Element data window

The Element data window can most conveniently be viewed by pressing F5 (or choosing Window : Layout : Apply layout : Classic). This arranges the statistics windows in the classic shape first introduced in SuperMemo 3.0 (1988). When you double-click the element data window, you can view the element's repetition history.

This is a typical element data window after a repetition:

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Element data (left panel)

Element data displayed on the left of the element data window includes the following fields:

  • Repetitions - number of repetitions of the displayed element. If the element had been forgotten, the number of memory lapses is displayed in parentheses. Once the element is forgotten, the count of repetitions begins again. In the example presented in the figure, the item has been repeated 6 times and has not yet been forgotten (no lapses in parentheses in the Repetitions field)
  • Interval - current interval of the item, i.e. the number of days between Last repetition and Next repetition and the previous interval in days. Here the item have last been repeated in 1993 (6th repetition) and the interval was 2250 days (over 6 years). The interval between the 5th and 6th repetition was 768 days (over 2 years)
  • Last repetition - date of the last repetition of the item. Here the 6th repetition took place on July 20, 1993 and the current repetition which has just taken place is recorded on Sep 17, 1999
  • Next repetition - date on which the next repetition of the item should take place. Next repetition of this item should take place on Sep 17, 1999 and it has actually just been made (8th repetition has been scheduled on Sep 27, 2012; see the same row on the right side)
  • A-Factor - A-Factor associated with the currently displayed element. A-Factor is a rough measure of item difficulty and an accurate measure of the speed with which inter-repetition intervals will increase. The higher the A-Factor, the faster the increase in intervals. For items, the most difficult items have A-Factor equal to 1.2. For tasks and topics, A-Factors equal the increase in interval in a single review and may often be much less in value. Please note that Difficulty (below) is much more an accurate measure of item difficulty (as perceived by the user). A-Factor of 3.562 here falls into the average range typical for a majority of items in typical collections
  • U-Factor - the quotient of the previous interval and the next interval (in items that have been repeated only once, U-Factor equals the first interval). U-Factors make up an important element of the Algorithm SM-8. If you do not know the algorithm, U-Factors do not have much meaning to you. Here U-Factor is 2250/768=2.929 and indicates a significant increase in the interval (nearly threefold)
  • Forgetting index - planned probability of forgetting the item in the next repetition (in percent). Forgetting index can be changed to a desired value (e.g. with Forgetting index on the pop-up menu in the contents window). For example, if the forgetting index is 10%, you stand a 90% chance that you will remember the item in the next repetition. Here the forgetting index has been set at 16% which indicates that the item is probably not very important (the user can set the forgetting index as low as 3% for very important items)
  • Future repetitions - estimated number of repetitions of the item in the next thirty years. This value is easily derived from A-Factor, Repetitions, Forgetting index, and the matrix of optimal factors (see Algorithm SM-8). Please note that before SuperMemo 99, this estimation did not consider the forgetting index of the displayed item. Please click on the Forgetting index field to change this value and see how it changes the estimation of future repetitions. SuperMemo roughly predicts that there will still be three repetitions of the presented item in the next 30 years. As the 7th repetition has just taken place, the most likely number of repetitions before 2030 is two, of which one should take place in 2012
  • Ordinal - ordinal number associated with the element. Ordinals can be used to sort items in the pending queue, final drill queue, etc. The lower the ordinal, the higher the priority of the item. The presented item shows the ordinal 23570 (as set by the user). You cannot say if this number is high or low. It all depends on the ordinals of the remaining items in the collection.
  • Difficulty - difficulty of the displayed element estimated on the basis of the following parameters: Interval, Lapses, Repetitions, A-Factor, and First grade. The theoretical minimum for the difficulty is 0% and the theoretical maximum is 100%. Pending items have the difficulty estimated at 60%. This number decreases gradually with successful repetitions or increases with memory lapses. In a typical collection, the difficulty of items usually ranges from 16% to 64%. If the difficulty reaches beyond 65% you should have a close look at the formulation of your items (and potential causes of knowledge interference). The presented item is estimated to be difficult at 26% which indicates it is relatively easy to remember
  • First grade - grade obtained by the item in its first repetition. This value is important as the first grade vs. A-Factor correlation is used to quickly determine the A-Factor of items right after their first repetition. The presented item scored 5 (Bright) in the first repetition (NB: this number is just a heuristic guess due to the fact SuperMemo introduced the first grade record in 1995 while the item must have been memorized well before 1991 which was the date of its fifth repetition)
  • Type - type of the element: item, topic or task (see also: Topics vs. items) and its current status: dismissed, pending or memorized. The presented element is an example of a memorized item

