rev HP17BII - stat problems and/or 42SX



#11

Any one out there able to provide guidance as to why I can not get the correct answer posted by the book.
For a data set 32,41, 47, 53, 54 ; the correct Std Dev 8.85

Using the 17bii I get a different answer (9+) Why the difference, did I leave something out? How do I handle frequencies?

If anyone coudl help otherwise with the 42SX for the same problem. It has been too many years since I use this HP


#12

One result is the sd for the entire population (8...), the other one for a sample from a population (9...). Refer to a statistics textbook.

hth,

Thomas

#13

Actually, the correct population standard deviation for that data set is about 8.16, not 8.85; are you sure that you're using the right numbers? As Thomas pointed out, the sample standard deviation is different, about 9.13 in this case.

Regards,
James


#14

I agree with Jame's results. The HP17bII+ manual states in Appendix B that the STDEV function calculates the sample standard deviation (divide by root(n-1)) whereas the other answer (8.16) is the population standard deviation (divide by root(n)). I am not sure where 8.85 comes from.


Edited: 11 Aug 2005, 10:03 a.m.

#15

The 8.85 is the result derived from the TI83 or TI BA II PLUS.


The reason of my question is because the class and book are offering explanation with the TI "calculators". Indeed I get the 9.12 with the HP, but if my answers is distint from the others.....
I will get an exponential grade drop !(don't want it to happen)

I do not want to go TI EITHER !!
What parameter is not being accounted for ?

The answer 8.85 ..... Sum(data) = 230 {32,41,47,53,54}
Sum x^2 = 10,972
Sum X = 30

S=1/n *(sqrroot(n(sumx^2) -(SumX)^2)

Any inputs?


#16

sorry ! Sum X = 230

#17

Jose:

There is an error in your sample set: {32,41,47,53,54} sums to 227 not 230.

I get 9.126883367 on my TI-83 Plus and TI BAII Plus using the 227 set.

Bob

#18

You can convert from one value to the other by a simple calculation:

Sdevpop=Sdevsam*SQRT((N-1)/N)

In your case, multiply the result by SQRT(4/5).

The HP11C manual shows a different approach:

Simply add the mean of the data collected so far to the data and recalculate the standard deviation.


#19

Have you made sure all your registers/memories are cleared because sum^2 should be 10639 and sum 227. Possibly drastic action but reset the calculator and try again.

Edited: 12 Aug 2005, 9:08 a.m.


#20

9.126883367 is the STD for the sample

8.163332653 is the STD for the population

The numbers above come from Excel .. another wonderful technological product, and the formulas are STDEV(range) and STDEVP(range). The difference between the two numbers is a division by SQRT(n) versus SQRT(n-1). To verify the results with your preferred HP calculator, just enter the numbers in the key Ó+, and you will all the statistical parameters of the sample and population.

Greetings,


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