations after hydrodistension. HP is more closely associated with the moderate to severe range of glomerulations (P < 0.01). Nearly half of the patients with HP or 8/17 (47.1%) had "moderate" glomerulations, while 6/17 (35.3%) had "severe" glomerulations. The volume at first sensation to void on urodynamics (mean 87 cc without HP versus 34.7 cc with HP) was highly inversely associated (P = 0.002) with the presence of HP, but not with any of the other cystoscopic findings. Of patients with HP, 94% had a volume at first sensation to void of < or = 50 cc where only 36% of patients without HP had a volume at first sensation to void of < or = 50 cc. The volume at maximum capacity on urodynamics was positively associated with the volume at hydrodistension (P < 0.001). CONCLUSIONS: Overall, patients with HP had lower bladder capacities, lower volumes at first sensation to void, and more severe glomerulations. Thus, the presence of HP would imply a more severe case of interstitial cystitis. Logically, a higher bladder capacity on cystometrogram is associated with a higher volume at the time of hydrodistension, and bloody effluent is associated with more severe glomerulations.

Adult↗
PubMed1997

Interaction fallacy.

We define interaction fallacy as the situation in which heterogeneity of odds ratios suggests an interaction that does actually not exist among the corresponding risk ratios. We provide a hypothetical example of interaction fallacy between the presence of the germ-line BRCA1 mutation, age at first live birth, and breast cancer risk based on data from the literature. More generally, we present a set of hypothetical conditions under which interaction fallacy may occur.

Adult↗
PubMed1996

Population-averaged and cluster-specific models for clustered ordinal response data.

We compare population-averaged and cluster-specific models for clustered ordinal data. We consider generalized estimating equations and constrained equations maximum likelihood estimation of population-averaged cumulative logit regression models, and mixed effects estimation of cluster-specific cumulative logit regression models. A previously reported relationship between population-averaged and cluster-specific parameters for the binary logistic link appears to hold for analogous parameters under the cumulative logit link. We address these issues in the context of data from two cross-over clinical trials.

Chi-Square Distribution↗
PubMed1996

A novel system for intracoronary beta-irradiation: description and dosimetric results.

PURPOSE: A dosimetric evaluation of a new device dedicated to intravascular irradiation, associating a beta source and a centering device, was carried out before initiation of a clinical pilot study. METHODS AND MATERIALS: A 29-mm-long 90Y coil, coated with titanium and fixed to the end of a thrust wire, was introduced into the inner lumen of purpose-built centering balloons of different diameters (2.5, 3, 3.5, and 4 mm). Dose homogeneity was evaluated by studying both axial and circumferential dose variations, based on readings from thermoluminescent dosimeters (TLDs) placed on the balloon surface. Axial homogeneity was determined by comparing the readout values of dosimeters located on peripheral balloon segments with those located on segments adjacent to the midpoint of the source. The centering ability of the device was studied by comparing measurements on opposing surfaces of the balloon. The dose attenuation by water and contrast medium was evaluated and compared with that in air. The balloon contamination was studied using a contamination counter. The total 90Y coil activity was measured by liquid scintillation to relate activity to surface dose. RESULTS: Activity-surface dose correlation showed that for a linear coil activity of 1 mCi/mm, the mean dose rate at the surface of a 2.5-mm balloon filled with contrast medium was 8.29 Gy/min. The doses at the surface of larger balloons (3, 3.5, and 4 mm) filled with contrast were 78%, 59%, and 47%, respectively, of the dose measured at the surface of the 2.5-mm balloon. The coefficient of variation (CV) in surface dose for 2.5-, 3-, 3.5-, and 4-mm centering devices filled with contrast medium were 9%, 8%, 9%, and 12%, respectively. There was no statistically significant difference between readouts from central and peripheral balloon segments or among rows of dosimeters facing each other. For a 2.5-mm balloon, compared with air the dose attenuation by water and contrast medium was similar (0.70 and 0.69, respectively), but a significant difference was seen between the readouts of water- and contrast-filled balloons when the diameter was larger than 3 mm (p < 0.001). No contamination was found in the balloon shaft after source retrieval. CONCLUSION: The dosimetric tests showed very good surface dose homogeneity, demonstrating satisfactory centering of the source within the centering balloons. The achievable dose rates will permit intravascular irradiation within a short time interval. The absence of residual balloon contamination after source retrieval meets the requirements for a sealed source used in a clinical setting.

