Scenario: Dr Smith wants to test whether a new therapy programme reduces cigarette smoking. Dr Smith selected a sample of heavy smokers (20 or more cigarettes per day) to participate in his study. Dr Smith first measured exactly how many cigarettes each participant smoked per day. All participants then took part in the new therapy programme. After 2 months, Dr Smith again measured how many cigarettes each participant smoked per day. From this, Dr Smith observed that participants smoked 30% fewer cigarettes per day after participating in the therapy. Dr Smith concludes that the new therapy programme is an effective tool in curbing smoking behaviours