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College of Veterinary Medicine

 

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  Excercise › Disease in Diary Herd

 
 

Statistical Test for Association

 

Chi Square Test for Assocation (Hypothesis Testing)

H0 (Null Hypothesis)....... There is no association between eating the specific feed/food item and coming down with the disease.

H1 (Alternate Hypothesis)...... There is an association.

Level of Significance (alpha)..... 0.05 or 5%

Degrees of Freedom..... (r-1)*(c-1) (2-1)*(2-1)=1

Test Statistic

Chi Sq. calculation:   chiaquare

Decision:

Compare Chi Sq. calculated with Chi Sq. tabulated.

Chi Sq. tabulated = 3.84

Chi Sq. calc from test statistic

If:

Chi Sq. calc. < Chi Sq. tabulated Accept H0

Chi Sq. calc. >> Chi Sq. tabulated Reject H0, Accept H1

The 2 by 2 Table

Chi Square Test for Association

D+
D-
Total
F+
a
b
a+b
F-
c
d
c+d
Total
a+c
b+d
n=(a+b+c)

Chi Square Test for Mink Outbreak

D+
D-
Total
F+
1956
2731
4867
F-
2
218
220
Total
1958
2949
4907

Enter data for cells

a
b
c
d
1956
2731
2
218

Numerator = 8.695E+14

Denominator = 5.9539E+12

Chi Sq.(cal) = 146.037281

Chi Sq. (tab) = 3.84

Chi Square Values for all feeds

Feed Item
Attribute Risk
Relative Risk
Chi Square Calc.
Fish
1
1
1
Protein
1
1
1
Red meat
-1
1
1
Liver
41
42
146
Cereals
-2
1
3
Blood/Bone meal
1
1
1
Horse fat
1
1
1
Fish fat
0
1
1
Vegetable fat
0
1
1
Vitamins/Minerals
1
1
1

 

   

  

 

 

 

 

 

 
 

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