Correlating rick factors

• In the 1930s rates of lung cancer began to increase sharply and scientists could not explain this.
• Scientists looked very closely at people's lifestyle habits to see if they could link any of these with lung cancer.
• Studying the patterns of disease to determine risk factors is called epidemiology.
• Scientists noticed that lung cancer is much more common among cigarette smokers than among non-smokers.
• Scientists looked at how many cigarettes people smoked each day and then how many of these people developed lung cancer.
• Scientists were looking to see if there was a correlation between lung cancer and smoking.
• As the number of cigarettes smoking per day increases, the risk of developing lung cancer also increases. This is a positive correlation.

  
• Scientists began to look at how cigarette smoking could cause cancer. They discovered that cigarette smoking contains chemicals which damage DNA and increases the rick of cancer. They are called carcinogens.
• We cannot draw conclusions from a small or non-random sample.