# Thread: Confidence level

1. ## Confidence level

Hello,

Simulating a queue doing 100 times. Confidence level is 95% and Confidence interval is (413s,425s) for average response time.
What is standard division?

Thanks

2. ## Re: Confidence level

Assuming the question is instead "What is the standard deviation?"

Hint: Given a high number of samples, we can assume the graph is approx. a normal distribution. From here, we can calculate the z-score for a confidence level of 95%. Can you take it from here?

3. ## Re: Confidence level

Originally Posted by MacstersUndead
Assuming the question is instead "What is the standard deviation?"

Hint: Given a high number of samples, we can assume the graph is approx. a normal distribution. From here, we can calculate the z-score for a confidence level of 95%. Can you take it from here?
Thank you,

4. ## Re: Confidence level

Just to confirm, you have to use the z-score for the final calculation of the standard deviation. I didn't want to give away too much so you could figure out the rest of the answer. Let me know if you need more help on that.

5. ## Re: Confidence level

Thanks, with which formula ?
Now we have n = 100 , Confidence level is 95% and confidence interval is (413s,425s).
With which formula we can calculate SD?

6. ## Re: Confidence level

With a calculated z-score of 1.96, this means we have a graph like this

ie. The upper limit is 1.96 standard deviations from the mean. The lower limit is -1.96 standard deviations from the mean.

From here, you should be able to answer the following:
(i) What is the mean of your confidence interval? (call this x)
(ii) What is the standard deviation from the mean? ie. If 1.96 standard deviations is the difference between x and 425s, what is 1 standard deviation?

Answer i and ii and you are done. Once you understand the process, feel free to use a compact formula like 1 SD = (b-a)/(z-score) where (a,b) is your confidence interval.

7. ## Re: Confidence level

Originally Posted by MacstersUndead
1 SD = (b-a)/(z-score) where (a,b) is your confidence interval.
Typo. 1 SD = (b-(mean))/(z-score)

where the mean is a + (b-a)/2