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CHITEST gives unexpected value

asked 2019-11-23 20:11:03 +0100

telmo_trooper gravatar image

updated 2020-07-30 00:26:14 +0100

Alex Kemp gravatar image

I have two columns denoting respectively observed and expected frequency, I then calculate (chi-square) for each row with ((OBSERVED-EXPECTED)^2)/EXPECTED) and proceed to SUM all rows to get the actual value. The resulting value is different from the value given by CHITEST and I can't seem to understand why (in fact, I can't really find much documentation about this function at all). Also, the values in my table are rounded for display.

Observed    Expected  X²
3           4.0       0.26
15          18.5      0.66
47          42.5      0.47
76          65.2      1.78
68          75.0      0.66
74          69.0      0.36
46          52.9      0.90
39          34.8      0.52
15          20.0      1.25
9           10.2      0.15
5           4.7       0.02
2           2.0       0.00
0           0.8       0.75
1           0.3       2.02

SUM: 9.782  CHITEST: 0.712

Here's my table (in case it's useful): Exemplo_Qui-Quadrado.ods

Could someone explain to me how is the value of CHITEST calculated?

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answered 2019-11-24 08:44:08 +0100

updated 2019-11-24 09:05:00 +0100

The function CHITEST is implemented in ScInterpreter::ScChiTest. In your spreadsheet, given the χ² (result of image description) in E17, the function is equal to

=CHIDIST(E17;13)

where 13 is degrees of freedom: number of rows of a test series (14) decremented by 1 and multiplied by number of columns (1).

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Thank you!

telmo_trooper gravatar imagetelmo_trooper ( 2019-11-24 19:10:04 +0100 )edit
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Asked: 2019-11-23 20:11:03 +0100

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Last updated: Nov 24 '19