Brachytherapy↗
PubMed1996

Identifying adverse events caused by medical care: degree of physician agreement in a retrospective chart review.

OBJECTIVE: To 1) assess the degree of agreement among physicians on the cause of previously flagged adverse outcomes and 2) relate the findings to systems of quality assurance and performance assessment and proposals for no-fault compensation for medical injuries. DESIGN: Observational study of 7533 pairs of "structured implicit" reviews (subjective opinions based on guidelines) of medical records done by 127 physicians working independently. SETTING: Random sample of 51 inpatient facilities in New York State. PATIENTS: Random sample of inpatient medical records from the selected facilities. MEASUREMENTS: 1) Number of agreed-upon adverse events compared with the number of cases of extreme disagreement and 2) internally and indirectly standardized rates at which physician reviewers found adverse events (injuries to patients caused at least in part by medical management). RESULTS: In 12.9% of cases (971 of 7533), the two physicians in a pair had extreme disagreement about the occurrence of an adverse event. These cases outnumbered those in which both reviewers found an adverse event (10%; n = 757). Agreement was highest for wound infections and lowest for adverse events attributed to failure to diagnose or lack of therapy. The amount of experience the physicians had in reviewing records tended to increase the level of agreement. Even after standardization to the results of the entire sample, individual physicians' rates of finding at least slight evidence of an adverse event varied widely (range, 9.9% to 43.7%) (P < 0.001). CONCLUSIONS: Structured implicit reviews produced disagreement on the causes of adverse patient outcomes. If systems of quality assurance, performance audits, or no-fault patient compensation are to succeed, methods for overcoming the common tendency toward disagreement among experts must be developed.

Humans↗
PubMed1995

Model-based estimation of population attributable risk under cross-sectional sampling.

The covariate-adjusted population attributable risk (PAR) measures the proportionate reduction in disease prevalence in the target population when the putative risk factor is removed, after adjusting for covariate effects. This paper extends the model-based approach developed for retrospective and cohort studies to the cross-sectional sampling design. An appropriate logit linear model is utilized to estimate the covariate-adjusted attributable risk. The asymptotic variance of this complex ratio estimate is obtained using Taylor series expansions which incorporate the sampling variation of the estimated model parameters and the appropriate estimates of risk factor prevalence. These methods are illustrated with cardiovascular disease risk factor data from the second National Health and Nutrition Examination Survey (NHANES II).

Adolescent↗
PubMed1995

Association models for periodontal disease progression: a comparison of methods for clustered binary data.

We investigate population-averaged (PA) and cluster-specific (CS) associations for clustered binary logistic regression in the context of a longitudinal clinical trial that investigated the association between tooth-specific visual elastase kit results and periodontal disease progression within 26 weeks of follow-up. We address estimation of population-averaged logistic regression models with generalized estimating equations (GEE), and conditional likelihood (CL) and mixed effects (ME) estimation of CS logistic regression models. Of particular interest is the impact of clusters that do not provide information for conditional likelihood methods (non-informative clusters) on inferences based upon the various methodologies. The empirical and analytical results indicate that CL methods yield smaller test statistics than ME methods when non-informative clusters exist, and that CL estimates are less efficient than ME estimates under certain conditions. Moreover, previously reported relationships between population-averaged and cluster-specific parameters appear to hold for the corresponding estimates in the presence of these clusters.

Cluster Analysis↗
PubMed1995

Comparing hospital mortality in adult patients with pneumonia. A case study of statistical methods in a managed care program.

