Fair Tests

Types of Variables

Variables are things that vary

and change

Variables

In any experiment there are 3 variables:

An independent (changed) variable

A dependent (measured) variable

Some control variables

Let’s look at each type…

Independent Variable

This is the thing you decide to change

eg. Investigating how plants grow when they are given different amounts of water

You change the amount of water you give the plant.

So, amount of water is the independent variable.

Dependent Variable

This is the thing that changes as a result. This is the thing you measure

eg. Investigating how plants grow when they are given different amounts of water

You measure how much the plant grows. So, amount of growth is the dependent

variable.

Control Variables These are all the things that must not change to

make it a fair test. They must be kept the same.

You need to keep the plants in the same place so that they get the same amount of sunlight or shade.

You need to grow the plants in the same type of pot, that are the same size.

The plants need to have the same type and same amount of potting mix.

These are the control variables.

Summary The independent variable is changed.

Amount of water The dependent variable is measured.

Growth of plant. The control variables are kept the same.

Amount of sunlight or shade. Type of pot. Size of pot. Type of potting mix, etc.

http://www.youtube.com/watch?v=Hxbz656Euyw

Change one thing,Measure one thing (usually),

Keep everything else the same.

Time For A Joke...

A Magician was driving down the road...

then he turned into a drive way...

hahahahahahahahahah

Q. What do u call a guy with no shins?

Tony

Accuracy, Reliability and Validity

Accuracy

The exactness or precision of a measurement; relating to the degree of precision in measurement.

Highly dependant on equipment choice to measure values accurately

Reliability

• The degree with which repeated observation and/or measurements taken under identical circumstances will give the same results.

Validity

The extent to which the processes and resultant data measure what was intended.

Are the measurements you recorded caused by the variables you think.

Reliability Have I tested with repetition?

AccuracyHave I chosen equipment that will give me accurate and precise readings?

Validity

Does my experiment actually test the hypothesis that I want it to? What variables have I identified and controlled?