Why a blind guess is worth nothing.
Take a Section SA question for Medicine & Surgery: +22 if right, −5.5 if wrong. A blind guess is right one time in five. On average it gains a fifth of 22, which is 4.4 points, and loses four fifths of 5.5, which is also 4.4 points. The expected result is zero, exactly the same as omitting.
The same is true in every section and for both programmes, because each penalty is a quarter of its reward.
What ruling out an option is worth.
Each option you rule out with certainty raises your chance of being right, and the penalty no longer cancels the reward.
| Options left | Chance of being right | Question worth +22 | Question worth +16 | Question worth +10 |
|---|---|---|---|---|
| 5 | 1 in 5 | 0 | 0 | 0 |
| 4 | 1 in 4 | +1.38 | +1.00 | +0.63 |
| 3 | 1 in 3 | +3.67 | +2.67 | +1.67 |
| 2 | 1 in 2 | +8.25 | +6.00 | +3.75 |
The rule that follows: omit a question only when you cannot rule out a single option with certainty.
Near a threshold, play safe.
Expected points describe the average over many questions. Near a threshold, a single answer can matter more than the average, because a section below its threshold keeps you out of the ranking.
- If the answers you are sure of already put a section comfortably above its threshold, a blind guess adds risk for no expected gain. Omit it.
- If you may be below the threshold, answer every question where you can rule out an option.
- You cannot see your score during the test, but you can estimate it from the answers you are certain of.