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Correlation

A relationship between two variables.

Correlation is an association and does not imply causation (which exists if the independent variable is known to change the values of the dependent variable)

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Positive correlation

Exists when an increase in one variable is accompanied by an increase in the other variable

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Negative correlation

Exists when an increase in one variable is accompanied by a decrease in the other variable

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Correlation

Strength of correlation is proportional to spread of values from line of best fit.

Strong positive correlation

Weak negative correlation

No correlation

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Qualitative versus Quantitative data

Qualitative

The values collected do not imply a numerical order or range of effect.

e.g. the iodine solution test for starch is an example of the generation of qualitative data: starch either is present or it is not present.

What type of graph would be used to show this?

Quantitative

The values collected indicate a numerical value, e.g. 10cm³ of O₂ is produce per minute with 0.1% catalase whereas 1cm³ is liberated per minute with 0.01% catalase.