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PubMed2005

Calculating control variables with age at onset data to adjust for conditions prior to exposure.

BACKGROUND: When assessing the association between a factor X and a subsequent outcome Y in observational studies, the question that arises is what are the variables to adjust for to reduce bias due to confounding for causal inference on the effect of X on Y. Disregarding such factors is often a source of overestimation because these variables may affect both X and Y. On the other hand, adjustment for such variables can also be a source of underestimation because such variables may be the causal consequence of X and part of the mechanism that leads from X to Y. METHODS: In this paper, we present a simple method to compute control variables in the presence of age at onset data on both X and a set of other variables. Using these age at onset data, control variables are computed that adjust only for conditions that occur prior to X. This strategy can be used in prospective as well as in survival analysis. Our method is motivated by an argument based on the counterfactual model of a causal effect. RESULTS: The procedure is exemplified by examining of the relation between panic attack and the subsequent incidence of MDD. CONCLUSIONS: The results reveal that the adjustment for all other variables, irrespective of their temporal relation to X, can yield a false negative result (despite unconsidered confounders and other sources of bias).

Adolescent↗
PubMed1986

Coronary heart disease mortality and alcohol consumption in Framingham.

The relationship between ethanol consumption and coronary heart disease was examined in the original Framingham Heart Study cohort (1948) with a 24-year follow-up from exam 2 (2,106 males and 2,639 females). Ethanol consumption shows a strong U-shaped relationship with coronary heart disease mortality for male nonsmokers and heavy smokers both in the raw age-adjusted data and in the Cox regression analyses, where ethanol consumption is modeled quadratically. No ethanol effects were found for female nonsmokers. The age-adjusted data suggest a U-shape curve for female smokers, although this was not confirmed by the Cox analysis. Separate analyses relating alcohol consumption to mortality from all causes showed similar effects except that the reduction in mortality for males was much less. For male coronary heart disease mortality, ethanol consumption was subdivided into beer, wine, and spirits consumption. These beverages were also modeled quadratically in the Cox analyses, and all showed strong U-shaped curves for both nonsmokers and heavy smokers. In nonsmokers, beer and wine show greater reductions in coronary heart disease mortality than spirits.

Adult↗
PubMed1997

All-payer severity-adjusted diagnosis-related groups: a uniform method to severity-adjust discharge data.

Measuring severity of illness within diagnosis-related groups (DRGs) has become increasingly important because of the growing need to compare outcomes across providers. In response to these needs, the Health Care Financing Administration (HCFA) has developed a DRG-based severity system as a refinement to its current Medicare DRG structure. As a result of this recent HCFA research, all-payer severity-adjusted DRGs (APS-DRGs) have been developed to provide a uniform approach for severity classification that is also applicable to the all-payer population.

Centers for Medicare and Medicaid Services, U.S.↗
PubMed1993

Smoothed nonparametric back-projection of AIDS incidence data with adjustment for therapy.

Back-projection is a major tool for assessing the extent of the HIV epidemic. Its application relies on a model for the incubation period of AIDS into which the administration and effect of therapy has been incorporated. We propose a compartmental model with proportional transition rates to describe variation and changes in the duration of the incubation period. The model is easily related to available data and offers fast computation. Its detailed and direct reflection of the administration and effect of therapy makes it relatively easy to ensure that therapy has been accommodated to an appropriate extent. The effect of therapy on back-projection estimates of the HIV epidemic curve is demonstrated with an application to Australian AIDS incidence data.

Acquired Immunodeficiency Syndrome↗
PubMed2003

Using lowess to remove systematic trends over time in predictor variables prior to logistic regression with quantile categories.

In case-control studies one may employ logistic regression to model the relationship between binary responses and continuous predictor variables that have been categorized by the empirical quartiles of the controls. Sometimes, however, systematic trends over time (or drifts) contaminate the laboratory measurements of predictor variables. In this paper we consider the use of locally weighted robust regression (lowess) to estimate and remove these systematic trends when the trends for the cases and controls have a common shape. One can then use the lowess adjusted data in the desired logistic regression model. We illustrate these methods with a case-control study that was designed to assess the risk of oesophageal cancer as a function of the quartile categories of sphinganine levels in the blood serum. Upon examination of the data, it was discovered that the sphinganine laboratory measurements were contaminated by a systematic trend, the magnitude of which depended only on the day of analysis. This trend needed to be removed before performing further analyses of the data. In addition, we present simulations to examine the use of lowess methods to estimate and remove various shapes of trends from contaminated predictor data before constructing logistic regression models with quartile categories. We found that using the trend-contaminated data tends to give attenuated parameter estimates and hence lower significance and power levels than using the uncontaminated data. Conversely, using appropriate lowess methods to adjust the data tends to give nearly unbiased parameter estimates, near nominal significance levels, and improved power.

