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Sample Size for Surveys - Error alpha 
By tradition alpha is set to 5% but if the risks involved in the 'exposed' group is high, then it can be set to 10%. Conversely if the subject is not critical it could be set to 1%.
Alpha = 10% wil mean that with a little evidence the difference will be claimed significant.
Alpha = 1% will mean that you need a very strong evidence to claim significance.