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Guidelines for the Care and Use of Mammals in Neuroscience and Behavioral Research (2003) / Chapter Skim
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Appendix A: Sample Size Determination
Pages 175-180

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From page 175...
... Sometimes, the number of animals to be used can be estimated best from experience; more often, a simple sample-size calculation should be performed. Even complicated experimental designs requiring sophisticated statistical models for analysis can usually be simplified to a single key or critical question so that simple formulas can be used to estimate the required sample size.
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From page 176...
... Note: the smaller the difference the investigator wishes to detect or the larger the population variability, the larger the sample size must be to detect a significant difference. EFFECT SIZE, STANDARD DEVIATION, POWER, AND SIGNIFICANCE LEVEL In general, several factors must be known or estimated to calculate sample size: the effect size (usually the difference between two groups)
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From page 177...
... Using, for example, randomized block, Latin square, or factorial experimental designs and the analysis of variance, it is possible to control for the effect of strain differences on such a factor as survival or response to an intervention and to obtain a more significant result than would be possible with more elementary methods. However, the simplified designs discussed here yield sample sizes close to what would be obtained with more complex analyses and therefore should help the investigator to be self-sufficient in planning experiments.
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From page 178...
... CALCULATING SAMPLE SIZE FOR REPEAT STUDIES Estimates of required sample size depend on the variability of the population. The greater the variability, the larger the required sample.
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From page 179...
... SAMPLE SIZE FOR TIME TO AN EVENT The statistical analysis of time to an event involves complicated models; however, there are two simple approaches to estimating sample size for this type of variable. The first approach is to estimate sample size by using the proportions of the experimental groups that exhibit the event by a certain time.
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From page 180...
... , but it cannot be used if some animals do not reach the event during the study. To compute sample size, it is necessary to obtain the estimate of the standard deviation of the variable (s)
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Key Terms

  • investigator wishes
  • continuous variables
  • population standard
  • blood flow
  • calculating sample

  • required sample
  • effect size
  • compute sample
  • body fluid
  • paired study

  • dichotomous variables
  • body weight
  • experimental designs
  • flow rate
  • experimental intervention

  • yield sample
  • physiologic function
  • estimating sample
  • simple formula
  • statistics books

  • designs discussed
  • involves complicated
  • sophisticated statistical
  • rats spontaneously
  • calculate sample

  • estimate sample
  • simple approaches
  • latin square
  • previous experiments
  • elementary methods


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