**T-Scores**

• T-scores are ‘Transformed Scores’ used to standardise raw scores across the level or cohort.

• T-scores give the relative rank or position of a pupil’s performance compared to all the other pupils in that subject in the same exam.

• T-scores can be computed for individual subjects and then summed up as a single aggregate T-score, say in the case of PSLE.

• T-scores allow pupils to be ranked fairly.

**How are T-Scores calculated in PSLE?**

• As mentioned, T-score is the transformed or adjusted score a student will get for a subject, after factoring in the level or cohort’s mean and SD for that subject.

• Formula for T-Score

**X** = Raw score of student in the subject

**Y** = Average or Mean Score of the level or cohort

**Z** = Standard Deviation (SD) of the level or cohort Standard Deviation (SD) is the spread of the marks around the average.

**Why Standard Deviation (SD) matters?**

• Here is an example to illustrate that with the same mean, SD

or the spread of marks can vary.

**• Example 1 –**

Allan, Bernard and Charles have $45, $50 and $55 respectively. They have an average of $50 each.

**Example 2 –**

Dan, Edward and Frank have $10, $50 and $90 respectively. They also have an average of $50 each.

**• In Example 1,** the spread (from $45 and $55 to average of

$50) is smaller than the spread

**• in Example 2** (from $10 and $90 to average of $50)

**• Conclusion:** Despite having the same mean, Example 1’s data have a smaller SD or “spread from the mean” as compared to that of Example 2