# Test of single proportion - how do i know population proprotion?

I have a study where I did a sample size calculation using N=2800, CI=95%, margin or error = 3.5% to yield n=613.

In the study (auditing of charts), I wanted to look at the error rate in my sample. I came up with 41 errors so p=41/613=0.067

I want to know if this proportion is significantly higher than what I should expect so I thought I could use the test of single proportion, however, to calculate this, I need both my sample proportion (p) and my population proportion (pi).

My question is --> how do I know my population proportion? Is it the same as the margin of error? Maybe I'm using the wrong formula even?

• The crucial element missing from this post is the value of "what I should expect." What is it? (We can't tell you, nor can we calculate it: it depends on the study and its objectives.) – whuber May 28 '15 at 22:15
• Yes, you're right. I don't know what I should expect, so this is probably not the right calculation for this study. Thanks for confirming. – kristayyc May 28 '15 at 22:17