1.On an effort to evaluate the health effects if air pollution containing Sulphur, 90 individuals living near a pulp mill in Finland were questioned about various symptoms following a strong emission released in September 1987.The same 90 subjects were questioned again 4 months later during a low exposure period.Of the 20 individuals who had experienced headaches during the high exposure period, 4 also had headaches during the low exposure period and 16 did not.Of the 70 subjects who did not have a headache during the high exposure period, 4 experienced headaches during the low exposure period and 66 did not.At the 0.05 level of significance, test the null hypothesis that there is no association between exposure to air pollutants containing Sulphur and the occurrence of headaches.What do you conclude?