>>>Say I have a set of data that is the price of a home.
>>>
>>>100,000
>>>125,000
>>>92,000
>>>175,000
>>>135,000
>>>10,000
>>>500,000
>>>
>>>Well, I know that the 10,000 fiqure is really just for a lot. So when figuring trends, I need to throw it out. I also know that the 500,000 fiqure is also way off, so it too needs to be thrown out.
>>>
>>>If each of these numbers were in a field in a dbf(one per record) How could I programmatically throw out numbers that were way off? I have tried diffrent forms of average and standard deviation, but nothing seems quite right. I need some high school algebra or statistics lessons I think.
>>
>>Well, some things you are leaving out. Will there always be a low and high which will need to be dropped out? Can you setup a simple range to compare values record to record. Setup an index on value and determine the difference between the numbers to establish a reasonable range. If a number falls way-out of the range then drop it. Is there another field that can be used to identify stuff to exclude. How do you know that $10,000 is a lot value? htwh
>
>
>Yes, most of the time there would be a high and low, but sometimes just one or the other. I know that the low number is a bad price logically. If all homes next door to one another are selling for x average, then one that is 10,000 is way below. No, there is not another field I can use.
>
>My basic question is, what is an exceptable range to include statistically? the middle 80%, the middle 40%, etc.

bryan,

imho, and depending on the size of the sampling of data, i would think that plus or minus 20-25% of the average would be a reasonable threshhold of acceptable values for the type of stats that i think you are talking about..

    average = sum sale.price / num.of.recds
    high.range = average + (average * .20)
    low.range = average - (average * .20)
    
    goto top
    do while not eof()
       if sale.price > high.range or sale.price < low.range
          *** record should not be used ***
       else
          *** do whatever you wish to do with the record ***
       endif
       skip
    enddo

hth