Year 8 Science · Unit 4 · Lesson 8

Accuracy, Precision and Reliability

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Learning Goals

Compare accuracy, precision, reliability and validity using definitions, error types and improvement strategies.
Apply the distinction between systematic and random error to a real measurement scenario.
Explain why repeating measurements with faulty equipment does not improve accuracy.

Warm Up

Compare two

Complete the table to compare four key measurement concepts. Use lesson content to fill each cell.

Concept	Definition (in your own words)	What type of error affects it?	How to improve it
Accuracy
Precision
Reliability
Validity

Your Turn

Scenario

A student is measuring the length of a 10.0 cm rod. Their ruler has a worn-off zero mark — the scale begins at 0.3 cm, but the student does not notice and reads the ruler as if it starts at zero. The student measures the rod five times and records: 10.3 cm, 10.2 cm, 10.3 cm, 10.4 cm, 10.3 cm.

(a) Are the student's results precise? Justify your answer using the values in the scenario.

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(b) Are the student's results accurate? Justify your answer by comparing the mean to the true value.

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(c) What type of error is affecting the student's results — random or systematic? Explain what causes this type of error and name a feature from the scenario that identifies it.

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(d) If the student repeats the measurement 10 more times with the same ruler, would accuracy improve? Explain why or why not.

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Wrap Up

In one sentence, what was the main idea of this lesson?