[R] distributional properties of rnorm

[Marc Feldesman]

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
http://odin.pdx.edu/~h1mf

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