Exactly how manyp values is a picture worth? A commentary on Loftus’s plot-plus-error-bar approach

Loftus (1993b) has recently argued that hypothesis testing is largely irrelevant and should be replaced with a “plot-plus-error-bar” (PPE) presentation of the data. We agree that such figures can be useful. However, they do not preclude standard hypothesis testing procedures, and they should be used to supplement rather than to supplant the latter. The insufficiency of PPEs is most apparent in the case of mixed designs and factorial within-subject designs. In such cases, there is no single value that is appropriate to represent the standard error.