A water quality investigation was carried out after some cases of heavy metal poisoning were detected in a countryside village with a river running through it. The investigators were trying to establish if poisoning was worse on the north or the south of the river.
 |
North of the river |
South of the river |
Number of cases of heavy metal poisoning |
26 |
12 |
The results from a chi-squared test were:
Chi-squared value: |
5.2 |
Degrees of freedom: |
1 |
Critical values table:
Degrees of Freedom |
P = 0.05 |
P = 0.01 |
P = 0.001 |
1 |
3.83 |
6.64 |
10.83 |
2 |
5.99 |
9.21 |
13.82 |
3 |
7.82 |
11.35 |
16.27 |
What conclusions can be drawn from the information above?
The χ2 value is greater than the critical value so there is an association between heavy metal poisoning and location
The χ2 value is lower than the critical value so there is no association between heavy metal poisoning and location
Poisoning from heavy metals is worse in villages
Heavy metals are found in both locations, north and south of the river