Adult↗
PubMed1998

High ideals & perverse consequences: risk adjustments, encounter data & Medicare+Choice.

Why should you take on the risks and complications of developing a PSO? Is it worth it? Will it mean assuming undue risk? The answer to this question gets complicated. This article will introduce more uncertainties than you had before. But, you need to have your eyes wide open. It's not just a question of your capability as a health system or a medical group. It's a question of HCFA's ability to administer the program. Even without knowing the capabilities of HCFA, most organizations would say that they don't trust the government to follow through with any program. In this article by Bruce Fried, we get a rare look at the inner thoughts and gyrations of government, as they attempt to risk-adjust Medicare payments to PSOs and HMOs. In ordinary language, that means, if you happen to have a very sick population of seniors, you will be paid more to take care of them. But, read this and weep.

Aged↗
PubMed1994

A single-dose comparison of the bioavailability of aluminium from two formulations of sucralphate in normal volunteers.

The oral bioavailability of aluminium was compared after administration of 1 g sucralphate as either a tablet or a suspension (1 g/5 ml) in a crossover study in 16 healthy volunteers. Aluminium levels were detectable in all subjects pre-dose (21.4 +/- 8.8 micrograms l-1 before tablet; 21.4 +/- 7.4 micrograms l-1 before suspension) and there was a measurable increase in the plasma concentrations of aluminium in all subjects after administration of the suspension, and in 14 of the subjects after administration of the tablet formulation, with Cmax reached within the first 8 h in most subjects. Plasma levels were still elevated 72 h after dosing. The variability in plasma levels of aluminium was significantly higher after administration of the suspension (CV 39-53%) than after administration of the tablet (CV 29-44%), reflecting greater absorption of aluminium from the suspension formulation in three subjects. Similarly, the variance of the Cmax, AUC(0-72 h), and AUC(0-infinity) (for both the raw data and the baseline adjusted data) were all higher for the suspension than for the tablet. A point estimate of the difference of the pharmacokinetic parameters (determined from the median of the arithmetic Walsh averages) indicated little or no difference in Cmax, Tmax, or AUC(0-infinity) in the two formulations. In summary, the performance of the suspension formulation of sucralphate is more variable than the tablet formulation in vivo and some patients may therefore have higher circulating levels of aluminium on therapy with the suspension formulation.

Administration, Oral↗
PubMed1983

A comparison of methods for measuring event-related potentials.

Visual event-related potentials (ERPs) were recorded from 21 hyperactive children under 2 attention conditions and 4 doses of stimulant drug (methylphenidate). This data base was used to evaluate several methods of EP component measurement. These methods were (1) conventional visual peak and trough selection; (2) automatic feature extraction based on peaks; (3) automatic features extraction based on segments; (4) gross amplitude measures; (5) principal components analysis on normalized data and latency-adjusted data. No one method emerged as the best overall. Rather it is the case that different methods are best suited to different purposes, and criteria for choosing methods are outlined.

Brain↗
PubMed2005

Age-adjusted baseline data for women with hallux valgus undergoing corrective surgery.

