Lung cancer is the most common cause of cancer death in the United States and throughout the world. Not all lung cancer is smoke related, however there is a direct correlation between the quantity you smoke and the occurrence of lung cancer. The Surgeon General's report on the consequences of smoking, reported in 1982, shows this correlation. Thus to assess the risk of lung cancer for a smoker, physician calculate a pack year history. A pack year history is essentially the magnitude of primary smoke exposure.
Determine the number of packs of cigarettes a person smokes per day.
Determine the number of total years the person has smoked.
Multiply the number of packs per day by the number of years they've smoked.
For example, if John Doe has smoked two packs per day for 30 years, his pack year history would be 60 pack years.