While the income effects sum to zero, the substitution effects aggregate.

WSJ: Arthur B. Laffer: Unemployment Benefits Aren't Stimulus

It had an aggregate score of 229 - not precisely the sum of the three percentages, because of rounding - ranking it 35th out of 47 schools locally in the conventional league tables.

BBC: School 'value' shock is in store

Because of the way the aggregate is calculated it is not necessarily exactly the same as the sum of the three test results.

BBC: NEWS | UK | Education | Guide to the primary school tables