Estimating backwards

The smoking rate among women in South Korea is likely to be nearly triple the official figure of 6.4 percent, due to under-reporting, according to a story in The Korea Bizwire quoting a health expert.
In 2016, smoking rates in South Korea were ‘measured’ at 40.7 percent for men and 6.4 percent for women.
But Jeong Geum-ji of Yonsei University’s graduate school of public health said the difference in the incidence of lung cancer among men and women was narrower than that in respect of the smoking rate. In 2015, for example, 17,015 men and 7,252 women were newly diagnosed with lung cancer; so 2.4 times more men than women.
“If the smoking rate for men is 6.4 times higher than that for women, then it would be reasonable for the lung cancer incidence rate to also be 6.4 times higher,” Jeong was quoted as saying in a report submitted to a parliamentary forum. “However, the difference stopped at 2.4 times.”
The report said that, on the assumption that there were no genetic conditions at play in the occurrence of lung cancer, given the incidence rate, the smoking rate for women was probably more like 17.3 percent.