Define accuracy and precision also a note on types of accuracy and precision.

Accuracy

Accuracy means how close a measured value is to the true (actual/real) value.

In easy words: it tells you if your result is correct or not.

Example: If the true weight of an object is 10 grams, and your measurement shows 9.9 grams, that's accurate — it's very close to the real value.

Precision

Precision means how close several repeated measurements are to each other, regardless of whether they are correct or not.

In easy words: it tells you if your results are consistent/repeatable.

Example: If you weigh the same object 3 times and get 9.9g, 9.9g, and 9.8g — these values are close to each other, so this is precise, even if the true value is actually 10.5g (in that case it's precise but not accurate).

Types of Accuracy

Accuracy can be expressed/determined in different ways:

1. Absolute Accuracy

The actual difference between the measured value and the true (real) value.

Absolute Accuracy = Measured Value − True ValueExample: True value = 10g, Measured = 9.8g → Absolute accuracy = 0.2g

2. Relative Accuracy

The difference expressed as a percentage of the true value. This is more commonly used because it's easier to compare across different scales.

Relative Accuracy (%) = (Measured Value − True Value) / True Value × 100Example: (9.8 − 10) / 10 × 100 = −2% (i.e., 2% low)

Accuracy is also commonly determined through methods like:

• Comparison with a reference/standard method
• Recovery studies (adding a known amount of substance and checking how much is "recovered")
• Standard addition method

Types of Precision

Precision has 3 main types, based on the conditions under which measurements are repeated:

1. Repeatability (Intra-day Precision)

• Same analyst, same instrument, same lab, same day, short time interval
• Also called intra-assay precision
• Tells you how consistent results are under the most controlled conditions

2. Intermediate Precision (Inter-day Precision)

• Same lab, but with variations — different day, different analyst, or different instrument
• Also called inter-assay precision
• Shows how consistent results are within the same lab over time

3. Reproducibility (Inter-laboratory Precision)

• Different labs, different analysts, different equipment, possibly different countries
• Tests whether the method gives consistent results everywhere it's used

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