# Thread: Negative Binomial Regression - Is this scatterplot okay (pic)?

1. ## Negative Binomial Regression - Is this scatterplot okay (pic)?

Hi there,

One assumption of negative-binomial regression is linearity. I have this scatterplot of IV and DV?

Would you say that there is linearity? Is this scatterplot okay?

2. ## Re: Negative Binomial Regression - Is this scatterplot okay (pic)?

hi,
maybe orthers will disagree, but, nope, to me this looks like you would need additional explanatory variables. that bulge in the middle looks like something that would ruin your fit whatever method you used.

regards

3. ## The Following User Says Thank You to rogojel For This Useful Post:

Franziska13 (03-30-2017)

4. ## Re: Negative Binomial Regression - Is this scatterplot okay (pic)?

Originally Posted by rogojel
hi,
maybe orthers will disagree, but, nope, to me this looks like you would need additional explanatory variables. that bulge in the middle looks like something that would ruin your fit whatever method you used.

regards
Possibly. But as always it's hard to tell in situations like this. Sometimes the seemingly "extra" variance that occurs in the middle of the bulge is just due to sample size issues. When you have a lot of data it's more common to see those "larger" values.

Code:
``````set.seed(100)

nlow <- 5
nmid <- 1000
nhigh <- 20
n <- sum(nlow, nmid, nhigh)

xlow <- rnorm(nlow, 2.5)
xmid <- rnorm(nmid, 7.5)
xhigh <- rnorm(nhigh, 12.5)

x <- c(xlow, xmid, xhigh)

# Equal variance
err <- rnorm(n, 0, 1)
y <- 3 + x*1/15 + err

plot(x,y)``````

5. ## The Following 2 Users Say Thank You to Dason For This Useful Post:

Franziska13 (03-30-2017), rogojel (03-28-2017)

6. ## Re: Negative Binomial Regression - Is this scatterplot okay (pic)?

Many times I examine linearity using loess regression.

7. ## The Following User Says Thank You to hlsmith For This Useful Post:

Franziska13 (03-30-2017)

 Tweet

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts