[R] distributional properties of rnorm

Marc Feldesman feldesmanm at pdx.edu
Thu Aug 24 03:05:10 CEST 2000

I've been trying to generate a series of random normal distributions using 
the rnorm function.  After I generated the first set:

set1<-rnorm(150, 505.5, 15.2)

I checked the mean and standard deviation of set1.  I was surprised to find 
the mean at 502.37 (rounded) and the standard deviation at 13.3 (again, 
rounded).  While I know that it is unrealistic to expect the distribution 
of the simulated data to match the given mean and standard deviation, I 
expected the results to be closer.  I then generated 20 more samples.  In 
no case did the mean exceed 505.5 (the highest value was 504.8).  The 
standard deviation ranged from a low of 12.4 to a high of 18.

Am I being unrealistic in expecting the results to approximate the given 
values of the mean and standard deviation?

Dr. Marc R. Feldesman
Professor and Chair
Anthropology Department
Portland State University
Portland, Oregon 97207

email: feldesmanm at pdx.edu

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