When a law is challenged as discriminatory, the outcome often depends on how demanding a test the court applies. That choice is made before the substance is examined.
Review operates at different intensities
Courts do not assess every law with the same rigour. Some measures are upheld if any plausible justification exists, while others must be shown to be necessary for a compelling purpose.
The difference is enormous in practice. Under the least demanding standard almost every measure survives; under the most demanding, very few do.
Because the standard largely determines the result, argument in these cases concentrates heavily on which standard should apply rather than on the merits.
The classification triggers the standard
Systems typically apply stricter review where a law distinguishes on grounds regarded as suspect, or where it affects an interest treated as fundamental.
Which grounds qualify has developed through case law, and courts have considered factors such as a history of exclusion, immutability of the characteristic and political representation.
Grounds not recognised as suspect are reviewed under the deferential standard, so a group's position within that classification scheme matters a great deal.
Purpose and fit are examined separately
Stricter review asks first whether the government's objective is sufficiently important, and objectives that are merely convenient or administratively tidy generally fail.
It then asks how well the measure fits that objective, examining whether it covers people it need not cover or misses people it should.
A poor fit suggests the stated purpose was not the operative one, which is why fit analysis frequently carries the decision.
Proportionality is the alternative framework
Many systems outside the tiered approach use a proportionality test, asking whether a measure pursues a legitimate aim, is suitable, is the least restrictive option and is balanced overall.
The structure differs but the questions overlap considerably, and both frameworks force the state to articulate and defend its reasoning explicitly.
Proportionality is applied along a spectrum rather than in fixed tiers, which gives courts more flexibility and makes outcomes somewhat harder to predict.
Burdens and evidence follow the standard
Under deferential review the challenger must show no plausible justification exists, which is difficult since the court may consider justifications never advanced.
Under stricter review the state carries the burden and must produce evidence, which changes what the litigation is about and what each side must gather.
These doctrines are constitutional and specific to each legal system, and they are revised by courts over time, so the applicable framework must be identified locally.