Normal Pdf

[Neville Windsor]

It was pointed out to me a few days ago that the N-Spire calculator has a normPdf function. For example, it gives normPdf(0,0,1)=0.398942 (this means , I assume, that the probability of obtaining the outcome 0 from a normal distribution with mean 0 and standard deviation 1 is 0.398942) but this doesn't make sense. Since the normal distribution is continuous, the probability of obtaining any specific value has to be zero. What is normPdf evaluating? I might also point out that the Casio Classpad apparently does the same thing (so I'm told - I don't have one).
Neville Windsor
Hellyer College
Burnie, Tasmania

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[John Hanna]

Neville,
See http://en.wikipedia.org/wiki/Probability_density_function

John Hanna
jeh...@optonline.net
www.johnhanna.us
T3 - Teachers Teaching with Technology
"A cowchip is paradise to a fly."

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[Marc Garneau]

normPdf returns the normal probability density function (who's graph is
the normal curve), so normPdf(0,0,1) means the standard normal curve
(mean=0, sd=1) has a height of about 0.4 when x=0. The probability
(represented by the area under the normal curve) is given by normCdf (C
stands for cumulative). Its syntax requires an interval (a,b). So the
probability that a random variable x of a normal distribution exists
between 'a' and 'b' is calculated by normCdf(a,b,mean,sd).

Marc Garneau

[Neville Windsor]

Thanks for the responses. I should have realised what it was evaluating, because 1/sqrt(2pi) is in fact 0.398942. Now I can answer those who asked me.

Marc Garneau

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[Ray Fox]

It is especially useful for graphing. Try f(x)=normpdf(x).

 

Ray