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Points of significance

Sources of variation

Nature Methods volume 12, pages 5–6 (2015)Cite this article

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Abstract

To generalize conclusions to a population, we must sample its variation.

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Figure 1: Internal and external validity relate respectively to how precise and representative the results are of the population of interest.
Figure 2: In the presence of variability, the precision in sample mean can be improved by increasing the sample size, or the number of replicates in a nested design.

References

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Authors and Affiliations

  1. Naomi Altman is a Professor of Statistics at The Pennsylvania State University.,

    Naomi Altman

  2. Martin Krzywinski is a staff scientist at Canada's Michael Smith Genome Sciences Centre.,

    Martin Krzywinski

Authors
  1. Naomi Altman
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  2. Martin Krzywinski
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The authors declare no competing financial interests.

Integrated supplementary information

Supplementary Figure 1 A two-factor nested design scenario with different number of replicates and different variance at each layer.

For a given layer (e.g. mouse), also shown is the variance of the mean of observations for all deeper layers (e.g. cell + technical). Xijk corresponds to the k measurement of cell j from mouse i. Dots in the subscript correspond to average over those subscripts (e.g. Xi.. is the average of cell and technical replicates for mouse i).

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Supplementary Text and Figures

Supplementary Figure 1 and Supplementary Note. (PDF 145 kb)

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Altman, N., Krzywinski, M. Sources of variation. Nat Methods 12, 5–6 (2015). https://doi.org/10.1038/nmeth.3224

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