Determining sample size for dot grid estimates Graph 3-1. The graph below shows the general shape of a sample size power curve.
Power is plotted on the vertical axis and sample size is on the horizontal axis.
You can see from the graph that power increases with increasing sample size, but the slope of the curve decreases progressively as sample size increases, that is, you reach a point of diminishing returns. For a given level of power, a larger sample size is needed to obtain a higher confidence level. You can see that progressively larger sample sizes are needed to obtain a given level of power as the proportions approach 0.5.