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Biomedical subjects

G C Critchfield

Publications and source records attributed to G C Critchfield.

9 recordsLinked to original sources
PubMed1990

Parental perceptions of genetic risk: correlation with choice of prenatal diagnostic procedures.

Determinants of patients' decisions to have prenatal diagnosis, and by which test (amniocentesis or chorionic villus sampling), is not well understood. We have administered questionnaires to couples referred for genetic counseling and procedures for advanced maternal age and determined patients' responses, decisions, and attributable determinants of their choice. Differences in perception of risks between partners, and choice of procedure, correlated with socioeconomic, educational status and age.

Adult↗
PubMed1989

A confidence profile analysis of the results of femoropopliteal percutaneous transluminal angioplasty in the treatment of lower-extremity ischemia.

The many reports on the use of percutaneous transluminal angioplasty (PTA) for treating lower-extremity ischemia were analyzed to determine the outcomes of femoropopliteal PTA used in patients with intermittent claudication (IC) and with more severe limb-threatening ischemia ("salvage"). The Confidence Profile Method was used to interpret and adjust the evidence from 12 selected clinical reports, and to combine the data into single best estimates of the outcomes that were considered important for decision making. The following combined estimates were obtained: The early success rate was 89% +/- 2.5% after PTA for IC, compared with 77% +/- 4% after PTA for salvage. The largest decline in patency occurred during the first 6 to 12 months. After 2 years there was little further attrition. Three-year patency was 62% +/- 9% for IC and 43% +/- 7% for salvage. The risk of procedure-related mortality and limb loss was low, estimated at 0.5% and 1%, respectively. The risk of serious complications requiring surgical repair was about 2.5%. The Confidence Profile Method is a novel way of obtaining this information from the imperfect clinical literature. The method incorporates subjective judgments and assumptions and gives quantitative and visual representations of both the magnitude of the estimated outcome and the uncertainty associated with it. The results are as strong as the assumptions incorporated in them are valid. The estimates derived in this study can be used for any decision on the use of PTA in the femoropopliteal segment.

Angioplasty, Balloon↗
PubMed1986

Probabilistic sensitivity analysis methods for general decision models.

Probabilistic sensitivity analysis has previously been described for the special case of dichotomous decision trees. We now generalize these techniques for a wider range of decision problems. These methods of sensitivity analysis allow the analyst to evaluate the impact of the multivariate uncertainty in the data used in the decision model and to gain insight into the probabilistic contribution of each of the variables to the decision outcome. The techniques are illustrated using Monte Carlo simulation on a trichotomous decision tree. Application of these powerful tools permits the decision analyst to investigate the structure and limitations of more complex decision problems with inherent uncertainties in the data upon which the decisions are based. Probabilistic sensitivity measures can provide guidance into the allocation of resources to resolve uncertainty about critical components of medical decisions.

Decision Theory↗
PubMed1985

Automatic prediction of platelet utilization by time series analysis in a large tertiary care hospital.

The authors investigated the potential of various time series models to aid in the prediction of platelet utilization patterns at the authors' institution. During a seven-week feasibility study, prediction accuracy of time series models was slightly inferior to that of an experienced platelet transfusion coordinator. The models that adjusted for day-of-the-week variability were superior to simpler models in a prospective evaluation over a three-month period. Conversion to a time series model for platelet utilization prediction has resulted in significant savings in personnel costs for management of platelet concentrate inventory in the blood bank. Outdate rates have been lower than those achieved by the platelet transfusion coordinator, with no sacrifice in availability occurring during the evaluation period.

Blood Banks↗
PubMed1985

Improved reference-interval estimation.

We used two standard methods (the common percentile and the log-power gaussian transformation) and two novel methods (weighted percentile and smoothed spline interpolation) to estimate the 2.5th and 97.5th percentiles of 1000 sets of data from eight diverse distributional forms, generated by Monte Carlo simulation. For each distributional form we derived an estimate of optimal performance. Although none of the four proposed methods closely approximated the optimal performance bound, the spline interpolation method and the weighted percentile method were superior to the two standard methods in accurately estimating percentiles.

Humans↗
PubMedDate not supplied

Nonparametric assessment of toxicologic assay linearity by bootstrap analysis.

An important aspect in the evaluation of toxicologic assay methodology is the assessment of calibration. This paper presents a new approach for validating calibration using bootstrap analysis. The technique is illustrated with a quantitative assay for benzoylecgonine in urine by gas chromatography/mass spectrometry (GC/MS). Because the bootstrap analysis does not rely on parametric assumptions regarding the distribution of errors about the regression line, it can be applied to situations where the parametric distribution of response errors about the regression line is unknown. This application of bootstrap methodology yields a probabilistic measure of confidence on the linearity of the calibration curve.

Calibration↗
PubMedDate not supplied

Probabilistic analysis of decision trees using Monte Carlo simulation.

The authors describe methods for modeling uncertainty in the specification of decision tree probabilities and utilities using Monte Carlo simulation techniques. Exact confidence levels based upon the underlying probabilistic structure are provided. Probabilistic measures of sensitivity are derived in terms of classical information theory. These measures identify which variables are probabilistically important components of the decision. These techniques are illustrated in terms of the clinical problem of anticoagulation versus observation in the setting of deep vein thrombosis during the first trimester of pregnancy. These methods provide the decision analyst with powerful yet simple tools which give quantitative insight into the structure and inherent limitations of decision models arising from specification uncertainty. The techniques may be applied to complex decision models.

Adult↗
PubMedDate not supplied

Probabilistic analysis of decision trees using symbolic algebra.

Uncertainty in medical decision making techniques occurs in the specification of both decision tree probabilities and utilities. Using a computer-based algebraic approach, methods for modeling this uncertainty have been formulated. This analytic procedure allows an exact calculation of the statistical variance at the final decision node using automated symbolic manipulation. Confidence and conditional confidence levels for the preferred decision are derived from gaussian theory, and the mutual information index that identifies probabilistically important tree variables is provided. The computer-based algebraic method is illustrated for a problem previously analyzed by Monte Carlo simulation. This methodology provides the decision analyst with a procedure to evaluate the outcome of specification uncertainty, in many decision problems, without resorting to Monte Carlo analysis.

Adult↗