False positive finding

Ensure that the analytical methodology gives reliable results in terms of identity (absence of false-positive findings) and of absence (no false-negative findings) of the analyte(s). This requires processing of concurrent analytical quality control samples. 

A method proposed by Schweder and Spjotvoll (1982) is based on a plot of the cumulative distribution of observed p values. Farrar and Crump (1988) have published a statistical procedure designed not only to control the probability of false positive findings, but also to combine the probabilities of a carcinogenic effect across tumor sites, sexes, and species. 

Despite the high sensitivity of [ F]-FDG-PET false-positive findings—due to physiological processes such as brown fat, colonic and gynecologic activity, infectious and inflammatory processes and rebound thymic hyperplasia—pose a major challenge. 

It has surprised this reviewer that in the effort to lower the rate of false-positive findings in neonatal screening and in young infants there has not been much attention paid to measurement of 21-deoxycortisol, another key analyte overproduced in CAH. 

Smooth dissections (Lucas et al. 2000) or less impressive vessel lesions, especially in elongated vessels of the posterior circulation, are diagnostically problematic. In these cases, a DSA is sometimes necessary. False positive findings arise if vascular steps in secondary reconstructions of MR angiographic data sets are mistaken as pathologic wall lesions, which predominantly occur with insufficient spatial resolution. 

Whenever we investigate a situation where there is no real difference present, a is the risk that we will generate a false positive finding. With the usual 95 per cent CIs, a is 5 per cent. 

Unless special precautions are used, multiple testing will increase the risk of generating false positive findings beyond the level of 5 per cent that is normally tolerated. 

Cholinergic hypersensitivity can be tested by using pilocarpine in 0.0625%, 0.1%, 0.125%, or 0.25% solution (Table 22-5).The usefulness of the pilocarpine test in eliciting cholinergic hypersensitivity depends on the presence of a standardized concentration of dmg at the iris. Thus any clinical procedure that compromises the corneal epithelium, the use of wetting agents, or other factors that enhance corneal penetration may result in false-positive findings. 

In summary, interpretation of mean effect data arising from such studies is not trivial, and the potential for a variety of false-negative and false-positive findings is a reality. Given signihcant current uncertainty, further regulatory, clinical, and pharmacometric research should be conducted to deal with these issues. The FDA is actively working with sponsors, the pharmaceutical industry, and academia to best handle these issues. 

Differential expression analysis refers to finding genes that are expressed at different levels between two experimental conditions. Numerous methods have been applied to the identification of differentially expressed genes in microarray studies. The simplest, nonstatistical test method often used is the fold change method. In this method, the ratios between expression levels in two conditions are evaluated. Genes with a ratio higher than an arbitrary cutoff value are considered to be differentially expressed [26]. However, as a nonstatistical test, this approach offers no associated level of confidence. It also does not provide any control on the number of false-positive findings. 

Fig.9.1. Free-response receiver operating characteristic (ROC) curves for screen-film mammography (Square boxes, dotted line) and full-field digital mammography (dosed diamonds, solid line) based on rating scale of 0-100. Scale for a -axis is probability of false-positive finding occurring on two screen-...

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