CODEWITHSUNDEEP
rprobability
CClarke
CClarke

Reputation: 576

Is R's pgeom function incorrect?

Let's say I have an event that has a probability of 0.02 of occurring each time a button is pushed. I want to calculate the probability that the event will occur the 8th time someone presses a button.

I can calculate this manually with 0.98^7 * 0.02 as 0.017 but if I use pgeom(q = 7, prob = 0.02) in R I get 0.149237. How can this be? I'm sure I'm missing something but I can't figure it out!

Upvotes: 2

Views: 198

Answers (1)

Jan
Jan

Reputation: 5254

Try 

dgeom(7, 0.02)
# returns 0.01736251

The geometric formula p*(1-p)^x descibes the density function dgeom. pgeom, however, does not compute the density but the lower-tail of the distribution.

Upvotes: 3

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