Professor Paul Nation (Victoria University of Wellington) is a leading expert on Vocabulary Acquisition, and he describes scientific studies that show the following:
The order of the words in a list has other effects on learning. In
general, items at the beginning of the list and at the end of the list are
learned better than items in the middle. These are called the primacy
and recency effects (Baddeley, 1990: 52). Putting difficult words near
the beginning is also a way of ensuring that they get more attention.
Pyc and Rawson (2007) compared a drop-out schedule (where
learned items were put aside and the more difficult items were focused
on) with a conventional schedule (where each item got equal atten-
tion). The drop-out schedule was more efficient. So, it is a good idea to
allocate more repetitions to the difficult items and less to the easy ones
(see also Atkinson, 1972).
Hence, would it be possible to add to Anki an option to "Review cards with most lapses first ?
Source: Learning Vocabulary in Another Language. Paul Nation (Cambridge. Second Edition. 2013)
Chapter 11, ‘Deliberate learning from word cards’, page 459