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Sample size determinations using examples drawn from the NCTR Collaborative Behavioral Teratology Study data

Neurotoxicology and Teratology
Publication Date
DOI: 10.1016/0892-0362(89)90011-1
  • Behavioral Test Sensitivity
  • Coefficient Of Detection
  • Samples Size Determinations For Behavioral Teratology Data
  • Design


Abstract The Collaborative Behavioral Teratology Study (CBTS) introduced the coefficient of detection (CD) as an estimate of the minimum difference needed to detect a significant difference among groups. The CD was used to provide an index of the sensitivity of the tests used. As originally described, the CD is not suitable for estimates of two or more group minimally significant differences because it is based on a one-group formula. Also, the CD operates at a power of 50% in the one-group case (see preceding paper). These drawbacks leave questions about the sensitivity of the tests used in the CBTS unanswered. Using examples drawn from the CBTS data base, a more standard method of approaching this question has been taken here based on power calculations. Using the means and standard deviations from the vehicle controls, α = 0.05, 1− β = 0.80, and 20, 30 or 40% group mean difference sizes, required samples sizes were detemined for all the behavioral measures reported in the CBTS final report for Experiment 1. The results showed that most of the measures can detect 30% group mean differences in a two-group, two-tailed t-test situation with group sizes of ≤20 litters per group. More complex calculations are required when more than two groups are planned. Multigroup designs require additional assumption about the distribution of group differences and accordingly are more difficult to specify. However, based on the two-group case, it is concluded that the CBTS data can be used to support the idea that reasonable group differences can be detected with behavioral teratogenic methods using group sizes typical of safety assessment studies conducted for developmental and reproductive toxicity in rodents.

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