Thursday, October 15, 2015

Type I (false positive) and Type II (false negative) errors

I've seen a lot of explanations of Type I and Type II errors, but this photo collage is my favorite.

When we set a confidence level, what we are doing is setting the probability of Type I error. The null hypothesis can always be interpreted as "nothing special is happening" and Type I errors mean we think something special is happening when it isn't. In many cases, false positive are more disruptive than false negatives and we are more interested in limiting Type I errors than we are in limiting Type II errors. There will be more discussion of this in class on Oct. 15 and the note will also be posted here.


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