# Random sample and confidence intervals

• Jul 6th 2010, 10:56 AM
losm1
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)?
• Jul 7th 2010, 08:00 PM
pickslides
What confidence and error width do you deisre in the sample size?
• Jul 8th 2010, 08:33 AM
losm1
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)
• Jul 8th 2010, 03:10 PM
pickslides
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.