# The Fair Test

```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
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.
```