For two medical diseases a and

b, it is known that the percentage of people in the general population who suffer from a only is 20%, the percentage of those who suffer from b only is 12%, while the percentage of people suffering from both diseases is 4%. Are the occurrences of the two diseases independent? If not, what is the percentage increase or decrease of the probability that someone suffers from a once it becomes known that he/she suffers also from b?