# Actuarial Discussion Forum - Professional Discussions for Professional Actuaries

 D.W. Simpson & Co, Inc. - Worldwide Actuarial Jobs Life Jobs Health Jobs Pension Jobs Casualty Jobs Salary Apply Pauline Reimer, ASA, MAAA - Pryor Associates Nat'l/Int'l Actuarial Openings: Life P&C Health Pensions Finance ACTEX Publications and MadRiver Books Serving students worldwide for over 40 years Advertise Here - Reach Actuarial Professionals Advertising Information Actuarial Careers, Inc.® - Actuarial Jobs Worldwide Search positions by geographic region, specialization, or salary Ezra Penland Actuarial Recruiters - Top Actuarial Jobs Salary Surveys  Apply Online   Bios   Casualty   Health   Life   Pension

1. ## Negative Binomial

Can anyone please confirm if these formulas are correct for negative binomial, thanks.

pdf = [ (x+r-1) nCr (x) ](p^r) (q^x)
cdf = ∑ pdf
E(x) = r*q/p
var(x) = r*q/(p^2)
mgf = [p/(1-q*e^t)]^(x+1)

2. A good place to check wikipedia or mathworld.wolfram.com

3. I checked and they give me 2 different answer.
Thats why I want to verify if this is correct, thanks

4. Well wikipedia disagrees with you right?

Now in the mathworld link, it might look different but write out (x+r-1) C (r-1) and compare that to (x+r-1) C (x). You should be able to prove they are the same.

There are currently 1 users browsing this thread. (0 members and 1 guests)

#### Posting Permissions

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