# P-value for a regression where expected slope is 1:1

#### drm258

##### New Member
Hi, I am comparing two values for vegetation cover from two time periods. The expected value is y=x for the slope. I am curious how to calculate a p-value for this since the standard regression software is comparing the slope to zero, right? I could subtract the pre from the post, but then what would I put on the x-axis?

Thank you so much for your help!

#### hlsmith

##### Omega Contributor
So they have a perfect correlated relationship? Provide some more info please. If you want to compare a value to something other than 0 you just need to write a estimate statement. I believe its just like doing a one-sample ttest.

#### drm258

##### New Member
So they have a perfect correlated relationship? Provide some more info please. If you want to compare a value to something other than 0 you just need to write an estimate statement. I believe its just like doing a one-sample ttest.
Thank you for the response! My do not have an exact 1:1 relationship, but that would be the expected relationship given no change in other variables. Is there a way to write and estimate statement in Minitab? I tried to google it and was a little confused. I apologize, I am a student and still really shaky with my understanding of statistics and ability to speak the language. I sincerely appreciate the help though!

#### CowboyBear

##### Super Moderator
Do you mean that you want to test a null hypothesis that the slope is exactly one? If so you can calculate the t-test statistic as (estimated slope - 1)/SE rather than (estimated slope/SE).

#### hlsmith

##### Omega Contributor
Right on CB, glad to see I am finally figuring this stuff out after inundating myself.

What about a -1 slope or how are you planning to interpret the result (two-tailed)?

#### drm258

##### New Member
Do you mean that you want to test a null hypothesis that the slope is exactly one? If so you can calculate the t-test statistic as (estimated slope - 1)/SE rather than (estimated slope/SE).
Thank you!