OBJECTIVE: To compare and contrast a managed care program's analysis of differences in hospital mortality with results obtained by accepted statistical methods. DESIGN: A re-analysis of computerized discharge data using the same method used by a managed care program, and using conventional methods of categorical data analysis. One thousand computer simulations of a method for comparing hospitals by severity-adjusted mortality were done to determine the probability of falsely identifying hospitals as high-mortality outliers. SETTING: 22 acute care hospitals in central Pennsylvania. PATIENTS: All adult patients with pneumonia (n = 4587; diagnosis-related groups 089-090) less than 65 years of age who were discharged from the 22 hospitals in 1989, 1990, and 1991, excluding patients with the acquired immunodeficiency syndrome and transplant recipients. MEASUREMENTS: In-hospital mortality adjusted for age and severity of illness using MedisGroups admission severity group score. RESULTS: The hospital that had the highest mortality for adult pneumonia according to the managed care program's analysis did not, according to an appropriate analysis, differ significantly from other area hospitals (likelihood ratio test, P = 0.23). Random variation in this sample of patients with a low average mortality rate (3.5%) showed a 60% chance that 1 or more of the 22 hospitals would be falsely identified as a "high-mortality outlier" when simplistic statistical methods were used. CONCLUSION: Organizations seeking to compare the quality of hospitals and physicians through outcome data need to recognize that simplistic methods applicable to large samples fail when applied to the outcomes of typical patients, such as those admitted for pneumonia. Although these comparisons are much in demand, careful attention must be paid to their statistical methods to ensure validity and fairness.

Adolescent↗
PubMed1995

Empirical evaluation of the influence of control selection schemes on relative risk estimation: the Welsh nickel workers study.

OBJECTIVE: To perform an empirical evaluation of the theory that relative incidence rate (RIR) and relative risk (RR) can be directly estimated from case-control studies that have different sampling schemes of controls. METHODS: With data from the South Wales nickel refinery workers (SWNRW) study, a nested case-control study of the relation of nickel exposure to respiratory cancers, was conducted within each of four fixed subcohorts that differed for stability of exposure, incidence rates and RIR. Odds ratios (ORs) and confidence intervals (CIs) were estimated either with all available controls or with randomly sampled subsets of controls. RESULTS: Respiratory cancers were not rare as risk of nasal and lung cancer in workers unexposed to nickel varied from 15% to 26% over the full risk period. The RIR was adequately estimated by the OR when controls were identified concurrently to case occurrence throughout the risk period. The RR was well approximated with the OR when controls were a sample of the study base. CONCLUSIONS: These results add empirical support to the theory that the RIR or the RR can be validly estimated in case-control studies. Overall, this theory is relatively tolerant of large departures from the stability assumptions of exposure and of incidence.

Case-Control Studies↗
PubMed1994

Secular trends in blood pressure among adult blacks and whites aged 18-34 years in two body mass index strata, United States, 1960-1980.

Secular trends in blood pressure among young adults reflect the proportion of the population at risk of developing hypertension and may be markers of progress in primary prevention. National health examination data from three successive surveys were analyzed to assess blood pressure trends for adult blacks and whites aged 18-34 years in two body mass index (BMI; weight (kg)/height (m)2) strata (< 25 or > or = 25). Blood pressure was categorized into a four-point ordinal scale using the weighted, within-sex 50th, 75th, and 90th percentiles for 18- to 24-year-old adults in the 1960-1962 survey. The effects were analyzed with cumulative logit models with alpha = 0.01. The systolic blood pressure decreased moderately for 25- to 34-year-old males and for females except those aged 25-34 years with a BMI of > or = 25. Diastolic blood pressure increased among males with a BMI of > or = 25 and among white males with a BMI of < 25, but did not show a significant overall trend among females. A BMI of > or = 25 was associated with substantially higher blood pressure in each survey, except for one age-sex-race subgroup. Racial differences within BMI were less consistent than the differences across BMI strata. In summary, the situation with respect to hypertension among females may have improved during this time period but for males may have worsened with respect to diastolic blood pressure. Data for both sexes support a need for population-wide obesity prevention to reduce the incidence of hypertension.

Adolescent↗
PubMed1994

[Nutritional balance of the diet of the adult residents of Geneva].

