Statistical power analysis for the number of cells. The plot shows means (dots) and 95% confidence intervals (vertical bars) of the measured effect on the proliferation rate of transfection with cyclin A (a positive control in the assay) as a function of the number of cells analyzed. The effect was measured by a robust local regression of the anti-BrdU intensity on the intensity from the YFP-tag (arbitrary fluorescence units). The dependence on the number of cells was simulated by random sampling from the full data set with 2211 cells. The red line represents the approximate true effect, and the blue line no effect. In this example, we would have detected cyclin A as an activator of cell proliferation with 95% probability only for cell numbers ≧1000. Conversely, we would have assigned an activating effect to a protein that is in fact neutral with <5% probability. To reliably detect modifiers of cell proliferation that are subtler, or to achieve probabilities better than 95%, cell numbers must be even higher.
