Signed percentage changes
Compute the percentage change in quantity and in price, each with its sign.
AQA 8136 · Price elasticity of demand
Price elasticity: the sign, then the magnitude
The sign and interpretation marks. PED is computed with signed percentage changes; the magnitude is taken only at the classification step, and revenue direction follows from the classification.
Reviewed family · Studara-authored items · No grade-uplift claim
The lost mark
One answer. Several places the method can fail.
Studara does not reduce the response to right or wrong. The reviewed contract checks these states independently.
PED value
Divide the change in quantity by the change in price.
Classify and infer
Take the magnitude to classify as elastic or inelastic, then state the effect on total revenue.
Why it goes wrong
The diagnosis stays uncertainty-safe.
A wrong response can support a specific measured diagnosis. A blind multiple-choice diagnostic records only a possible cause until later working provides stronger evidence.
01
The error
Discarding the negative sign during the calculation and then classifying from the raw number, or inferring what happens to revenue from the direction of the price change alone.
02
Why it survives revision
PED is conventionally quoted as a magnitude, so dropping the sign looks like correct practice rather than an error. It only becomes visible on the question that asks what happens to total revenue.
The worked repair
Repair the smallest broken step.
Teaching is not evidence. This one move is the repair; the proof checks begin after it disappears.
Compute both percentage changes with their signs, divide, and take the magnitude only when classifying as elastic or inelastic.
What happens after the repair
Correction is the start, not the result.
Immediate
Asked again straight away, on a different question
The repair leaves the screen and a new authored item checks the method unassisted. Being taught something is never evidence that it was learned, so this is the first stage that counts at all.
Delayed
Asked again after at least 1 day
A parallel form of the same method, unassisted, with the repair no longer on screen. A retest in the same session does not count.
Transfer
Asked again when the surface changes
The transfer form gives the elasticity and asks what a price CUT does to revenue, so the relationship has to be reasoned in the other direction.
Exam
Asked again under exam conditions
Timed, carrying the mark tariff, in an exam-like response format and aligned to the specification. Any one of those missing and the evidence is refused.
REVIEWED BOUNDARY
This page covers one reviewed family: Price elasticity of demand. Preserve percentage-change signs, calculate PED, classify its magnitude and infer the direction of total revenue. Other families within the same GCSE Economics topic are outside this reviewed journey, and Studara does not apply the proof label to material that has not been reviewed. No grade-uplift claim is made anywhere on this site.
Straight answers
Before you use this guide.
Should price elasticity of demand be negative?
The calculated value is normally negative, because price and quantity move in opposite directions. The magnitude is what you classify by — but dropping the sign during the calculation causes errors on the revenue question.
What happens to revenue if demand is elastic and price falls?
Revenue rises. When demand is elastic, quantity changes proportionally more than price, so a price cut increases total revenue.
Does Studara guarantee a higher grade?
No. Studara has not run a controlled outcome study and publishes no grade-uplift claim. What has been measured, what is withheld, and the metric that failed its bar are all on the public evidence page.
Turn this method into evidence