# Confidence Interval VS Level of signficance?

#### greyghost

##### New Member
Hello,

I'm working on a question where part 'a' states to set up a confidence interval and part 'b' asks if there is difference that the means are significantly different. I thought they used the same alpha value...i think i might be misinterpreting the question, i can post it if needed. thanks a lot for taking a look at this.

#### Dragan

##### Super Moderator
Hello,

I'm working on a question where part 'a' states to set up a confidence interval and part 'b' asks if there is difference that the means are significantly different. I thought they used the same alpha value...i think i might be misinterpreting the question, i can post it if needed. thanks a lot for taking a look at this.
You might want to put the question up because people will be left to "read into" your question.

For example,

Under the null: H0: Mu1 - Mu2 = 0

Next, I compute a confidence interval based on an alpha level of e.g. 0.05 and get something like:

+LowerLimit <= Mu1 - M2 <= +UpperLimit.

If this interval is based on the alpha level in part (a), then I would reject H0 in part (b) because, obviously, zero doesn't lie between two positive numbers.

On the other hand, if my confidence interval were (based on alpha 0.05)

-LimitLimit <= Mu1 - M2 <= +UpperLimit

then I would fail to reject H0 in part (b) because zero lies between a negative number and a postive number.
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I may have even answered your question - but I cannot say for sure.