# Statistics - True score (Classical test theory)

The true score is the score the truth that we try to estimate.

(Classical test|True score) theory asserts that raw scores are influenced by:

• bias,
• chance error,
• and true scores

## 3 - Formula

$$\href{Raw Score}{Raw\,Score} = \href{True score}{True\,Score} + \href{bias}{Bias}+Error$$

where:

• True Score is the score in a perfect world
• Bias is a systematic error. Example: An instrument that will always measure with the same difference. It has an effect on the entire distribution (It shift it right or left)
• Error: is also known as Chance error, or random chance error (For example, measurement of body temperature, if someone drink a coffer before measuring its temperature)