Learning focus
Develop safe and reproducible practical methods, record precise observations and measurements, process evidence and evaluate experimental quality.
Accuracy
Accuracy describes closeness to the accepted or true value. It can be improved by calibration, avoiding systematic error and choosing a method that actually measures the intended quantity.
Precision
Precision describes the closeness of repeated readings and the detail permitted by scale resolution. A precise set can still be inaccurate if every reading is shifted by the same calibration error.
Reliability
Reliable results are reproducible under the same conditions. Repeats, sufficient sample size and consistent technique improve reliability. A mean reduces the effect of random variation.
Validity
A valid investigation answers the stated question. Control variables, a suitable range, a correct control and an appropriate measurement make a fair test. Many marks use the language of fair testing even when the word validity is not printed.
Practical or data skill
Classify example problems as accuracy, precision, reliability or validity issues and explain the distinction.
Examination tip
Avoid using “accurate” to mean simply “careful” or “repeatable”.
Review questions and suggested answers
Question 1
Can precise results be inaccurate?
Suggested answer
Yes, if a systematic error shifts all readings.
Question 2
How do repeats improve reliability?
Suggested answer
They reveal variation and allow a mean.
Question 3
What makes a fair test valid?
Suggested answer
Only the independent variable changes while relevant variables are controlled.
