Evidence of absence

Iron-sulfur proteins can be observed by EPR spectroscopy, either in their oxidized or in their reduced state. As a method of observing iron-sulfur clusters, EPR is discriminating but not particularly sensitive lack of a detectable EPR signal cannot be taken as evidence of absence. However, a positive EPR signal is good evidence for the intactness of an iron-sulfur cluster in a protein. Moreover, EPR can be used to follow reduction of the clusters and, by use of mediated electrochemical titrations, to estimate redox potentials. 

A test of the null h)rpothesis that the rates of infection are equal - Hq x jii/hnj = 1 gives a p-value of 0.894 using a chi-squared test. There is therefore no statistical evidence of a difference between the treatments and one is unable to reject the null hypothesis. However, the contrary statement is not true that therefore the treatments are the same. As Altman and Bland succinctly put it, absence of evidence is not evidence of absence. The individual estimated infection rates are jTi = 0.250 and = 0.231 that gives an estimated RR of 0.250/0.231 = 1.083 with an associated 95% confidence interval of 0.332-3.532. In other words, inoculation can potentially reduce the infection by a factor of three, or increase it by a factor of three with the implication that we are not justified in claiming that the treatments are equivalent. 

One of the problems with the diagnosis and treatment of EPM is that the sensitivity and specificity of the tests available currently to diagnose this disease continue to be debated and antibodies to S. neurona may persist in the cerebrospinal fluid (CSF), making it difficult to evaluate treatment efficacy. A negative result on Western blot of a CSF sample is evidence of absence of infection (Daft et al 2002). It also indicates resolution of infection and is the most reliable predictor that a horse will not relapse if the treatment is discontinued. 

However, there is actually little published evidence to draw on and even if controversial evidence is accepted, the total burden of disease that can be potentially attributable to environmental contamination will be modest in comparison with the range of avoidable disease. However, this absence of evidence is different from evidence of absence and such an approach does not consider potential inequalities in risk distribution. 

Altman DG, Bland JM (1995) Absence of evidence is not evidence of absence. British Medical Journal 311 485. 

Thus, the assertion that rofecoxib could have been known to be worse than placebo by 2000 is based entirely on an auxiliary hypothesis that naproxen and placebo are identical. This hypothesis may or may not have been reasonable at the time, but the meta-analysis as carried out by Juni et cd. (2004) cannot prove it. To be fair to these authors, they did carry out some independent investigation of this hypothesis by looking at studies that had compared naproxen with placebo but here they assumed that absence of evidence was evidence of absence and did not use methods that have been developed for formally incorporating evidence regarding previous trials of comparators. (See the discussion of the approaches of Hasselblad and Kong (2001) and Hlrotsu and Yamada (1999) in Chapter 15). 

Nuclear forensics also plays a role with regard to the processing of uranium ore concentrates in the UCF and fabrication of uraninm oxide for fueling nuclear reactors or of uranium hexafluoride for isotope enrichment facilities. Characterization of the nuclear materials can detect unauthorized operations and partially ascertain that no undeclared activities are taking place but one shonld always bear in mind that absence of evidence is not evidence of absence. In some cases, relevant information may be obtained from bulk samples but highly significant details may be found in analysis of single particles. Some examples will be presented here, but more details are discussed in Section 5.4. 

Frame 5.1, based on fictional literature, demonstrates the importance of nuclear forensics and the implications of carrying out a timely and accurate analysis. In addition, the quote opening this chapter (absence of evidence is not evidence of absence), although totally unrelated to nuclear forensics, should always be on our minds when results of analyses are reported. 

The authors of a review focused on the concern about resistance to anthelmintic agents note that while resistance alleles have been noted in helminthic populations in humans, it has never been demonstrated that these alleles increase in frequency following treatment or spread within the population. [5 ] Although there are documented instances of reduced efficacy in the form of decreased cure rates and decreased egg reduction rates (possibly indicating resistance), the authors in that review raise concern over numerous methodological issues present in those studies. We caution that the absence of evidence does not confirm evidence of absence with regard to drug resistance. It seems somewhat ironic that our inadequate efforts to eradicate worm infections... 

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