Historical control data

FIGURE 4.2. Setting thresholds using historical control data. The figure shows a Gaussian ( normal ) distribution of screen parameters 99.7% of the observations in the population are within three standard deviations (SD) of the historic mean. Here the threshold (i.e., the point at which a datum is outside of normal ) was set at Xc = mean + 3 SD. Note that such a screen is one-sided. 

For other parameters, though, statistical analysis is just one of several considerations that include historical control data and other relevant information about the test agent and related test agents. For example, statistical analysis of a low incidence of... 

The availability of an adequate historical data base is often cited as an important criterion for species/strain selection. Historical control data can sometimes be useful... 

Although methods are available for including historical control data in the formal statistical analysis (Tarone, 1982 Dempster et al., 1983 Haseman, 1990), this is usually not done and for good reason. The heterogeneity of historical data requires that they be used qualitatively and selectively to aid in the final interpretation of the data, after completion of the formal statistical analysis. Table 9.3 presents a summary of background tumor incidences for the most commonly employed rodent strains. 

Haseman, J.K., Huff, J. and Boorman, G.A. (1984b). Use of historical control data in carcinogenicity studies in rodents. Toxicol. Pathol. 12 126-135. 

The number of alternative species in fact is limited by reasons of practicality of handling and the absence of relevant historical control data (see below). The most common alternative rodent is the mouse, for which sufficient data are available. When using mice, care should be taken since this species (unlike rats) is prone to... 

The wording cited above from the Guidance Document is selected very carefully and there is not too much to add. Generally, historical control data should be collected and adequately documented in each laboratory, and their usefulness is selftevident. For exceptional cases like very rare malformations even the use of historical control data from other laboratories may be appropriate (these are most unlikely to be caused by specific housing conditions). However, a clear and unequivocal study will always be one which exclusively refers to current control data. If this is not the case, then the use of historical control data may help clarifying open questions, but the study will normally be classified as grey zone. ... 

The current historical control data from Ricerca Biosciences are presented in Tables 2, 3, 4, 5, 6, 7, and 8. 

Historical control data for embryo-fetal studies at Ricerca Biosciences with CrI OFA SD Rat Caesarean data collected on day 20 of gestation... 

Since teratology studies in mice are far less frequent than in the rat, the amount of recent historical control data may be limited. If little or no recent reference data are available, the size of the concurrent control group should be increased. 

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