Forgetting Curve
The
forgetting curve illustrates the decline of memory retention in time.
In
1885, Hermann Ebbinghaus discovered the exponential nature of forgetting. The
following formula can roughly describe it:


Where R is memory retention, S is the relative strength of
memory, and t is time.
Ebbinghaus studied the memorization of nonsense syllables,
such as "WID" and "ZOF". By repeatedly testing himself
after various time periods and recording the results, he was able to
describe the shape of the forgetting curve.
The
forgetting curve describes the exponential curve that illustrates how
fast we tend to forget the information we had learned. The sharpest decline is in the first twenty minutes, then in the first hour, and then the curve evens off after about one day.
The speed of forgetting depends on a number of factors such as the
difficulty of the learned material (e.g. how meaningful it is), its
representation and physiological factors such as stress and sleep. The basal
forgetting rate differs little between individuals. The difference in
performance (e.g. at school) can be explained by mnemonic representation
skills.
Basic training in mnemonic techniques can help overcome those differences in
part. The best methods for increasing the strength of memory are:
 better memory representation
(e.g. with mnemonic techniques)
 repetition based on active
recall (esp. spaced repetition)
Each repetition in learning increases the optimum interval before the next
repetition is needed (for nearperfect retention, initially repetitions may
need to be made within days, but later they can be made after years).
The speed of forgetting depends on a number of factors such as the
difficulty of the learned material (e.g. how meaningful it is), its
representation and physiological factors such as stress and sleep. The basal
forgetting rate differs little between individuals. The difference in
performance (e.g. at school) can be explained by mnemonic representation
skills.
In a typical schoolbook application (e.g. learning word
pairs), most students remember only 10% after 3–6 days (depending on the
material Therefore, 90% of what was learned is forgotten.
A typical graph of the forgetting curve shows that humans
tend to halve their memory of newly learned knowledge in a matter of days or
weeks unless they consciously review the learned material.
A 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 24 minutes to give you the
feedback, "
Spacing Effect
