SOLUTION: Thank you for being there! I'm numerically-challenged and plagued by instincts I can't make work for me. I am trying to calculate an overall aggregate recidivism rate for three d

Question 1995: Thank you for being there! I'm numerically-challenged and plagued by instincts I can't make work for me. I am trying to calculate an overall aggregate recidivism rate for three distinct groups of kids. Each group has a distinct recidivism rate, but I need to meld them into an overall average weighted rate. Here are my numbers for your pleasure (pleasure?):
17 kids with a 12 percent recidivism rate
19 kids with a 37 percent recidivism rate
22 kids with a 55 percent recidivism rate
Question? What is the average recidivism rate for all these 58 kids?
I'll treat you to lunch if you can back to me quickly; I'm preparing a summary report for our judges and there ain't a mathematician in the courthouse! WP, administrator of Re-Entry Court.
wally9542@cox.net
Answer by longjonsilver(2297) (Show Source): You can put this solution on YOUR website!
forgive my lack of legal jargon :-)
Group1: number of recids/17 = 0.12 --> no recids = 2 in this group
Group2: number of recids/19 = 0.37 --> no recids = 7 in this group
Group3: number of recids/22 = 0.55 --> no recids = 12 in this group
so combined, total number of recids = 21
and total number of offenders = 58
so mean value = (21/58)*100 = 36%
NEVER EVER EVER EVER just add the 3 means and divide by 3...the 3 sets have different sizes and so their is a weighting.
Jon.
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