How would you calculate the Standard Deviation for grouped data on the GDC?

[y.v]

I know how to calculate the Standard Deviation and Variance of Grouped data by hand.

However, is there any way to calculate those using 1-Variable Stats on the GDC?

[Vvi]

Yes for standard deviation (both sample and population), no for variance. At the same time the calculator will also calculate mean, minimum, lower quartile, upper quartile, median and maximum. You need to be able to do this for your exam.

You go to Lists on the calculator (press STAT), then enter when the word 1: EDIT in the EDIT section is highlighted. From there, you fill in the lists with information from each column.

Then press STAT again and this time, don't press EDIT but press the right arrow so the CALC heading is highlighted. Pressenetr for 1-Var Stats, then press "2nd 1" or whatever lists you have entered your information in (the list name comes up as L1, L2, etc. up to 6, and they are marked in yellow over the keys 1 to 6).

Press enter, and you have a bunch of information. The first x with the bar over it is the mean, the next one is the sum of all the values. Sx is the sample standard deviation, and sigma x (the weird circle one) is the population standard deviation. To get variance on the calculator, you have to square these standard deviations.

If you scroll down the screen with the arrow button, you will see the minimum, lower quartile, median, upper quartiler and maximum values for your data. Very sueful so you don't waste time doing these by hand.

You also need to know how to use 2- Var Stats (which is the same, but for calculations using 2 variables, X and Y).

[moneyfaery]

For grouped data, the value of the random variable 'X' is the average of the group 'range'. Just keep that in mind when entering values for X and freq.

Vvi gave a wonderful explanation though.

[y.v]

Thanks Vvi/Irene for answering

However, have a look at this example of a question with grouped data:

In a class of 10 students,

(Refer to attachment)

Now, in this case, I would put in IB Score in L1 and Frequency in L2.

However, while calculating 1 Variable Stats, which column would I use?

P.S.: Vvi, do you need to know 2 Variable Stats for SL?

Edited May 2, 2009 by y.v

[moneyfaery]

1-Var Stats [Xlistname,freqlist] is how you would enter the command on the GDC, so enter 'Test Score' for L1 and 'Freq' for L2. It doesn't matter really as long as you correctly specify which is which with the command:

1-Var Stats L1, L2

2-Var Stats isn't that useful for Methods SL/HL.

Edited May 2, 2009 by Irene

[Vvi]

I thought you were a Studies student (in which case you'd need to know 2- Var Stats). No you don't need it for SL.

For questions with frequency, you use 1- Var Stats and enter score in L1 and the frequency in L2. Then use 1- Var Stats to calculate the answer. Don't use 2- Var Stats, as then the calculator thinks that L1= x variable and L2= y variables.

And you need that comma in between the lists (which is above in Irene's post).

[y.v]

That makes perfect sense.

Thanks, again