Showing papers on "False positive paradox published in 1969"

Quantitative assessment of bacterial contamination of open wounds by a slide technique

Abstract: The use of biopsy material for a smear preparation to determine the presence of bacteria in wounds is described. 97.4% of all smears observed correlated with their respective bacteriological counts. Of 72 slides corresponding to those plates having a count greater than 105,66 (91.7%) showed bacteria. No false positives were demonstrated, but 6 of 72 smears were falsely negative where counts were just borderline at 106, giving an 8.3% false negative result. These results are considered to be significant (P less than 0·01). With the aid of this technique the use of culture material can be reduced and successful wound closure can be achieved.

Some Problems in the Determination of the False Positive and False Negative Rates of Tuberculin Tests1

Abstract: The estimation of the rates of false positive and negative reactions to the tuberculin tine test was considered when the true sensitivity of patients to tuberculin is unknown and must be estimated from the Mantoux test. It was demonstrated that correct estimates of the error rates of the tine test depend directly and critically on the opposite error rate of the Mantoux test. The exact relationship was derived, and its practical importance was shown to depend on the true prevalence of tuberculosis in the population investigated.

Quantum efficiency and false positive rate.

Abstract: 1. This paper presents an analysis of the efficiency of performance at the absolute threshold of human vision. The data are from the same series as the previous papers (Hallett, 1969b, c) and consist of frequency-of-seeing curves, thresholds, false positive rates and equivalent background measurements, accumulated as small samples over a number of days. 2. Quantum efficiency is defined here as the ratio of the thresholds of an ideal and a real detector performing the same task with the same sampling error. This avoids the problem as to whether the frequency-of-seeing curve of the real detector is exactly a Poisson sum or not. 3. The long-term quantum efficiency can be low (about 0·04) as a result of drifts in the mean threshold. 4. The average short-term quantum efficiency is in the region of 0·1, which is roughly the physiological limit set by Rushton's (1956b) measurements of rhodopsin density in the living rods. If this is correct, then the absorption of a quantum, and not the bleaching of a rhodopsin molecule, is sufficient for the generation of a neural event. 5. Application of a simple signal/noise theory to the data gives solutions close to those suggested by Barlow (1956) and shows that false positives almost invariably arise from errors subsequent to the signal/noise decision process.