BACKGROUND: Functional and health-related quality-of-life data on a population of patients with hallux valgus are lacking. Similarly, the correlation of the severity of the deformity with these measures is unknown. METHODS: Two hundred and eighty-five women with an average age of forty-nine years who were scheduled for bunion surgery were enrolled in the study. The patients completed a baseline American Academy of Orthopaedic Surgeons (AAOS) foot and ankle outcomes questionnaire, which includes the Short Form-36 (SF-36) and a specific lower-extremity section on the foot and ankle. Preoperative radiographic data with regard to the hallux valgus angle and the intermetatarsal angle were stratified into groups according to the severity of the deformity (mild, moderate, or severe). The data were then stratified into age-groups consistent with those reported for the SF-36, and the results were compared with the SF-36 scores for the general population. The global foot and ankle score and the shoe comfort score were compared with general population scores that were published previously. The severity of the preoperative deformity was correlated with the baseline scores. RESULTS: General health scores were noted to be relatively stable throughout the age-groups for patients with bunions, with the older groups demonstrating better scores than the general population. Bodily pain scores were consistently worse for patients with a bunion through all age-groups compared with the general population. The average global foot and ankle score and the shoe comfort score were significantly lower (p < 0.001 for both) for the patients with a bunion than for the general population. The severity of the preoperative deformity did not correlate with any of the outcome scores. CONCLUSIONS: The bodily pain score from the SF-36 appears to be a sensitive measure of problems experienced by patients undergoing bunion surgery. Surprisingly, the severity of the deformity as measured radiographically did not correlate with any of the fifteen scores measured. These data may serve as a baseline for clinical hallux valgus studies with use of the SF-36 or the AAOS outcomes questionnaire.

Age Factors↗
PubMed2006

[Optimization of basic adjustable data-acquisition parameters for continuous three-dimensional whole-body FDG-PET].

UNLABELLED: The SET-3000 G/X (Shimadzu Corp., Kyoto, Japan) has a large aperture and functions as a three-dimensional (3D) dedicated PET scanner. However, the large number of line of responses in the SET-3000 G/X scanner creates a large volume of sinogram data and prolongs reconstruction time in iterative reconstruction. The purpose of this study was to optimize basic acquisition parameters (maximum ring difference and span) for sensitivity and spatial resolution for 3D whole-body (18)F-FDG PET. METHODS: Detector rings and image planes numbered 50 and 99, respectively. In sensitivity measurement, the maximum ring difference (MRD) was changed from 1 to 49. In the measurement of spatial resolution, the span was changed from 3 to 21. For sensitivity and spatial resolution measurements, the standard protocols defined by the Japan Radioisotope Association (JRIA) 1994 and the National Electrical Manufacturers Association (NEMA) NU 2-2001 were used. We also evaluated the corresponding image noise by placing identical ROI on the reconstructed images. RESULTS: The total sensitivity of MRD=49 was 85.7 cps/Bq/ml in a uniform phantom (15 cm diameter, 30 cm tall cylinder) filled with (18)F. This was approximately two times higher than MRD=13. The image noise in the center of the axial FOV decreased with increasing MRD. Spatial resolution was slightly decreased as MRD increased, but axial resolution deteriorated with a span of more than 11. CONCLUSION: Optimum basic data-acquisition parameters for whole-body (18)F-FDG PET were MRD 49 to obtain maximum sensitivity and span 9 to avoid decreasing spatial resolution. Additionally, it was concluded that the basic data-acquisition parameters should be carefully selected for 3D whole-body (18)F-FDG PET in order to maximize the efficiency of PET measurement.

Electronic Data Processing↗
PubMed1990

The use of a severity-adjusted patient data base to establish standards for quality and cost-efficient medical practice.

In this article, the author describes the Acuity Index Method, a system that can be used to document levels of clinical quality and cost efficiency among physicians. This documentation can be used by physicians and health care institutions to analyze and enhance the quality of medical care they render and to demonstrate how quality medical care can be more cost-effective than "discount" medicine, with the patient being the ultimate beneficiary.

Algorithms↗
PubMedDate not supplied

Smoothed breastfeeding durations and waiting time to conception.

Breastfeeding beyond the resumption of mother's menstruation plays a significant role in the proximate determinants of fertility. Breastfeeding and postpartum amenorrhoea data collected from retrospective surveys usually exhibit digit preferences. Here, these heaping errors were smoothed by B-spline and used in multivariate models of risk of conception to investigate the contraceptive effect of breastfeeding. The data used come from a 1987 Indian survey. Results show that lactation, after mother's menses resume, reduces the risk of conception. Heaping in breastfeeding data attenuates this relationship. When adjustment is made, breastfeeding reduced the rate of conception by 47 per cent; the reduction, with adjusted data, was 63 per cent.

Adult↗