# Thread: Random sample and confidence intervals

1. ## Random sample and confidence intervals

Company has n=5,000,000 customers that are using service X. We need to determine customer satisfaction with service X through phone survey.

Is there a formal way to determine optimal sample size (assuming that all calls will be answered)?

2. What confidence and error width do you deisre in the sample size?

3. 95% confidence, i don't know what error width is. (you can choose any appropriate error, I'm interested in approach, not just result for this specific case)

4. It's good you have identified the confidence level required. The error width will be how far either side of this you can allow for.

$95\% \pm 3\%$ will require more samples than $95\% \pm 5\%$

Have a read of this guy.

PEOD6/PD006: Determining Sample Size

There is a table at the bottom that will give you some numbers to consider.