Diet of the Swiss population has probably changed over the last 10 years, but these changes have not been recorded yet by nutritional studies. In the present study, 3 registered dieticians interviewed over the telephone 626 adults, resident of Canton Geneva, using a 24 hour recall. Interviews were performed during the 7 days of the week. Participants were randomly selected according to their age, sex and nationality. Participation was 80%. The following caloric (C) and nutritional intakes in proteins (P), lipids (L), carbohydrates (CH) and alcohol (A) were recorded: In non Swiss men: C = 2464 kcal/j., P = 16.2%, L = 32.4%, CH = 44.4%, A = 7.0%; in Swiss men: C = 2752 kcal/j., P = 15.3%, L = 34.0%, CH = 43.5%, A = 7.1%; in non Swiss women: C = 1897 kcal/j., P = 16.4%, L = 35.1%, CH = 46.5%, A = 2.4%; in Swiss women: C = 1865 kcal/j., P = 15.0%, L = 35.3%, CH = 46.0%, A = 3.2%. Total caloric intake and iron intake decreased with age. Older women ate less calcium than younger. In summary, the most important determinants of diet are age and sex. Proportion of lipids is relatively low in both men and women. Small differences related to nationality were observed in men.

Adult↗
PubMed1994

Longitudinal evaluation of elastase as a marker for the progression of periodontitis.

To determine whether elastase levels in gingival crevicular fluid (GCF) could serve as a marker for the progression of periodontitis, we monitored GCF elastase and periodontal status in selected sites in 32 periodontally healthy volunteers and 31 periodontitis patients at intervals over a 6-month period. Clinical measurements included plaque index, gingival index, bleeding on probing, suppuration, probing depth, clinical attachment level, and relative attachment level measured with an automated disk probe. GCF elastase, detected by reaction with a fluorescent substrate, was assessed visually against fluorescence standards and quantitatively with a fluorometer. Bone loss was detected by subtraction radiography of standardized vertical bite-wing radiographs at baseline and 6 months. Mean visual elastase scores (VES) and quantitative elastase measurements were significantly higher (P < 0.001) in sites from periodontitis patients than in sites from healthy volunteers. When bone loss was used as the criterion for disease progression, significantly higher (P < 0.001) visual and quantitative GCF elastase levels were found at progressing sites than in nonprogressing sites in the periodontitis patients. The odds ratios (OR) for the event of developing bone loss with positive 4-minute and 8-minute VES tests were 4.2 (P < 0.001) and 7.4 (P < 0.001), respectively. When corrected for the tendency of progressing sites to be clustered within a subpopulation of patients, the OR for developing bone loss with the 4-minute and 8-minute VES tests were 3.1 (P < 0.007) and 4.9 (P < 0.001), respectively. These data indicate that sites with high levels of elastase are at significantly greater risk for progressive bone loss as assessed by digital subtraction radiography.

Adult↗
PubMed1993

Calcium supplementation and bone mineral density in adolescent girls.

OBJECTIVE: To evaluate the effect of calcium supplementation on bone acquisition in adolescent white girls. DESIGN: A randomized, double-blind, placebo-controlled trial of the effect of 18 months of calcium supplementation on bone density and bone mass. SUBJECTS: Ninety-four girls with a mean age of 11.9 + 0.5 years at study entry. SETTING: University hospital in a small town. INTERVENTIONS: Calcium supplementation, 500 mg/d calcium as calcium citrate malate; controls received placebo pills. MAIN OUTCOME MEASURES: Bone mineral density and bone mineral content of the lumbar spine and total body were measured by dual-energy x-ray absorptiometry and calcium excretion from 24-hour urine specimens. RESULTS: Calcium intake from dietary sources averaged 960 mg/d for the entire study group. The supplemented group received, on average, an additional 354 mg/d of calcium. The supplemented group compared with the placebo group had greater increases of lumbar spine bone density (18.7% vs 15.8%; P = .03), lumbar spine bone mineral content (39.4% vs 34.7%; P = .06), total body bone mineral density (9.6% vs 8.3%; P = .05), and 24-hour urinary calcium excretion (90.4 vs 72.9 mg/d; P = .02), respectively. CONCLUSIONS: Increasing daily calcium intake from 80% of the recommended daily allowance to 110% via supplementation with calcium citrate malate resulted in significant increases in total body and spinal bone density in adolescent girls. The increase of 24 g of bone gain per year among the supplemented group translates to an additional 1.3% skeletal mass per year during adolescent growth, which may provide protection against future osteoporotic fracture.

