Sample Size Estimation Problem

I am trying to use a program called EZ-Quant to determine a sample size.

The program first asks you to choose one of the following options:
1. Judgmental assessment of universe error rate, or
2. Sample results from a similar audit universe.

I am selecting #1 because I don't have a similar audit universe.

After this, the program asks for a "Presumed Universe Error Rate."

The program explains this assessment is judgmentally derived from the percentage of the universe amount that is in error. It says the maximum is 50 percent.

I don't understand how I should come up with this number and need help.

Here is some background on what I'm trying to do.

I want to select a statistical sample from a list of transactions.
Once the sample of transactions is selected, each transaction in the sample will be examined for a certain type of error. I can go into more detail about what is being examined and what constitutes an error if need be but for now, I will just say, the transaction is either correct or in error.

The errors will then be projected onto the universe.

I initially looked at 4 transactions and found 2 of the 4 to be in error. Based on this, I am inclined to go with the 50% maximum error rate but I really don't know.

Any help would be most appreciated.


TS Contributor
this is just as you supposed, your original rough estimate of the error rate. Because the formula includes the term p(1-p) you get the largest sample size by assuming p=0.5.

rogojel, thanks for your reply. I would like to have a smaller sample. Therefore, I would like to input a smaller error rate but I would have to support this action and the number itself. Not sure how I could justify a smaller error rate.


TS Contributor
without data you cant really work on your error rate estimate - as an alternative you could input into the program different sample sizes and see what would be the precision of your measurement using that number of samples.

I have data and I have calculated the basics on it. Number of items, mean, mode, SD... I just need some guidance on coming up with a good error rate. I also need to figure out the desired max. precision amount which this programs says is equal to 1/2 the width of the sample projections confidence interval. Can someone put this is a way I can understand?