### LON-CAPA Help

The Overall Problem Statistics page displays the following data about the problems currently in the course:

#Stdnts: Total number of students attempting the problem.
Tries: Total number of attempts to solve the problem.
Max Tries: Largest number of attempts to solve the problem by a student.
Mean Tries: Average number of attempts.
S.D. tries: Standard Deviation of the tries.
Skew Tries Skewness of the students' tries.
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Ö

 ĺ (Xi - Mean)3 / #Stdnts

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#YES: Number of students who solved the problem correctly.
#yes: Number of students who solved the problem by override.
%Wrng: Percentage of students who tried to solve the problem but were unable to.
DoDiff: Degree of Difficulty of the problem.

This statistics give a measure of how many attempts it took the students to get the problem correct. Those students who did not get the problem correct are not counted. A value close to 0 indicates most students who got the problem correct did so on the first attempt. A value close to 1 indicates many attempts were required for students to get the problem correct. A negative value indicates students were given points without attempting the problem. A value of 'nan' means there were no attempts made on the problem.

 1 - #YES+#yes Tries
DoDisc: Degree of Discrimination of the problem.

The students are grouped based on their scores on the sequence which contains the homework problem. The percent score of the bottom 25% of the students is subtracted from the percent score of the top 25% of the students. This yields a number from -1 to 1. 1.0 indicates all of the good students answered the problem correctly and none of the poor students answered it correctly. Conversely, a score of -1.0 indicates all of the good students got the problem wrong and the bad students did well.

weight: The weight of the problem in the course ("points"). The value shown is the weight of the problem for the individual computing the statistics. Individual student or section variations are not shown.

Sequence Statistics: Compiled statistics on problems based on their containing sequence, are also shown. The following data are shown:

#Items: The number of problem parts in the sequence.
Score Mean, Score STD, Score Max Score Min The mean, standard deviation, maximum, and minimum of the scores of the selected students on the given sequence.
Score N The number of the selected students who submitted answers to problem parts in the sequence.
Count Mean, Count STD, Count Max, Count Min: The mean, standard deviation, maximum, and minimum count of correct problem parts of the selected students on the given sequence.
Count N The number of the selected students who submitted answers to problem parts in the sequence.
KR-21 The KR-21 reliability statistic measures the internal reliability of a test or exam.

To compute the KR-21 reliability statistic the following formula is used:

 KR-21 = K K-1 · ćč 1- M ·(K-M) K ·s2 öř

Where

K is the number of items in your test
M the mean score on the test
s the standard deviation of the scores on your test