A Quality Analyst wants to construct a control chart for determining whether errors in bank transactions are under control. She looked at samples of 1000 transactions each week, for four weeks in a row. A transaction was considered defective, if the analyst detected any error in the transaction.

Week Total Defectives

1 50

2 27

3 15

4 35

What is the standard deviation of the sample proportions of defective transactions?

.0056 .0025 None of the other options are correct .0148 .0500