Absorptiometry, Photon↗
PubMed1993

Relationship between malpractice claims and cesarean delivery.

OBJECTIVE: To investigate whether an association exists between the probability of a cesarean delivery and the level of malpractice claims risk faced by hospitals and physicians. DESIGN: Survey of computerized discharge data linked with physician and hospital malpractice claims records based on stratified, random sample of hospitals. SETTING: Acute care hospitals in New York State in 1984. POPULATION: All deliveries (60 490) at 31 hospitals. RESULTS: After controlling for the clinical risk of a cesarean delivery, patient socioeconomic status, and physician and hospital characteristics, cesarean delivery was positively associated with physician malpractice premiums (odds ratio [OR], 3.00; 95% confidence interval [CI], 2.13 to 4.24 for the difference between upstate and New York City levels), with the number of physician claims opened per 100 physicians at the hospital level (OR, 1.15; 95% CI, 1.02 to 1.30 for a 1-SD change), and with the number of hospital claims opened per 1000 discharges (OR, 1.26; 95% CI, 1.10 to 1.43 for a 1-SD change). Measures of physician-perceived risk of suit also showed a significant association with cesarean delivery (OR, 1.96; 95% CI, 1.53 to 2.52, upstate vs New York City). Within hospitals, there was no significant association (OR, 1.15; P = .126) between the odds of cesarean delivery and the claims history (none vs one or more) of an individual physician. CONCLUSION: Results support previous speculations of a positive association between malpractice claims risk and the rate of cesarean delivery.

Cesarean Section↗
PubMed1993

The analysis of longitudinal polytomous data: generalized estimating equations and connections with weighted least squares.

In recent years, methods have been developed for modelling repeated observations of a categorical response obtained over time on the same individual. Although situations in which the repeated response is binary or Poisson have been studied extensively, relatively little attention has been given to polytomous categorical response variable. In this paper, we extend the estimating equations initially developed for clustered discrete data by Liang and Zeger (1986, Biometrika 73, 13-22), and subsequently extended by Prentice (1988, Biometrics 44, 1033-1048), to polytomous response variables. Under certain assumptions, we illustrate that these estimating equations simplify to the weighted least squares (WLS) equations formalized by Koch et al. (1977, Biometrics 33, 133-158). This connection provides a formal framework for obtaining iterated weighted least squares model parameter estimates. Cumulative logit models are developed and applied to a representative longitudinal data set. Simulation results comparing WLS, an iterative form of WLS, and independence estimating equations using a robust estimate of the variance are presented.

Analysis of Variance↗
PubMed1992

31P-NMR evaluation of postischemia renal ATP and pH levels after ATP-MgCl2 treatment in rabbits.

Phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopy was used to measure adenosine triphosphate (ATP) concentration and pH in vivo in rabbits subjected to a 40-minute period of unilateral renal ischemia to determine the effect of infusing ATP-magnesium chloride (MgCl2, 100 mumol/kg) versus saline at the initiation of reperfusion. Data were compared initially by analysis of variance and then analyzed further using a general linear model with covariate adjustment. ATP-MgCl2-treated animals did not have higher ATP levels during recovery but did have significantly higher renal blood flow (p less than 0.05), a significantly decreased rate of recovery from acidosis (p less than 0.05), and significantly higher urinary output (p less than 0.01) than saline-treated animals during the recovery period. Therefore, treatment with ATP-MgCl2 improves postischemic functional parameters in this model of moderate injury without functioning as a direct source of ATP or its precursors. These data add support to the emerging concept that intracellular acidosis protects cells from reperfusion injury.

Adenosine Triphosphate↗