Validity criteria, safety performance

According to lEC 61508 and lEC 61511 the safety validation should be performed in terms of the overall safety functions requirements and the overall safety integrity requirements, taking into account the safety requirements allocation for the E/E/PE safety-related system in designing. In particular PFDavg value has to be verified in the probabilistic modeling process for the architectures considered of the E/E/PE safety-related systems taking into accoimt the probabihstic interval criterion for selected SIL. 

In this subsection, we apply another type of safety performance data, i.e., self-reported staff attitudes to error reporting and interaction with the patient, to the test of criterion validity of the safety culture factors. For this purpose, we used the nurse sample of the Japanese data including more than 17,000 questionnaire responses collected from 82 hospitals (Itoh and Andersen, 2010). An example of resrrlts of correlation analysis is shown in Table 4.10 in terms of Spearman s rho, using the mild outcome case in the three vignettes offered - results for the near-miss and severe cases were quite similar to this case. 

Audit instruments can be evaluated on the basis of three different types of validity when linking the audit to safety performance. These are content-related, criterion-related, and construct-related procedures for accumulating evidence of validity (Anastasi 1988, 139). Content-related validity involves the examination of the audit content to determine whether it covers a representative sample of the behaviors to be measured. Criterion-related validity procedures indicate the effectiveness of an audit in predicting performance in specified activities. The performance on the audit is checked against a criterion that is considered a direct and independent measure of what the audit was intended to measure. The third type of validity, construct validity, is the extent to which the audit is said to be measuring a theoretical construct or trait. Construct validation requires accumulation of information from a variety of sources. 

For isothermal batch processes it is an exactly valid safety assessment criterion. The further discussion of the isothermal process can be performed in total analogy to the discussion of the isoperibolic process, except that Equ.(4-167) has to be used. An example of such a limit value diagram for isothermal BR has been calculated and is presented graphically in Figure 4-46. 

It is important that the tests employed detect bidirectional drug effects and be validated in both directions with appropriate reference (control) substances. This requirement is less appropriate for multiparameter procedures. Blind testing could be an advantage. Ethical considerations are important, but the ultimate ethical criterion is the assessment of risk for humans. Safety pharmacology studies should not be overly inclusive but should be performed to the most exacting standards, including GLP compliance. This is, of course, backward such human tolerance is properly an extension (and expression) of the nonclinical safety pharmacology. 

Validity relates to whether you are measuring what you want to measure. When we measure the width of a room, the question of validity usually does not arise. When we are measuring a complex process, such as aptitude to perform well in college or the ability of the safety-management system in a plant to prevent future loss, validity becomes a serious question. Scientists (Chronbach and Meeh 1955) generally define three categories of validity content-related, criterion-related, and construct-related validity. 

Validity is another question. We have said that audits typically have content-based validity. Testing for criterion-based validity may be beyond the scope of many situations for which safety professionals would like to apply audits. Certainly in a company with a small population and relatively low accident rates, there would probably not be enough data to find a relationship between audit scores and accident rates. An alternative would be to look for a relationship between audit scores and the scores on our safety survey (see Chapter 8). Since the scores of this survey are extensively validated as measures of system performance, they can serve as a criterion against which to test audits. 

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