And one economist has had a look at the details of how the results have been calculated.

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The April 5, 2011 Summary of Guardian Protective Cover Impact Testing by Oregon Ballistics Labs revealed that its series of testing demonstrated that the Guardian reduces the calculated Head Injury Criteria that results in brain injury.

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But how is it calculated - and what do the results actually mean?

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The results before December 2011 were calculated after the fact and weren't earned by any outside investors.

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Couple that with processes that seek certainty at the expense of creativity and calculated risk taking and you have the perfect mix for incremental results or worse yet, market failure.

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

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