# how to determine correct sample size?

I have 2,000 transactions and I have to check the accuracy of those transactions. I want to select a sample, check all transactions in this sample and make conclusions on population with 95 percent of confidence level. is there any formula for selecting the correct sample size? Please also give me advice about how to make a conclusion on the population.

• What exactly does it mean for a transaction to be accurate? Defining this will go a long way towards answering your question.
– Dave
Sep 26, 2019 at 20:50
• In addition to the question that @Dave asks, what fraction of transactions do you expect to be inaccurate, and how narrow do you need your 95% CI to be? For example, if you expect 5% to be inaccurate, would 95% CI of 1%-9% be adequate, or do you need something tighter like 4%-6%?
– EdM
Sep 26, 2019 at 21:44
• in my case accurate means that all parameters of transactions were specified correctly. inaccurate means at least one parameter in transaction is incorrect. @EdM I have no idea how much of transaction are accurate. confidence interval of 1-9 % would be adequate. Sep 27, 2019 at 7:31