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How Science Works

Links between Variables - Causal - Association - Chance.

Scientists look at how changing one variable affects another variable.

If a change in the independent variable alone causes a
change in a dependent variable then the link is said to be causal.
Causal means that a change in one variable
causes a change in another variable.
For example changing the velocity of a car changes its braking distance.
Scientists try to identify causal links as these give the clearest information
and can lead to a fair test.

If a change in the independent variable and a change
in another variable are both linked by a change in a third variable
then the link is said to be due to association.
Association means that the changes are associated with each other.
For example, the rate of growth of a crop can be affected by soil acidity.
The amount of fertiliser used on the crop will affect
both the rate of growth and the soil acidity.
The information from links due to association is less clear
and therefore less useful than the information from causal links.

If a change in the independent variable and a change
in another variable are not related at all
then the link is said to be due to chance occurrence.
Chance occurrence means that the two variables just happen
to change in that way but one variable has no effect on the other.
For example, the number of emails being sent
and the number of cars being driven on the road
have both increased in the last twenty years.
The information from links due to chance occurrence is not valid.

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