FAIR TESTS

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.

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….

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

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

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

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

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)