The Fair Test What does “fair testing” mean? A fair test is one where only one variable is changed, while all other variables are controlled (kept the same) Today’s aims: • Recognise the importance of controlling variables • Identify variables that need to be controlled • Identify flaws in an experiment due to variables that are not controlled Controlling variables is important In the next few slides, identify what is not being controlled, and how it should be controlled so that the experiment produces more meaningful and reliable results. The hug survey People are stopped randomly in the street and asked if they would like a hug. The results show that 17% of people will accept a hug from a stranger when asked. Dan’s van Dan is a man with a van. During a job delivering 21 bags of cement, he decides to find out what his van’s fuel consumption is. He makes a note of the distance travelled and how much fuel was used. He concludes his van achieves 21 km per liter of gas. Red or green Tesco wants to see whether its customers prefer red grapes to green grapes. Each customer is shown one of each colour when they enter the store, but they are told they can only take one grape. Sweet enough Maggie wants to know what type of sugar takes longest to dissolve. The three types are: brown, white and demerara. She puts 25g of each type in 100cm3 of water and times how long they take to dissolve completely. She uses an automatic stirrer. A stirrer The “chill pill” A company is testing a relaxation pill. They get hundreds of men and women of different ages, races and backgrounds (as random as possible) to do the test. They make them do something stressful first, then immediately afterwards give them a pill. Afterwards they measure how much they had relaxed after taking the pill. Note: Assume the method for measuring “relaxation” is accurate.