"What has precipitated the change is an increasing concern over the very variable performance of exam boards, " said a spokesman for the Independent Schools Council information service (Iscis).

BBC: Top schools' concern over exam results

Along with tackling pressure, athletes must also focus on self-confidence, which is the number-one variable for impacting high-level performance.

FORBES: Connect

What is more, performance can be much more variable.

BBC: NHS logo

Many cars, including the Mazda CX-5 and Volkswagen Golf, use variable valve timing to maximize fuel efficiency and performance.

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With full mobile compatibility and analog inputs, the Z22 is the first PC headset featuring Chat Boost, variable Bass and Treble Boost for a powerful audio performance across the sonic spectrum.

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Exams produce nice clear results, which can give useful clues about the performance of pupils, schools, teachers, methods and every other variable in the system.

ECONOMIST: Moves away from A-levels and GCSEs

About one-third or more of their pay is variable -- cash bonuses and SARs, tied to individual, business and stock market performance.

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Looking beyond logical changes to performance on products and services in terms of innovation, style and pricing, this new crisis-induced variable is key to our business and redefines the breakdown of the marketing mix.

FORBES: The Marketing Mix Is Changing. Are You Ready?