Re: Right-Minus-Wrong Grading

Dear CSCI-220 and CSCI-316 Students,

This FYI email explains how I will score any multiple-response items on this semester’s exams. Multiple-response items are fairly similar to multiple-choice items that have exactly one correct choice, but differ in that the number of correct choices may be ZERO, ONE, or MORE THAN ONE: Students are asked to write down ALL the correct choices (if there are any). Students who think none of the choices of a multiple-response item is correct will be required to write a specified phrase or word (e.g., “ALL FALSE” or “NONE”) that explicitly indicates this.

When Multiple-Response Items Appear

Not all of my exams include multiple-response items, but some do. (On my exams, multiple-choice items that have exactly one correct choice usually offer exactly FIVE choices, but multiple-response items that may have zero, one, or more than one correct choice usually offer exactly FOUR or at least SIX choices.)

Scoring Method

Many instructors score multiple-response items using the “all-or-none” method. However, I use another, rather more lenient, scoring method that’s consistent with the description of “Right Minus Wrong” scoring of Multi-Select questions on Brightspace quizzes. But, as mentioned above, in my multiple-response items it’s possible for none of the choices to be correct, in which case the student is required to write a specified word or phrase—e.g., “NONE” or “ALL FALSE”.

Calculation Details

This scoring method calculates the score based on:

(no. of RIGHT decisions) - (no. of WRONG decisions)

where a “RIGHT decision” is writing down a correct choice or NOT writing down an incorrect choice (and “WRONG decision” means the opposite): Students receive 0.25 point for each “RIGHT decision” but lose 0.25 point for each “WRONG decision”. But a student who makes more wrong decisions than right decisions will receive zero rather than a negative score.

Examples

Example Setup

Consider a multiple-response item that has two correct choices C1 & C2 and two incorrect choices C3 & C4.

Example 1: Writing “C1”

A student who writes just “C1” gets 0.25*3 - 0.25 = 0.5 pt. for making 3 right decisions and 1 wrong decision. (The 3 right decisions are to write C1, to not write C3, and to not write C4; the wrong decision is to not write C2.)

Example 2: Writing “C1, C2”

A student who writes “C1, C2” gets 0.25*4 = 1 pt. for making 4 right decisions and no wrong decision; this is the maximum possible score.

Example 3: Writing “C1, C4”

A student who writes “C1, C4” gets 0.25*2 - 0.25*2 = 0 for making 2 right and 2 wrong decisions. (The 2 right decisions are to write C1 and to not write C3; the 2 wrong decisions are to not write C2 and to write C4.)

Example 4: Writing “C1, C3, C4”

A student who writes “C1, C3, C4” gets 0 because s/he has made more wrong decisions than right decisions (1 right decision [to write C1] vs. 3 wrong decisions [to not write C2, to write C3, and to write C4]).

Example 5: Writing “C1, C2, C3”

A student who writes “C1, C2, C3” gets 0.25*3 - 0.25 = 0.5 pt. for making 3 right decisions and 1 wrong decision. (The 3 right decisions are to write C1, to write C2, and to not write C4; the wrong decision is to write C3.)

Summary for Four-Choice Items

When there are 4 choices (which has been quite common in my multiple-response items over the past 15 years), this scoring method means a student gets:

• 1 point if s/he makes 4 right decisions (i.e., his/her answer is completely correct)
• 0.5 point if s/he makes 1 wrong and 3 right decisions
• 0 if s/he makes 2 or more wrong decisions

See you in class tomorrow.

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T. Yung Kong, D.Phil.
Professor
Computer Science Department
Queens College, CUNY
Flushing, NY 11367, U.S.A.