# Finding the confidence interval

## Homework Statement

What formula do I need to find the confidence interval, when I have got:

- Number of samples
- Level of Confidence
- The assumed (1st guess) accuracy

## Homework Equations

I found the following equation online: µ = z * [p * (1 - p) / n] ^ (-1/2)

## The Attempt at a Solution

When I fill in this formula, I get µ = 125.5, while I think the confidence interval should be around 3 percent.

rock.freak667
Homework Helper
If you want a 95% CI, then you want P(-a<Z<a)=0.95 where

$$Z=\frac{\bar{x}-\mu}{\frac{\sigma}{\sqrt{n}}}$$.

So $\bar{x} \pm a \frac{\sigma}{\sqrt{n}}$ will be a 95% CI for μ

Mark44
Mentor

## Homework Statement

What formula do I need to find the confidence interval, when I have got:

- Number of samples
- Level of Confidence
- The assumed (1st guess) accuracy

## Homework Equations

I found the following equation online: µ = z * [p * (1 - p) / n] ^ (-1/2)
This may or may not be relevant to your problem. This formula looks vaguely related to a binomial distribution. You haven't said what the distribution is, so it's hard to say if this is something you need to use.

## The Attempt at a Solution

When I fill in this formula, I get µ = 125.5, while I think the confidence interval should be around 3 percent.

Again, you have provided enough information for me to tell if this is a reasonable value for µ. What you said about the confidence interval makes no sense at all. A confidence interval is an interval, with a left endpoint and a right endpoint. It is not given as a percentage.

All the information I have got considering this practice situation:

Information written down on a form will be put in a database. The information in the database can be correct (match the information written on the form) or can be incorrect (do not match the information written on the form). A mismatch occurs when the database administrator enters the wrong information (for example: putting "b" in the database when "a" is written on the form).

Now I would like to execute a sample to judge whether the data found in the database is reliable (ie consistent with the source information) or not. The database contains a total of 4000 entries. I would like to execute a sample because it is quite time consuming to check if all 4000 entries are correct or not. With this sample I would like to state something about the reliability of the entire database (4000 entries).

So, suppose I have 100 entries checked, and 2 of them do not match. Then I find that 98% of the database entries of the corresponding sample is consistent with the source information. But what can I say about the confidence level and interval of this 98% considering the entire database (4000 entries).