# Thread: Intercept becoming negative(More IDVs)

1. ## Intercept becoming negative(More IDVs)

Hi All,
I have a small query.

When regressing revenue against cost, my intercept is positive for X% combos where each combo consists of data points at weekly level for Region x Product x Channel. When i am adding more variable into the regression equations, i see many combos now having negative intercept when regressing revenue against cost and a few more IDVs.

Can someone explain as to why this is happening and what can be inferred from it??

Thanks & Regards

2. ## Re: Intercept becoming negative(More IDVs)

Do you know what the intercept represents?

Can your dependent variable take on a negative value?

Does your dependent variablr take on a negative value in the dataset?

3. ## Re: Intercept becoming negative(More IDVs)

Well my DV is the revenue. It should not be negative. No we had no cases in the data set where in the DV i.e. the revenue was negative. Let's say i am running a regression with Revenue as DV and Cost as IDV then it would mean a negative renvenue in case the cost is zero.

4. ## Re: Intercept becoming negative(More IDVs)

A negative intercept means predicted y takes on a negative value when predictors equal 0 or reference value. Look up extapolation and check back here.

5. ## Re: Intercept becoming negative(More IDVs)

Originally Posted by vikash_124124
my DV is the revenue. It should not be negative. we had no cases in the data set where in the DV i.e. the revenue was negative.
Since this has been brought up, I've always wondered:
Let's say you have a DV value that can't go negative but, e.g., you have only a few values so the unreliable regression line shows that it does.
Both X & Y axes start at zero.

Can you justify somehow causing a positive value for the DV such that it causes the regression line to go exactly through zero?
It's what
you know to be true vs. what your graph shows.

If so, is this "fudging", or "sanitizing", or just plain illegal?

TIA

6. ## Re: Intercept becoming negative(More IDVs)

I know you can do it. You can also run models without intercept. Though I am not versed in these things.

Typically you cant generalize to data not in your variable 's range.

7. ## Re: Intercept becoming negative(More IDVs)

If I correctly understand the problem:

For X = 1 & 3, and Y = 1 & 7, m (the slope) = 3, and b (the Y intercept) = -2.
Now add an X value = 0 and a Y value such that the intercept = 0.

I haven't yet done the closed form solution, if it is possible, but by tweaking a spreadsheet for my simple example an added Y value of 0.8 gives an intercept of 0.000.

I used
http://hotmath.com/hotmath_help/topi...-best-fit.html

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