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AQA Science: Glossary - Validity
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Data is only valid for use in coming to a conclusion if the measurements taken are affected by a single independent variable only. Data is not valid if for example a fair test is not carried out or there is observer bias.
For example: In an investigation to find the effect on the rate of a reaction when the concentration of the acid is changed, it is important that concentration is the only independent variable. If, during the investigation, the temperature also increased as you increased the concentration, this would also have an effect on your results and the data would no longer be valid.
e.g. Valerie and Vernon are investigating how the length of a cylinder of putty effects its electrical resistance. However, to make the putty a different length they roll it out more thinly! This means that the putty's length increases, but in addition they alter the cross-sectional area of the putty. This last factor also affects the resistance, so they have not carried out a fair test.
- Briefly outline what Valerie and Vernon should have done to make their data valid.
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