
Advanced Statistics Advanced Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
June 20th, 2007, 03:57 PM  #1 
Senior Member Joined: Dec 2006 From: New Jersey Posts: 378 Thanks: 1  Standard Deviation
A Police department reports the probabilities that 0,1,2,and 3 burglaries will be reported in any given day are 0.46, 0.44, 0.08, and 0.02, respectively. Find the Standard Deviation for the Probability Distribution. Round to nearest hundredths. 
September 5th, 2007, 08:47 AM  #2 
Member Joined: Aug 2007 Posts: 93 Thanks: 0 
Perhaps number of burglaries per day is best modelled with a Poisson distribution where the variance is equal to the mean, but using your numbers: x = 0,1,2 3 E(x) = Sum (x * p(x)) = 0.66 the Variance is Sum ( (E(x)  x)^2*p(x)) = 0.50 So the standard deviation is 0.50^.5 = 0.71 
September 5th, 2007, 01:12 PM  #3  
Global Moderator Joined: May 2007 Posts: 6,732 Thanks: 689  Re: Standard Deviation Quote:
The variance can be calculated as the second moment minus square of first moment. First moment (mean) = .46*0+.44*1+.08*2+.02*3 Second moment=.46*0+.44*1+.08*4+.02*9 I'll let you do the arithmetic.  
September 6th, 2007, 07:23 AM  #4 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms 
So are we supposed to assume that the police department is reporting the population probabilities rather than a sample probability?

September 6th, 2007, 08:00 AM  #5  
Member Joined: Aug 2007 Posts: 93 Thanks: 0  Quote:
 

Tags 
deviation, standard 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Help Please with Standard deviation.  adz_skim  Advanced Statistics  4  January 30th, 2014 07:43 PM 
Standard deviation  milly2012  Advanced Statistics  3  April 29th, 2012 08:21 PM 
Standard Deviation  bilano99  Algebra  3  March 21st, 2012 10:20 PM 
Standard deviation VS Mean absolute deviation  Axel  Algebra  2  April 28th, 2011 03:25 AM 
Standard Deviation  jbenloulou  Advanced Statistics  3  June 26th, 2009 06:11 AM 