A quality analyst wants to construct a control chart for determining whether four machines, all producing the same product, are in control with regard to a particular quality attribute. Accordingly, she inspected 1,000 units of output from each machine in random samples, with the following results

MachineTotal Defectives#123#215#329#413

What is the estimate of the standard deviation of the sampling distribution of sample proportions for this process?

.016

.00016

.04

.0044

.00002