Repetition data (right panel)

To understand repetition parameters displayed on the right of the element data window you should have a rudimentary knowledge of Algorithm SM-8. Here are the fields of the repetition parameters in element data window: 

  • Repetitions- number of repetitions of the displayed item (including the just-made repetition). If the item had been forgotten, the number of memory lapses is displayed after the colon. The number in the parentheses indicates the number of repetitions that the item would need to reach its current interval assuming the current value of the matrix of optimal factors and no memory lapses on the way. This hypothetical value is indeed used to index the matrix of optimal factors and the matrix of retention factors in computing the new values of individual entries at repetitions. The exemplary element above have just been repeated for the seventh time and has never been forgotten. Due to the relatively long interval, the repetition category is relatively high: 15.0
  • Optimum interval - optimum interval the item should use to ensure the forgetting probability determined by Forgetting index. The optimum interval before the next repetition is 4726 days (or over 13 years)
  • New interval - new interval before the next repetition. New interval might optimally be equal to Optimal interval; however, two factors may make these two values differ: (1) minor interval dispersion is needed to avoid scheduling a large number if repetitions on the same day (interval dispersion also speeds up the convergence of the optimization algorithm), and (2) some constraints imposed on the new interval may make it impossible for it to equal Optimum interval. For example, the new interval cannot be shorter than the old interval (Interval). For a low forgetting index, it is quite common that Optimal interval is shorter than Interval. This is not a reason for worry but might be an indication that the forgetting index is set too low. The interval after the presented repetition will increase from 2250 days (about 6 years) to 4759 days (over 13 years)
  • Next repetition - date on which the next repetition should take place (after the just-made repetition). Next repetition will be scheduled for 27th September 2012 (zero in the parentheses indicates that there are no other repetitions scheduled on that day)
  • New A-Factor - new value of A-Factor estimated for the display item after the just-made repetition. A-Factor was increased during the presented repetition from 3.562 to 4.73 as a result of a good grade
  • New U-Factor - new value of U-Factor (i.e. the quotient of the new interval and the old interval; see U-Factor above for more). U-Factor was changed from 2.929 to 2.115 (in other words, the present increase in interval is less than the last increase in the interval in 1993)
  • Expected FI - forgetting index derived from the interval (see the description of the Algorithm SM-8). Due to the long interval, the expected forgetting index was 21.8% (more than the requested forgetting index of 16%)
  • Estimated FI - forgetting index derived from the grade (see the description of the Algorithm SM-8). From the Bright grade the estimated forgetting index was computed as 0.2% (in other words, nearly perfect retention that had to result in a substantial increase in A-Factor)
  • Normalized grade - grade normalized for the optimum interval for the forgetting index equal 10% (see the description of the Algorithm SM-8). Here the normalized grade of 4.87 does not differ much from the actually scored grade of 5.0 (Bright)
  • R-Factor change - change of the R-Factor corresponding to the current repetition number (the one displayed in parentheses at Repetition) and A-Factor (displayed at A-Factor among element parameters described earlier)(see the description of the Algorithm SM-8). Only grades less than 3 (Pass) reduce the R-Factor (forgetting pulls the forgetting curve down reducing the interval needed to reach the same forgetting index). In the presented case, grade 5 increased the relevant entry of the R-Factor matrix from 3.804 to 3.849
  • O-Factor change - change of the O-Factor corresponding to the current repetition number (the one displayed in parentheses at Repetition) and A-Factor (displayed at A-Factor among Item parameters described earlier)(see the description of the Algorithm SM-8). For good grades, O-Factors also increase; however, as they come from smoothing R-Factors, these changes are less prominent. In the presented case, the O-Factor has not changed detectably (1.256)
  • Cases - number of repetition cases used to compute the values of O-Factor and R-Factor corresponding to the current repetition number (the one displayed in parentheses at Repetition) and A-Factor (at A-Factor in the previous column)(see the description of the Algorithm SM-8). Here 101 repetitions have been recorded for repetition category 15 and A-Factor around 3.6

1.3.21