Measurement, repeats and reliability
Data is only as good as the way it was collected. Knowing the difference between a mistake, a random error and a systematic error is what lets you improve a method.
Part of your national curriculum
- Working scientifically: Make and record observations and measurements using a range of methods, and evaluate the reliability of methods
Lesson overview
What you'll learn in this lesson
Make and record observations and measurements using a range of methods, and evaluate the reliability of methods
Key learning points
- • Choosing instruments and resolution
- • Random and systematic error
- • Repeats, means and anomalies
- • Accuracy, precision and reliability
This lesson at a glance
- 28 minutes
- 20 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 20
Visual introductionPicture this
Measurement, repeats and reliability
Data is only as good as the way it was collected. Knowing the difference between a mistake, a random error and a systematic error is what lets you improve a method.
In a nutshell
Make and record observations and measurements using a range of methods, and evaluate the reliability of methods
Learning cycle
Part 2 of 20
Learning cycle 1 of 2
Part 1 · Choosing instruments and resolution
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 20
Learn
Choosing instruments and resolution
Resolution is the smallest change an instrument can detect. A balance reading to 0.01 g has higher resolution than one reading to 1 g, and measuring 2.4 g on the coarser balance is meaningless. Match the instrument's resolution to the size of the quantity you are measuring.
Reset break
Part 4 of 20
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 20
Learn
Random and systematic error
Random errors scatter results either side of the true value and are reduced by repeating and taking a mean. Systematic errors shift every reading the same way, for example a balance not zeroed, and repeating does not help: only checking and calibrating the equipment will.
Quick check
Part 6 of 20
Quick check
Part 7 of 20
Reset break
Part 8 of 20
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 20
Learning cycle 2 of 2
Part 2 · Repeats, means and anomalies
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 20
Learn
Repeats, means and anomalies
Three repeats at each value allow a mean and reveal anomalies, which are results far from the others. Identify an anomaly, exclude it from the mean, and say why it may have occurred, such as a bubble on the thermometer or a mistimed stopwatch. Never quietly delete it.
Explore the idea
Part 11 of 20
Learn
Accuracy, precision and reliability
Accurate results are close to the true value; precise results are close to each other. Data can be precise but consistently wrong if there is a systematic error. Reliable results are ones that are reproduced when the method is repeated, ideally by someone else following the same written method.
Reset break
Part 12 of 20
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 20
Quick check
Part 14 of 20
Explore the idea
Part 15 of 20
Worked example
Worked answer: results at one temperature are 32 s, 34 s and 51 s. Explain how to handle these (3 marks)
The 51 s reading is an anomaly, because it is far from the other two which agree closely (1). It should be excluded from the mean, giving (32 + 34) ÷ 2 = 33 s (1). A likely cause is a delayed stopwatch start or a misjudged endpoint, and the measurement should be repeated to confirm the value rather than simply discarded without comment (1).
Reset break
Part 16 of 20
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 20
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 18 of 20
Game · Recall cards
What does repeating an experiment and averaging help reduce?
Card 1 of 4
Mastery quiz
Part 19 of 20
Marked quiz
End of lesson quiz: Measurement, repeats and reliability
4 questions, marked with the reasoning shown. No timer.
1. What does repeating an experiment and averaging help reduce?
2. An anomalous result is one that is:
3. A method is reliable if:
4. Random error is reduced by
Lesson round-up
Part 20 of 20
Lesson round-up
Ready when you are
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Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 20 · Watch & discover
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Make and record observations and measurements using a range of methods, and evaluate the reliability of methods