NAME

weightedGrader.pl

DESCRIPTION

A weighted grader that allows you to assign arbitrary percentages to the various answers in a problem. It also allows you to indicate that answering one part correctly will give you credit for some other part(s). This way, if there are several parts leading up to a "goal" answer, and the student produces the goal answer by some other means, he can be given full credit for the problem anyway.

WEIGHTED ANSWERS:

Each problem is assigned a weight (the default is 1). The student's score is then the sum of the weights for his correct answers divided by the total of the weights for all answers. (To assign weights as percentages, use integers that add up to 100, eg, use 40 and 60 for the weights for two answers.)

There are two ways to assign weights. The first is to use the WEIGHTED_ANS() routine (in place of ANS) to give an answer checker plus a weight.

Example:

WEIGHTED_ANS(std_num_cmp($ans1),2);

This assigns a weight of 2 to the corresponding numeric answer.

As with ANS(), WEIGHTED_ANS() can take more than one answer checker and weight.

Example:

WEIGHTED_ANS(
     std_num_cmp($ans1), 40,
     std_num_cmp($ans2), 60
);

This assigns 40% to the first answer and 60% to the second answer.

The second way of assigning a weight is through the weight_ans() function. This takes a single answer checker and weight and returns a new answer checker of the same type that has the desired weight. Thus

ANS(weight_ans(std_num_cmp($ans1),2));

is equivalent to the first example above.

The main purpose for weighted_ans() is so that weights can be used with UNORDERED_ANS(), or in other places where you want to use the weighted answer checker directly. For example:

UNORDERED_ANS(
    weight_ans(std_num_cmp($ans1),40),
    weight_ans(std_num_cmp($ans2),60),
);

produces two answers whose order doesn't matter, but the student will get 40% for getting $ans1 and 60% for getting $ans2 (no matter what order they appear in).

Note that the blank_cmp() answer checker has a weight of 0 by default. You can override this using weight_ans(); for example, weight_ans(blank_cmp(),1) makes the blank count the same as all the other answers. (If there are two or more non-blank answers, then having the blanks with weight 0 will allow the observant student to deduce the number of blank answers from the percentage for a single correct answer, provided all the non-blank answers are equally weighted).

Once you have given weights to the answers, you also need to install the weighted grader. Do this using the command

install_weighted_grader();

HAVING ONE ANSWER PROVIDE CREDIT FOR ANOTHER:

You may want to have a correct answer for one problem automatically give credit for one or more other parts of the problem. For example If several parts are used to lead up to the "real" answer to the problem, and the student produces that final answer without doing the intermediate parts (perhaps using some other method), then you may want to give the student full credit for the problem anyway. You can do so in the following way.

First, let us call the final answer the "goal" answer, and the answer that it would give automatic credit for the "optional" answer.

The optional answer blank must be a named answer, e.g.,

BEGIN_TEXT
You get credit for this answer: \{NAMED_ANS_RULE('optional',10)\}
When you answer this one: \{ans_rule(10)\}
END_TEXT

NAMED_ANS('optional',std_num_cmp(5));

Then for the goal answer, in place of ANS, use CREDIT_ANS, listing the optional answer as the second argument:

CREDIT_ANS(std_num_cmp(10),'optional');

You could also use NAMED_WEIGHTED_ANS for the optional answer, and supply a third argument for CREDIT_ANS, which is the weight for the goal answer. For example:

NAMED_WEIGHTED_ANS('optional',std_num_cmp(5),20);
CREDIT_ANS(std_num_cmp(10),'optional',80);

This way, if the student gets the optional part right (but not the goal), he gets 20%, and if he gets the goal right, he gets 100%.

One can use CREDIT_ANS to give credit for several other (named) answers at once by passing a list of names rather than a single one, as in:

CREDIT_ANS(std_num_cmp(10),['optional1','optional2'],80);

The weight_ans() routine, described in the section above, also can be used to give credit to another answer. In addition to the answer-checker and the weight, you can pass an answer name (or list of names) that should get credit when this one is right.

For example

ANS(weight_ans(std_num_cmp(10),80,'optional'));

is equivalent to

CREDIT_ANS(std_num_cmp(10),'optional',80);

One caveat to keep in mind is that credit is given to the optional answer ONLY if the answer is left blank (or is actually correct). Credit will NOT be given if the answer is incorrect, even if the goal answer IS correct.

When credit IS given, the blank answer is still marked as incorrect in the grey answer report at the top of the page, but the student gets awarded the points for that answer anyway (with no other indication). It is possible to cause the blank to be marked as correct, but this seemed confusing to the students.

Once you have issued the various ANS calls, you also need to install the weighted grader. Do this using the command

install_weighted_grader();