You need to use the class midpoints - not the (class) upper boundary values.
I have a frequency table showing age distribition in Auckland supercity election 2010 and I have in the coloumns I have Age, frequency, percentage, upperbondary, class midpoint, class width, histogram height.
In my age rows I have things such as 20 to under 40, 40 to under 50, 50 to under 60, 60 to under 70, and 70 to under 80.
Now my question is how do I find the mean age and standard deviation age from that frequency table.
I have casio fx-82MS calculator and I switched to sd mode and cleared the memory and I enter the data from upper boundary and I press the M+ button after i enter each of these data's and once I finish I press shift 2(s-var) then select the mean and stadard deviation. But the answer I get is wrong. Can anyone tell me what I'm doing wrong????
You need to use the class midpoints - not the (class) upper boundary values.
I tried entering it from class midpoint but I still get wrong answer. I get 54 for mean and 15.2 for standard deviation. Here is my raw data for class midpoint: 30, 45, 55, 65, 75. The answer is 58.63 years for mean and 14.89 years for standard deviation. But my question here is, how do we get them?
You should start with the mean. You have given the 5 midpoints. Now, what are the 5 class frequencies?
How do you 'know' what the answer is? Is it reported along with the table or something? You most likely won't be able to get the exact same answer because when the data gets binned you lose quite a bit of information.
Quick example:
Real data: -0.9, .1
mean of actual data = -.4
Which corresponds to the following binned Data:
(-1, 0]: 1
(0, 1] : 1
Mean calculated using binned data: 0
These don't match up but we shouldn't expect that they could possibly perfectly match up.
The frequencies are in order: 30, 20, 48, 56, 58
Okay, so then it is straight-forward to compute the mean:
(30)*(30) + (20)*(45) + (48)*(55) + (56)*(65) + (58)*(75) = 12430
Thus, the mean is:
12430/212 = 58.6321
Do you follow?
thanks it worked but the problem is how do i enter them to calculator? thats the problem, when finding standard deviation.
In my calculator I have to go on sd mode and enter those data's then press M+ and then compute the mean and standard deviation but it doesnt work. I tried putting numbers like this 30;30 and press M+, 20;45 and press M+ and such and to compute the standard deviation and mean age but still didnt work.
For calculator issues, just google it for you
http://www.ehow.com/how_7484887_casi...tructions.html
www.usq.edu.au/resources/fx82ms.pdf
And here is the picture of frequency table with answer below the tables. I really need help on this.
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