Statistical Bug?  Printable Version + HP Forums (https://archived.hpcalc.org/museumforum) + Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum1.html) + Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum2.html) + Thread: Statistical Bug? (/thread30740.html) 
Statistical Bug?  Trent Moseley  03262003 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.
cC
Re: Statistical Bug?  R Lion (Spain)  03262003 I don't know if I understand you. Could you give any example?
Raul
Re: Statistical Bug?  not on my machine  Gene  03262003 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?  Trent Moseley  03262003 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
You do not get an error message on the 25C, 67, or 32SII but see the answer: 4.24
Re: Statistical Bug?  not on my machine  Trent Moseley  03262003 Gene, See my reply to R. Lion
tm
Re: Statistical Bug?  R Lion (Spain)  03262003 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  R Lion (Spain)  03262003 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: Statistical Bug?  Les Bell  03262003 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 sigmaminussed, or clear the stack, it will work just fine. Best,
 Les [http://www.lesbell.com.au]
Re: Better solution  Trent Moseley  03262003 Raul Lion, I don't bother. I use one of the machines that don't have the problem.
tm
Re: Better solution  R Lion (Spain)  03262003 Oh well... then send me your 15c and I'll send you a new 32sII ;)
Raul
Re: Better solution  Trent Moseley  03262003 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
No bug  Les got it right  Karl Schneider  03272003 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 ydatum deleted from summation for twovariable analysis upon doing the Sigmaminus. SDEV of the ydata was undefined (sqrt of negative number). The 32Sii did not yield an error because it has separate keystrokes for xSDEV and ySDEV, 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 twovariable stat analysis built in (I have neither unit).
 Karl
