3. Minor Technique Variation
3.1. Examples
Small variations in how firmly a stopper is pushed into a flask between trials, affecting gas pressure readings slightly
Inconsistent stirring speed or duration when dissolving a substance, causing slight variation in the concentration achieved each trial
Small differences in the position of electrodes between trials in an electrochemistry experiment, affecting resistance readings
Slight variation in the time taken to transfer a sample between containers, introducing small temperature differences between trials
Minor differences in how a pipette is held or released, causing small variation in the volume delivered each trial
Minor Technique Variation: A Four-Step Analysis
Use the four-step framework to analyse minor technique variation:
- Step 1 — Identify the source
Observation / procedure — small, unavoidable differences in how the procedure is carried out between trials, not a single one-off mistake. The variation is inherent in manual technique and cannot be completely eliminated.
- Step 2 — Classify the behaviour
Unpredictable spread → Random error → affects precision. The direction and magnitude of the variation differs between trials, so results scatter around the true value rather than being consistently displaced in one direction.
- Step 3 — Explain the impact
Results are scattered above and below the true value. No single trial is consistently too high or too low — the variation averages out over many measurements. Accuracy is not affected, but precision is reduced, and the effect is more pronounced when sample sizes are small.
- Step 4 — Suggest an improvement
Minor technique variation is reduced, not eliminated — standardise the procedure as tightly as possible and repeat measurements to average out the random spread.
3.2. Effects
Minor technique variation produces random scatter around the true value. Because the direction and size of variation differs unpredictably between trials:
results are scattered above and below the true value rather than consistently displaced in one direction,
precision is reduced — repeated readings may not agree closely with each other,
accuracy is not affected — there is no consistent bias; results are centred on the true value on average,
the effect is larger when the procedure involves subjective judgement or fine motor control,
repeating measurements and averaging will reduce the effect, since random variations tend to cancel out over many trials.
3.3. Improvements
To reduce minor technique variation, standardise the procedure as precisely as possible and increase the number of trials.
Write a detailed, step-by-step method that specifies quantities, timings, and positions precisely, leaving as little as possible to individual judgement.
Practise the technique before data collection to improve consistency across trials.
Use mechanical or automated tools in place of manual steps where possible — for example, a magnetic stirrer instead of manual stirring, or a micropipette instead of a measuring cylinder.
Increase the number of trials and calculate a mean — random variation tends to cancel out as sample size increases.
Use the same researcher for all trials where technique consistency is critical, or train multiple researchers to follow an identical procedure.
Structured Question: Minor Technique Variation
A Year 8 class is investigating whether the drop height of a ball affects how high it bounces. Each student drops a tennis ball from four different heights — 25 cm, 50 cm, 75 cm, and 100 cm — and records the height of the first bounce. A video camera is mounted directly in front of the ruler so that bounce height is read from the footage at eye level, eliminating any parallax in the reading. The student releases the ball by hand for each trial. The teacher notices that the ball is not always released from exactly the same position — sometimes the student’s hand is slightly above or below the marked height.
(a) Identify the type of error introduced by releasing the ball by hand and classify it as random, systematic, or personal. (2 marks)
(b) Explain how this error would affect the group’s bounce height measurements. In your answer, refer to the direction of the error and its effect on the accuracy and precision of the results. (3 marks)
(c) The student repeats each trial five times and calculates a mean bounce height. Evaluate whether this would reduce the effect of the error identified in part (a). (2 marks)
(d) Describe one improvement the student could make to reduce this error before collecting data. (1 mark)
Reveal Answer Key
(a)
The error is minor technique variation, classified as a random error.
(1 mark for naming minor technique variation; 1 mark for random)
(b)
Because the ball is released slightly above or below the marked height, the effective drop height varies unpredictably between trials. On some trials the ball is dropped from slightly higher than intended, giving a higher bounce; on others it is dropped from slightly lower, giving a lower bounce. There is no consistent direction to the error — results are scattered both above and below the true bounce height for each drop height. (1 mark)
The precision of the results is reduced — repeated trials at the same drop height will give noticeably different bounce heights because the release position varies between trials. (1 mark)
The accuracy is not systematically affected — because the variation in release position is unpredictable in direction, the errors tend to cancel out over many trials and the mean is likely to be close to the true bounce height. (1 mark)
(c)
Repeating each trial five times and averaging would help reduce the effect of this error, although it cannot eliminate it entirely. (1 mark)
Because the release position varies unpredictably — sometimes too high, sometimes too low — some trials will give bounce heights that are too high and others too low. Averaging across multiple trials allows these opposing variations to partially cancel out, bringing the mean closer to the true bounce height. Increasing the number of trials further would improve this effect. (1 mark)
(d)
The student should use a mechanical release device — for example, a clamp or tube fixed at each marked height — so the ball is always released from exactly the correct position. (1 mark)
Part (a): accept “minor technique variation” or “small unavoidable variation in release position.” Do not accept “operator error” — the student is not making a one-off mistake or failing to follow the method; the variation is small and inherent in manual release across many trials. Do not accept “environmental variation” — the source of variation is the student’s technique, not an external environmental condition. Do not accept “parallax error” — the stem states that bounce height is read from video footage at eye level, explicitly eliminating parallax from the measurement.
Part (b): award the direction mark for a response that correctly identifies there is no consistent direction — results are scattered both above and below the true value. Do not award this mark for a response that identifies only one direction. Award the precision mark for correctly stating precision is reduced and linking this to the unpredictable variation between trials. Award the accuracy mark for correctly stating accuracy is not systematically affected because errors tend to cancel out across trials.
Part (c): repeating and averaging does help for random errors. Award both marks only if the student correctly identifies that averaging helps and explains why: opposing variations partially cancel out. A response that states repeating always reduces error without this reasoning should receive only 1 mark.
Part (d): accept “have another student observe and signal when the hand is exactly at the marked height before each release” or “mark the release point on a fixed stand and use it as a physical guide for hand position” as alternative valid responses. Do not accept “repeat measurements” as this has already been addressed in part (c) and only reduces rather than eliminates the error.