Fair Testing

FAIR TESTING is the investigation approach that finds relationships between factors (VARIABLES). A single variable is changed (called the INDEPENDENT VARIABLE), and another variable is measured (called the DEPENDENT VARIABLE). Meanwhile, other variables must be kept the same (called CONTROL VARIABLE). This is so that the results can be used to make comparisons, and any differences are said to be the result of the changed / independent variable. 

For example, if a capful of one washing powder cleans a load of clothes, how do we know whether it is better or worse than other washing powders?

The key to fair testing is: keep as many of the things that can vary, the same for each test. 

This would determine which powder cleaned best for the same amount used. However, it would not take price into account. A product which is 'not as good' could be cheaper than a 'better' one. So, in another sense the cheaper product could still be best. 

Experiments often include seeing the effect of a change. To do a fair test, you need to set up: 

• one experiment in normal conditions called a control

• one or more experiments with one factor changed in each. 

When testing washing powders, the control could be a wash with no washing powder to compare with the other results. 

Careful planning is required to ensure a fair test is carried out and the results are valid. The steps required when planning an investigation include:

Knowing what you are trying to find out

An aim gives the purpose of the investigation. It is very important that you know exactly what you are trying to find out. A hypothesis is a testable prediction or educated guess as to the outcome, and is based on what you already know. 

Making sure it is a fair test

Knowing what all the variables are and controlling them (where possible) is important if observations and measurements are to be accurate and valid. 

• The independent variable is the one you change deliberately to see the effect it has, e.g. the force used to push the trolley. 

• The dependent variable is what you measure or observe and depends on the independent variable, e.g. the time the trolley takes to travel 1 metre (from this you can then calculate the trolley's speed). Any other variables that may affect the results need to be kept the same, e.g. the trolley used, the surface it is pushed on, the distance over which it is timed, how the trolley is pushed, what is used to time the journey. 

• A control is often used in biological investigations. The control differs from the experimental part of the investigation in only one way and that is the variable being tested. The control and experiment are compared to each other, e.g. starch testing leaves from a plant growing in the sun (control) and one grown in the dark (experiment). 

Using the correct equipment

Make a list of everything needed to carry out the investigation. Know how to use all the equipment correctly and how to collect data accurately. 

Have a clear easy-to-follow method

Write a method as a series of short steps that follow a logical order so another person could follow them and get the same results as you did. Underline key words to draw attention to important instructions. Include labelled diagrams if they help clarify what to do. You could do a trial run, to pick up any glitches and make corrections before the actual investigation.