A level practical key terms

Validity
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Terms in this set (13)
Validity
If it measures what it is supposed to be measuring - this depends both on the method and the instruments.
True value
The value that would have been obtained in an ideal measurement - with the exception of a fundamental constant the true value is considered unknowable.
Accuracy
If measurement is judged to be close to the true value. It is a quality denoting the closeness of agreement between measurement and true value - it cannot be quantified and is influenced by random and systematic errors.
Precision
A quality denoting the closeness of agreement (consistency) between values obtained by repeated measurement - this is influenced only by random effects and can be expressed numerically by measures such as standard deviation.
Repeatability
The precision obtained when measurement results are obtained by a single operator using a single method over a short timescale
Reproducibility
The precision obtained when measurement results are obtained by different operators using different pieces of apparatus.
Uncertainty
The interval within which the true value can be considered to lie with a given level of confidence or probability. This can be estimated by considering the instruments and the method
Error
Where there is a difference between the measurement result and the true value. Can be due to both systematic and random effects
Resolution
The smallest measuring interval and the source of uncertainty in a single reading
Independent variable
A factor that you change to observe its effect on the dependent variable.
Dependent variableA factor you measure to see the effect of the independent variable.Control VariableA factor that is kept constant so that its effect on the dependent variable is consistent throughout all experiments. By controlling all factors (other than the IV and DV) you are ensuring your results are valid. Examples: Temperature - use a water bath; pH - use a buffer.ControlAn experimental condition, which allows a comparison to show any change observed, is due to the independent variable only.