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Precision vs Accuracy
Precision vs Accuracy
Two essential concepts in scientific measurement. Precision refers to reproducibility of measurements; accuracy refers to how close measurements are to the true value.
Comparison Table
| Feature | Precision | Accuracy |
|---|---|---|
| Definition | Reproducibility of results | Closeness to true value |
| Related Error | Random error | Systematic error |
| Measured By | Standard deviation | Percent error |
| Dartboard Analogy | Darts clustered together | Darts near bullseye |
| Can Be | Precise but inaccurate | Accurate but imprecise |
| Improved By | Multiple measurements | Calibration |
| Reported As | Significant figures, ± range | Percent error |
| Equipment Factor | Readability, technique | Calibration status |
Key Differences
- →Precision is about consistency; accuracy is about correctness
- →You can be precise without being accurate (consistent wrong answer)
- →Random errors affect precision; systematic errors affect accuracy
- →More measurements improve precision estimate but not accuracy
- →Calibration improves accuracy; careful technique improves precision
When to Use Precision
- ✓Evaluating measurement reproducibility
- ✓Reporting significant figures
- ✓Assessing random error
- ✓Determining standard deviation
When to Use Accuracy
- ✓Comparing to accepted values
- ✓Calculating percent error
- ✓Identifying systematic errors
- ✓Evaluating calibration needs
Common Confusions
- !Using precision and accuracy interchangeably (they are different)
- !Thinking more decimal places means more accurate
- !Not recognizing that averaging reduces random error, not systematic error
- !Confusing significant figures (precision) with percent error (accuracy)
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Common questions about this comparison
Yes! If a balance is miscalibrated, you might get very consistent (precise) readings that are all off by the same amount (inaccurate). The dartboard analogy: darts clustered tightly but far from the bullseye.
Significant figures indicate the precision of a measurement. More sig figs mean the measurement is more precise (smaller uncertainty). You should never report more sig figs than your least precise measurement allows.