1. p < .05 is standard
2. What would be the advantages of
using p < .01 instead of p < .05?
Less likely to make Type 1 error (Less likely to mistake a chance difference between the group means for a treatment effect).
3. What would be the disadvantages of
using p < .01 instead of p < .05?
More likely to make a Type 2 error. That is, because you would have less power, you would be more likely to dismiss a real treatment effect as a coincidence.