[R] Question regarding dnorm()

[S Ellison]

You have calculated density, not probability.

Probability is in [0,1]; density is in [0,Inf)  

And for a continuous variable, density cannot be interpreted as a probability or a frequency.

S


> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Vincy Pyne
> Sent: 14 September 2011 12:24
> To: r-help at r-project.org
> Subject: [R] Question regarding dnorm()
> 
> Hi,
> 
> I have one basic doubt. Suppose X ~ N(50,10).
> 
> I need to calculate Probability X = 50.
> 
> dnorm(50, 50, 10) gives me
> [1] 0.03989423
> 
> My understanding is (which is bit statistical or may be 
> mathematical) on a continuous scale, Probability of the type 
> P(X = .....) are nothing but 1/Infinity i.e. = 0. So as per 
> my understanding P(X = 50) should be 0, but even excel also 
> gives 0.03989422. Obviously my understanding is wrong. If I 
> put value of x = 0 in the normal density function, I do get 
> 0.03989422.
> 
> My confusion is on the continuous scale if the probability (X 
> = x) doesn't make sense, 0.03989423 is significant to neglect.
> 
> Please clarify
> 
> Regards
> 
> Vincy
> 
> 
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