DEFINITION of 'LookAhead Bias'
Bias created by the use of information or data in a study or simulation that would not have been known or available during the period being analyzed. This will usually lead to inaccurate results in the study or simulation.
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BREAKING DOWN 'LookAhead Bias'
If an investor is backtesting the performance of a trading strategy, it is vital that he or she only uses information that would have been available at the time of the trade. For example, if a trade is simulated based on information that was not available at the time of the trade  such as a quarterly earnings number that was released three months later  it will diminish the accuracy of the trade's true performance.
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