Can environmental factors affect the incidence of schizophrenia? A recent project measured the incidence of the disease among children born in a region of eastern China: 192 of 13,748 babies born in the midst of a severe famine in the region in 1960 later developed schizophrenia. This compared with 483 schizophrenics out of 59,088 births in 1956, before the famine, and 695 out of 83,536 births in 1965, after the famine (St. Clair et al. 2005).

a. What two variables are compared in this example?

b. Are the variables numerical or categorical? If numerical, are they continuous or discrete; if categorical, are they nominal or ordinal?

c. Effectively display the findings in a table. What kind of table did you use?

d. In each of the three years, calculate the relative frequency (proportion) of children born who later developed schizophrenia. Plot these proportions in a line graph. What pattern is revealed?