The image below is from this article in Psychological Science. A colleague pointed out two unusual things about it:
- According to the caption, the error bars show "±2.04 standard errors, the 95% confidence interval." I've only ever seen ±1.96 SE used for the 95% CI, and I can't find anything about 2.04 SE being used for any purpose. Does 2.04 SE have some accepted meaning?
- The text states that planned pairwise comparisons found significant differences for mean startle magnitude in error vs. correct predictable trials (t(30)=2.51, p<.01) and error vs. correct unpredictable trials (t(30)=2.61, p<.01) (the omnibus F test was also significant at p<.05). However, the graph shows the error bars for all three conditions overlapping substantially. If the ±2.04 SE intervals overlap, how can the values be significantly different at p<.05? The overlap is large enough that I'm assuming that the ±1.96 SE intervals also overlap.