1. FAIR TESTS

2. What is a fair test?
An investigation where only one factor is changed while all others are kept the same (controlled).
This way, the changes are due only to the thing we want to test
e.g. if testing the effect of amount of light on growth of seedlings, keep everything else the same e.g. type of soil, amount of water, temperature, length of time grown etc.

3. Variables
The things that can change in an experiment are called variables.
e.g. in the seedling experiment, variables were amount of light, amount of water, temp, soil type….

4. There are different types of variables in an investigation:
Independent variable: the thing that is changed on purpose
Dependent variable: the thing that is measured
Controlled variables: all other changeable factors that must be kept the same to ensure a fair test

5. Independent Variable (What I change)
Question
Independent Variable (What I change)
Dependent Variables (What I observe)
Controlled Variables (What I keep the same)
How much water flows through a tap at different openings?
Tap opening (closed, half open, fully open)
Amount of water flowing measured in litres per minute
- tap
- water pressure, or how much the water is "pushing"
Does heating a cup of water allow it to dissolve more sugar?
Temperature of the water measured in degrees Centigrade
Amount of sugar that dissolves completely measured in grams
- stirring
- type of sugar
Does fertilizer make a plant grow bigger?
Amount of fertilizer measured in grams
Growth of the plant measured by its height
AND / OR
Growth of the plant measured by the number of leaves
Same size pot for each plant
Same type of plant in each pot
Same type and amount of soil in each pot
Same amount of water and light
Make measurements of growth for each plant at the same time

6. Reliability
How consistent (or similar) the results of a test are when repeated under identical conditions
Precise

7. Validity How well a test measures what it is supposed to be measuring
Accuracy

8. An example to show the difference between reliability and validity:
Bathroom scales…
An example to show the difference between reliability and validity:
You weigh 55 kg. You test your bathroom scales by standing on them 10 times.
If they read 55 kg each time, the test is valid (accurate) and reliable (consistent)
If they read ’45 kg’ each time, the measurement is reliable (consistent) but not valid (accurate)
If they read close to 55 kg each time, but not exactly e.g. 54, 56, 55, 56, 56, 54…, the test is valid (accurate), but not reliable (consistent)