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To: cs551@merlot.usc.edu
Subject: Re: Unit for std deviation
Date: Wed, 24 Sep 2008 19:00:35 -0700
From: Bill Cheng <william@bourbon.usc.edu>

Some wrote:

  > In the spec it says to print 6 sig digits and it also says to print 3 digits
  > after the decimal place. Cant that be conflicting since significant digits
  > omit trailing 0's which means there might be less than 3 after the decimal
  > place?
  > 
  >   "All real values in the statistics must be printed with at least 6
  >   significant digits. A timestamp in the beginning of a line of trace output
  >   must be in milliseconds with 8 digits (zero-padded) before the decimal point
  >   and 3 digits (zero-padded) after the decimal point. 
  > 
  >   Please use sample means when you calculated the averages. If n is the number
  >   of sample, this mean that you should divide things by n (and not n-1). 
  > 
  >   The unit for time related statistics must be in seconds (and have at least 3
  >   digits after the decimal points)."

The first paragraph says that it must have at least 6 significant
digits.  The 3rd paragraph says that it must have at least 3
digits after the decimal point.  I think both rules should be
honored.

For example, if the statistics value you want to print is 123456,
then you should print 123456.000.  If the statistics value you
want to print is 3.14159265359, you should print 3.14159.
--
Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>





  -----Original Message-----
  From: Bill Cheng [mailto:william@bourbon.usc.edu] 
  Sent: Wednesday, September 24, 2008 6:20 PM
  To: cs551@merlot.usc.edu
  Subject: Re: Unit for std deviation
  
  Someone wrote:
  
    > Does standard devation value have a unit? I am using seconds. 
  
  Variance of X has the same unit as the square of X.
  Since standard deviation is the square of variance, standard deviation of X
  should have the same unit as X.
  --
  Bill Cheng // bill.cheng@usc.edu <URL:http://merlot.usc.edu/william/usc/>