It also is possible that a specific treatment causes changes in the
participants so that the lingering aftereffects of the treatment carry over
into the next treatment (or treatments) and alter the participants’ scores.
For example, participants in a memory study may learn a new rehearsal
strategy in one treatment condition, and continue to use the strategy to
help improve their memory scores when participating in later treatment
conditions. Appropriately, these effects are called carry-over effects.
Notice that a testing effect, such as fatigue, comes from general experience
in the research study, whereas carry-over effects are caused by
experiencing a specific treatment.
Whenever participants go through a series of treatments in order,
their performance in one treatment may be influenced by experience
from a treatment earlier in the series. For this reason, testing effects and
carry-over effects are often grouped together under the general term
order effects.