True-negative result

Fig. 26.1 Relative frequency distribution curves obtained during field evaluation of a competitive ELISA for drug residues the area represented by (A) contains the true-positive results (D) true-negative results (B) false-positive results (C) false-negative results.

Data should be presented showing the number or percentage of true negative results obtained by testing samples from animals that have not been exposed to the drug or chemical. As in the determination of tests sensitivity, this evaluation may need to be performed in a field environment. However, unlike sensitivity, the determination of the negative rate in the estimation of specificity does not require a separate confirmatory analysis. 

FP = False Positive Results TN = True Negative Results... 

The pumped-discharge case is generally more difficult to solve because of the uncertainty in deahng with negative numerical results. As a final answer, a negative value could indicate that the pump has completely emptied the tank however, as an intermediate value, it could mean that it is not a true solution. A simple check is to try a different initial estimate and see if the intermediate negative results disappear. 

The ability to identify and quantify cyanobacterial toxins in animal and human clinical material following (suspected) intoxications or illnesses associated with contact with toxic cyanobacteria is an increasing requirement. The recoveries of anatoxin-a from animal stomach material and of microcystins from sheep rumen contents are relatively straightforward. However, the recovery of microcystin from liver and tissue samples cannot be expected to be complete without the application of proteolytic digestion and extraction procedures. This is likely because microcystins bind covalently to a cysteine residue in protein phosphatase. Unless an effective procedure is applied for the extraction of covalently bound microcystins (and nodiilarins), then a negative result in analysis cannot be taken to indicate the absence of toxins in clinical specimens. Furthermore, any positive result may be an underestimate of the true amount of microcystin in the material and would only represent free toxin, not bound to the protein phosphatases. Optimized procedures for the extraction of bound microcystins and nodiilarins from organ and tissue samples are needed. 

Presently, only the molecular dynamics approach suffers from a computational bottleneck [58-60]. This stems from the inclusion of thousands of solvent molecules in simulation. By using implicit solvation potentials, in which solvent degrees of freedom are averaged out, the computational problem is eliminated. It is presently an open question whether a potential without explicit solvent can approximate the true potential sufficiently well to qualify as a sound protein folding theory [61]. A toy model study claims that it cannot [62], but like many other negative results, it is of relatively little use as it is based on numerous assumptions, none of which are true in all-atom representations. 

True negative rate probability that the test result is negative when the analyte is not present, A (i.e. equal or below the specification limit, respectively)... 

Table 4.3. Scheme of test results for screening procedures tp true positive,)p false positive, tn true negative, fn false negative, n total number of tests...

It is generally accepted that true polymorphism results in distinct optical and spectral properties. The data presented are entirely negative in these respects. The evidence accumulated agrees with the findings of Pfeiffer55 and questions the formation of aspirin polymorphs. 

The term capillary action describes the upward movement of a fluid as a result of surface tension through pore spaces. The fluid can rise until the lifting forces are balanced by gravitational pull (see Figure 3.28). The rise of fluid in a small tube above the water table surface, as previously discussed in Chapter 3, can be described using Equation 3.13. Lifting of fluids above the water table is a true negative pressure compared with atmospheric pressure (also described as soil suction). In soil situa-... 

The study then examines whether this is true. The amount of data needed to prove a difference between the samples depends on the size of the difference that is to be detected. Enough data must be collected to minimize the risk of a false-positive or false-negative result. This is determined by a power calculation. 

This is not a proper use of the phrase false positive. In bioassay terms, a result is said to be a false negative when a true positive effect is missed, and a false positive when a true negative effect is reported as positive. A cancer effect at an MTD is not a true false... 

An unaffected patient will have a negative DNPH result. Mildly affected or partially treated patients may also yield negative results. Patients with a blood phenylalanine level (indicative of PKU) over 1 mmol/1 should generate positive DNPH results. Patients with a blood leucine level (indicative of MSUD) of 0.8 mmol/1 or higher usually show a positive DNPH result. Patients with pyruvate metabolic disorders may also give positive results, as will patients with true and transient disorders of tyrosine degradation. 

The 76 variables derived from the DEC evaluation were first analyzed using stepwise discriminant analysis to determine the variables that best predicted the presence or absence of each drug. This subset of best-predictor variables was then subjected to a discriminant function analysis that predicted and classified whether subjects were dosed or not dosed with drug. The resulting data were classified as true positive, true negative, false positive, or false negative. These parameters were then used to calculate several measures of predictive accuracy of the DEC evaluation, including sensitivity, specificity, and efficiency. 

The immunohistochemistry of ERs has been exhaustively compared with the DCC assay. Review of the literature indicates -85% agreement between these two methods (Allred, 1999). This is true when immunohistochemistry is restricted to fresh-frozen sections. Immunohistochemistry of frozen sections compared with paraffin sections is a more specific test to detect ER-positive tumors with very low tumor cellularity the DCC assay gives false-negative results for such tumors. A number of publications have also reported good agreement between the DCC assay and immunohistochemistry of paraffin-embedded... 

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