ACCURACY, PRECISION & RELIABILITY (PAPER 6 TIPS)
ACCURACY
• Definition: How close your result is to the true value. (CORRECTNESS)
• Example: A titration result of 25.0 cm³ when the true value is 25.1 cm³ is
accurate.
• How to improve accuracy:
o Use more precise apparatus (burette instead of measuring cylinder).
o Read measurements carefully at eye level to avoid parallax error.
o Use appropriate indicators (sharp end-point).
o Reduce heat loss in temperature experiments (insulate cup, cover with
lid).
PRECISION
• Definition: How close repeated results are to each other, even if not near the
true value. (CLOSENESS)
• Example: Three titration results of 24.5, 24.6, 24.5 cm³ are precise (but may not
be accurate if the true value is 25.1 cm³).
• How to improve precision:
o Repeat experiments until at least two results are concordant (within
±0.1 cm³ for titration).
o Use apparatus with smaller uncertainties:
▪ Burette → ±0.05 cm³
▪ Pipette → ±0.03 cm³
▪ Measuring cylinder (25 cm³) → ±0.5 cm³ (less precise than
burette/pipette)
▪ Thermometer (–10 to 110 °C, 1 °C graduations) → ±0.5 °C
o Consistent technique: swirl properly in titration, same amount of heat
applied in heating experiments.
RELIABILITY
• Definition: Whether your experiment would give similar results if repeated by
others, or by you on another day. (REPEATABILITY)
• How to improve reliability:
o Repeat the experiment and calculate an average.
o Identify and ignore anomalous results.
o Ensure fair test: only one variable changed at a time.
• Note: In IGCSE Paper 6, questions are much more likely to ask about accuracy
and precision than reliability.
COMMON SOURCES OF ERROR & IMPROVEMENTS
1. Measuring volumes
o Measuring cylinder has larger error (±0.5 cm³).
o Use burette (±0.05 cm³) or pipette (±0.03 cm³) for greater
accuracy/precision.
2. Reading scales
o Parallax error if eye not level → always read at eye level.
3. Heat loss in temperature experiments
o Solution cools before maximum temperature is measured → insulate
with cotton wool/polystyrene cup, cover with lid, measure temperature
quickly.
4. Gas collection
o Gas escapes before bung is inserted → insert quickly or use syringe
instead of inverted cylinder.
5. End-point in titration
o Colour change hard to see → use white tile underneath flask, consistent
drop size.
KEY EXAM TIPS FOR PAPER 6
• Accuracy vs Precision: Know the difference and use the correct term in answers.
• “How to improve accuracy” → use better apparatus, avoid heat loss, reduce
systematic errors.
• “How to improve precision” → repeat experiments, concordant results, use
apparatus with smaller uncertainty.
• Show working for averages in tables (don’t average rough results).
• Draw graphs carefully: use sharp pencil, neat scale, plot to half-square accuracy.
• If asked to identify improvements, always link the error → solution (e.g. “heat
lost → use insulation”).
• Don’t confuse:
o Accuracy = closeness to true value.
o Precision = consistency of repeated results.
o Reliability = repeatability/trustworthiness of experiment.
EXAM TREND: Expect Paper 6 questions mainly on accuracy and precision. Reliability
is less commonly tested, but good to know.