HP Forum Archive 11

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Statistical Bug? Message #1 Posted by Trent Moseley on 26 Mar 2003, 4:02 p.m. Is there a bug in the standard deviation statistical function of some HP machines but not in others? Of the HPs I have with the stat function the 12C,15C, and the 42S seem to have the bug. The 25C, 67, and the 32SII do not. Here is the problem: With the summation key enter in several data and find the standard deviation. Next subtract a datum. Finding the SD now gives an error message. c cC

Re: Statistical Bug? Message #2 Posted by R Lion on 26 Mar 2003, 5:06 p.m., in response to message #1 by Trent Moseley I don't know if I understand you. I usually get mean, then sigma+ and get SD. Then mean again, sigma-. If I get SD now, I don't get any error message. Could you give any example? Raul

Re: Statistical Bug? Message #3 Posted by Trent Moseley on 26 Mar 2003, 6:14 p.m., in response to message #2 by R Lion For example: clear sigma+ 9 sigma+ see 1 15 sigma+ see 2 11 sigma+ see 3 take std dev see 3.06 11 sigma- see 2 take std dev see Error 2 on the 12C, 15C Stat Math Error on the 42S You do not get an error message on the 25C, 67, or 32SII but see the answer: 4.24

Re: Statistical Bug? Message #4 Posted by R Lion on 26 Mar 2003, 6:31 p.m., in response to message #3 by Trent Moseley You can avoid the problem introducing 0 as y data: 0 enter 9 sigma+ see 1 0 enter 15 sigma+ see 2 0 enter 11 sigma+ see 3 etc... and you'll get the expected answer Raul

Better solution Message #5 Posted by R Lion on 26 Mar 2003, 6:35 p.m., in response to message #4 by R Lion When you get one of those strange errors, STOre a 0 in regs 5, 6 and 7 (sumy, sumy^2 and sumxy). Then, s will work Raul

Re: Better solution Message #6 Posted by Trent Moseley on 26 Mar 2003, 6:55 p.m., in response to message #5 by R Lion Raul Lion, I don't bother. I use one of the machines that don't have the problem. tm

Re: Better solution Message #7 Posted by R Lion on 26 Mar 2003, 7:03 p.m., in response to message #6 by Trent Moseley Oh well... then send me your 15c and I'll send you a new 32sII ;-) Raul

Re: Better solution Message #8 Posted by Trent Moseley on 26 Mar 2003, 11:28 p.m., in response to message #7 by R Lion Raul, I love 'em all! The 16C didn't even get into the discussion! Now if only I could get my hands on a 34C! Trent

Re: Statistical Bug? Message #9 Posted by Les Bell [Sydney] on 26 Mar 2003, 6:40 p.m., in response to message #3 by Trent Moseley It happens as you describe on the 41CX, as well, but the reason is simple - it's the data in the Y register. When you get the SDEV result in X, then simply key in 11 and press sigma-, it will have 3.06 in the Y register, which it subtracts from the cumulative stat registers (which will have zero for both sigma Y and sigma(Y^2), from memory). If you key in a zero before the 11 to be sigma-minussed, or clear the stack, it will work just fine. Best, --- Les [http://www.lesbell.com.au]

Re: Statistical Bug? - not on my machine Message #10 Posted by Gene on 26 Mar 2003, 5:07 p.m., in response to message #1 by Trent Moseley Think you'll need to give more specifics. Which mode is the 42s in? LinSUM or ALLSUM? Did you do a CLEARSUM before entering data? Which data points did you enter? Which did you remove? Maybe these will help us help you.

Re: Statistical Bug? - not on my machine Message #11 Posted by Trent Moseley on 26 Mar 2003, 6:23 p.m., in response to message #10 by Gene Gene, See my reply to R. Lion tm

No bug -- Les got it right Message #12 Posted by Karl Schneider on 27 Mar 2003, 1:28 a.m., in response to message #1 by Trent Moseley Trent -- There is no bug. Les Bell's reply below hit the nail on the head -- not clearing the previous SDEV calculation caused it to be entered as a y-datum deleted from summation for two-variable analysis upon doing the Sigma-minus. SDEV of the y-data was undefined (sqrt of negative number). The 32Sii did not yield an error because it has separate keystrokes for x-SDEV and y-SDEV, population or sample. The 12C, 15C, and 42S will calculate both sample SDEV's with the same keystroke. The older 25C and 67 might not have two-variable stat analysis built in (I have neither unit). -- Karl

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