At an initial examination in oxford, massachusetts, migraine headache was found in 5 of 1,000 men aged 30 to 35 years and 10 in 1,000 women aged 30 to 35 years. the inference that women have a two times greater risk of developing migraine headache than do men in this age is:
a) incorrect, because a ratio has been used to compare male and female rates
b) incorrect, because of failure to recognize the effect of age in the two groups
c) incorrect, because no data for a comparison (control) group are given
d) incorrect, because of failure to distinguish between incidence and prevalence