Accuracy, Precision, Errors & Reliability
Key experimental-design vocabulary examiners reward, from accuracy and precision to validity and resolution.
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Questions Covered in This Set
12 cards to master
Accuracy
How close a measurement is to the true (accepted) value.
Precision
How close repeated measurements are to each other — it says nothing about being correct.
Random error
An error that varies unpredictably in size and direction (e.g. reaction time on a stopwatch). It reduces precision; fix by repeating and taking a mean, or using finer-resolution instruments.
Systematic error
An error that shifts every reading by the same amount or direction (e.g. zero error, heat loss). It reduces accuracy and repeating does NOT help; fix by calibrating/zeroing or changing technique.
Zero error
A type of systematic error where an instrument does not read zero when it should (e.g. a balance showing 0.5 g when empty).
Anomalous result (outlier)
A single reading that clearly doesn't fit the pattern. Exam answer: identify it, repeat that measurement, and exclude it from the mean.
Repeatable vs reproducible
Repeatable = the same person, same method and equipment gets closely agreeing results. Reproducible = a different person or different apparatus gets the same result.
Reliable
Trustworthy overall — both repeatable and reproducible; achieved through repeats and consistency.
Valid
The experiment actually answers the question asked: a fair test where only the independent variable changes and other variables are controlled.
A student's results are precise but not accurate — why, and how to fix?
A systematic error (e.g. an uncalibrated thermometer reading +3 °C) shifts every result. Fix by calibrating or replacing the instrument — repeating will not help.
Resolution
The smallest change in a quantity an instrument can detect/display; finer resolution gives more precise measurements.
Confounding variable
An uncontrolled variable that changes alongside the independent variable (e.g. lamp warming a plant), making results invalid even if precise.
