Calculating Standard Deviation Homework

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Homework Help Overview

The discussion revolves around calculating the standard deviation of a dataset. Participants are examining the original poster's calculations and the methodology behind determining standard deviation, including the choice of divisor (n or n-1) for the calculation.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster presents a series of calculations and questions whether any errors were made. Some participants point out potential errors in the calculations and question the clarity of the data presented. Others inquire about the appropriate divisor for calculating standard deviation.

Discussion Status

Participants are actively engaging with the original poster's calculations, offering feedback on potential errors and clarifying the method for calculating standard deviation. There is a mix of interpretations regarding the data structure and calculations, with no explicit consensus reached.

Contextual Notes

There is confusion regarding the format of the data presented by the original poster, with questions about whether it consists of one list or two separate lists. This ambiguity may affect the calculations and interpretations being discussed.

EdmureTully
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Homework Statement



I have to calculate the standard deviation

Homework Equations



http://0.tqn.com/d/statistics/1/0/M/-/-/-/standarddev.GIF

The Attempt at a Solution



0.64 0.4096
2.06 4.2436
0.16 0.0256
3.24 10.4976
1.74 3.0276
1.06 1.1236
4.04 16.3216
1.56 2.4336
1.3 1.69
3.64 13.2496
3.16 9.9856
3.04 9.2416
0.86 0.7396
3.56 12.6736
2.94 8.6436
1.74 3.0276
2.96 8.7616
2.34 5.4756
6.46 41.7316
2.76 7.6176

total = 151.9204

uncorrected sd = 2.75
corrected sd = 2.83

1 89.20
2 86.50 2.70
3 88.40 1.90
4 91.80 3.40
5 90.30 1.50
6 87.50 2.80
7 92.60 5.10
8 87.00 5.60
9 89.80 2.80
10 92.20 2.40
11 85.40 6.80
12 91.60 6.20
13 87.70 3.90
14 85.00 2.70
15 91.50 6.50
16 90.30 1.20
17 85.60 4.70
18 90.90 5.30
19 82.10 8.80
20 85.80 3.70

the answer they get is 2.91

average is 88.56

did i make any calculation error?

I can't believe i made any calculation error
 
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Yes, you made some errors. Your value for the mean is correct. One of your differences is off, and you compounded that error by not summing the squares accurately.

It would have helped if you described what you were doing instead of just posting arrays of unlabeled numbers and leaving it to others to decipher what you did.
 
Ok, thanks. One last thing, do I have to divide by n-1 or just n?
 
For an unbiased estimator, you need to divide by n-1.
 
EdmureTully said:

Homework Statement



I have to calculate the standard deviation

Homework Equations



http://0.tqn.com/d/statistics/1/0/M/-/-/-/standarddev.GIF

The Attempt at a Solution



0.64 0.4096
2.06 4.2436
0.16 0.0256
3.24 10.4976
1.74 3.0276
1.06 1.1236
4.04 16.3216
1.56 2.4336
1.3 1.69
3.64 13.2496
3.16 9.9856
3.04 9.2416
0.86 0.7396
3.56 12.6736
2.94 8.6436
1.74 3.0276
2.96 8.7616
2.34 5.4756
6.46 41.7316
2.76 7.6176

total = 151.9204

uncorrected sd = 2.75
corrected sd = 2.83

1 89.20
2 86.50 2.70
3 88.40 1.90
4 91.80 3.40
5 90.30 1.50
6 87.50 2.80
7 92.60 5.10
8 87.00 5.60
9 89.80 2.80
10 92.20 2.40
11 85.40 6.80
12 91.60 6.20
13 87.70 3.90
14 85.00 2.70
15 91.50 6.50
16 90.30 1.20
17 85.60 4.70
18 90.90 5.30
19 82.10 8.80
20 85.80 3.70

the answer they get is 2.91

average is 88.56

did i make any calculation error?

I can't believe i made any calculation error

What on Earth is your data? Is the first data set a list of 40 numbers (presented as two lists of 20, or is it two separate lists, each of size 20? If it is a single list of size 40 I get a total of 210.1804; if it is two lists of size 20 each I get a total of 49.26 for the first list and a total of 160.92094 for the second list. None of these match what you claim---but your analysis is totally meaningless because you do not give any clues as to what you are doing.