The Curve of Forlearnting describes how we retain or rid of information that we take in. It's based on a one-hour lecture.

On day 1, at the beginning of the lecture, you go in knowing nothing,
or 0%, (where the curve starts at the baseline). At the end of the
lecture you know 100% of what you know, however well you know it (where
the curve rises to its highest point).
By day 2, if you have done nothing with the information you learned in that lecture, didn't think about it again, learn
it again, etc. you will have lost 50%-80% of what you learned. Our
brains are constantly recording information on a temporary basis: scraps
of conversation heard on the sidewalk, what the person in front of you
is wearing. Because the information isn't necessary, and it doesn't come
up again, our brains dump it all off, along with what was learned in
the lecture that you actually do want to hold on to!
By day 7, we remember even less, and by day 30, we retain about 2%-3%
of the original hour! This nicely coincides with midterm exams, and may
account for feeling as if you've never seen this before in your life
when you're studying for exams - you may need to actually re-learn it
from scratch.
You can change the shape of the curve! Reprocessing the same chunk of
information sends a big signal to your brain to hold onto that data.
When the same thing is repeated, your brain says, "Oh - there it is
again, I better keep that." When you are exposed to the same information
repeatedly, it takes less and less time to "activate" the information
in your long term memory and it becomes easier for you to retrieve the
information when you need it.
Here's the formula and the case for making time to review material:
within 24 hours of getting the information - spend 10 minutes reviewing
and you will raise the curve almost to 100% again. A week later (day 7),
it only takes 5 minutes to "reactivate" the same material, and again
raise the curve. By day 30, your brain will only need 2-4 minutes to
give you the feedback, "yes, I know that..."
Often students feel they can't possibly make time for a review
session every day in their schedules - they have trouble keeping up as
it is. However, this review is an excellent investment of time. If you
don't review, you will need to spend 40-50 minutes re-learning each hour
of material later - do you have that kind of time? Cramming rarely
stores information in your long term memory successfully, which makes it
harder to access the material for assignments during the term and exam
preparation.
Depending on the course load, the general recommendation is to spend
half an hour or so every weekday, and 1.5 to 2 hours every weekend in
review activity. Perhaps you only have time to review 4 or 5 days of the
week, and the curve stays at about the mid range. That's ok, it's a lot
better than the 2%-3% you would have retained if you hadn't reviewed at
all.
Many students are amazed at the difference reviewing regularly makes
in how much they understand and how well they understand and retain
material. It's worth experimenting for a couple weeks, just to see what
difference it makes to you!
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