Figure 1.

Scatter plot of the log₁₀ rpm in two samples. A. Scatter plot of the log₁₀ rpm in two samples. The greater spread at lower counts suggests higher variance. B. Sample variance of log₁₀ rpm from a simulation with constant biological variation shows that the increased sample variance may be caused by poor approximation of a Gaussian distribution to a Binomial distribution for sparse counts. To create the simulation dataset, we sampled log(π₀) from observed average log counts and created log(π₁) = log(π₀) + δ/2 and log(π₂) = log(π₀) - δ/2 where δ ~ N (0, σ²). In this plot σ = 0.122, as estimated in the example data.