forum 9: week of 12 March: Fisher and the design of experiments
Thanks for your question, Andrea. Both the 5% and 1% significance levels are common. For the ones who think 5% is too high, most of them tend to go with 1% for the significance level because a lower significance level is (supposedly) more desirable. Why 5% is too high a significance level is incredibly subjective, and more often than not relies on factors specific to the discipline undergoing investigation that I am unable to speak of here. In any case, this is the view on significance levels among researchers that is most articulated. The 5% significance level has become known as a standard because of how frequently it has been used, and the fact that some journals have made it as a rule for publications. That is, if results don't reach the 5% significance level, then those studies are generally not accepted in those journals. I am quite skeptical myself on the merits of this idea about the 5% significance level as the standard, and support a view on significance levels that does not agree with the most articulated view I mentioned earlier. Thus, I am not quite the right person to ask what circumstances lead researchers to sometimes use a 1% significance level. Needless to say that the debate on how to correctly interpret significance levels is nowhere near reconciliation, though one of the goals of my term paper for PHIL 440 is to shed light on this topic. Also, I found one article on the internet that tries to address this question of why 5% is a common significance level: http://www.jerrydallal.com/LHSP/p05.htm. I hope this helps. Let me know if you have any more questions on this topic.