1. Dr. Amjad El-Shanti MD, PMH,Dr PH University of Palestine 2016
Chi-Square test
Dr. Amjad El-Shanti
MD, PMH,Dr PH
University of Palestine
2016

2. Chi square test
Used to measure the association between two qualitative variables.
Example: *the association between miscarriage and exposure for pesticide.
*the association between vaccination and Influenza.
*the association between hypertension and smoking

3. Questions
Is there relation or association between miscarriage and pesticide exposure?
Is there relation or association between vaccination and Influenza?
Is there relation or association between hypertension and smoking?

4. Hypothesis
Null Hypothesis: There is no statistically significant correlation between miscarriage and pesticide exposure.
Alternative Hypothesis: There is statistically significant correlation between miscarriage and pesticide exposure.

5. Steps for Hypothesis testing
Construct observed table.
Construct Expected table.
E= C t * R t /Grand total
3.Calculate chi square (X2).
X2 = Σ ( {O-E}2/ E).
4. d.f. = (C-1)*(R-1).
P value (d.f., X2(.
6. Compare p value with significant level (α).

6. Example:
If the sample is composed of 200 women 100 of them from village and exposed to pesticide. 30 women of village women had miscarriage while 10 of the city had miscarriage. Is there association between the pesticide exposure and miscarriage?

7. 1.,2. Construct observed and expected table.
Total
Not-exposed
Exposed
Observed 40 10 30
Miscarriage
160 90 70
No Miscarriage
200
100
E= C t * R t /Grand total
Total
Not-exposed
Exposed
Expected 40
40*100 /200
(20)
40*100 / 200
Miscarriage
160
160*100/200
(80)
No Miscarriage
200
100

8. 3. Calculate chi square (X2).
X2 = Σ ( {O-E}2/ E).
X2 = ({30-20}2 /20) + ({10-20}2 /20)+ ({70-80}2 /80)+ ({90-80}2 /80)
= 100/ / / /80
= = 12.5

9. Degree of freedom and compare p value with significant level
4. d.f. = (C-1)*(R-1).
= (2-1) * (2-1).
= 1 * 1= 1
p >
p >α
P value significant reject null hypothesis
There is statistically significant association between pesticide exposure and miscarriage.