# How to calculate greater than or equal to in R using ppois? [closed]

I am trying to calculate P(x>=3) using R. What I wrote is the following;

ppois(3,4.5) #this returns 0.342296


the problem here is that the value is for (Px<=3). I know that including "lower = FALSE" will return P(X>3)

ppois(3,4.5,lower=FALSE) #This returns 0.657704 which is P(X>3)


What would I have to modify or include to return P(X>=3)?

Note that $$P(X \ge 3)$$ is equivalent to $$P(X > 2)$$

We can then calculate the following probability as follow: $$$$P(X > 2) = 1-P(X \le 2) = 0.8264$$$$

We can then compute the desired probability using R:

# P(X>2)
ppois(2,4.5, FALSE)

#OR

# 1-P(X<=2)
1-ppois(2,4.5)


Output:

0.8264219


As a side note - RStudio is a R Integrated Development Environment (IDE)

• there is also the argument lower.tail=FALSE to ppois to save you the 1 -  part. – JDL Nov 5 '20 at 12:04