To Curve or Not to Curve

A version of this post appeared in the print series of The Innovative Instructor.

Yellow traffic signs showing a bell curve and a stylized graph referencing criterion-referenced grading.Instructors choose grading schemes for a variety of reasons. Some may select a method that reflects the way they were assessed as students; others may follow the lead of a mentor or senior faculty member in their department. To curve or not to curve is a big question. Understanding the motivations behind and reasons for curving or not curving grades can help instructors select the most appropriate grading schemes for their courses.

Curving defines grades according to the distribution of student scores. Grades are determined after all student scores for the assignment or test are assigned. Often called norm-referenced grading, curving assigns grades to students based on their performance relative to the class as a whole. Criterion-referenced grading (i.e., not curving) assigns grades without this reference. The instructor determines the threshold for grades before the assignment is submitted or the test is taken. For example, a 92 could be defined as the base threshold for an A, regardless of how many students score above or below the threshold.

Choosing to curve grades or use a criterion referenced grading system can affect the culture of competition and/or the students’ sense of faculty fairness in a class. Curving grades provides a way to standardize grades. If a department rotates faculty responsibility for teaching a course (such as a large introductory science course), norm-referenced grading can ensure that the distribution of grades is comparable from year-to-year. A course with multiple graders, such as a science lab that uses a fleet of graduate students in the grading, may also employ a norm referencing technique to standardize grades across sections. In this case, standardization across multiple graders should begin with training the graders. Curving grades should not be a substitute for instructing multiple graders how to assign grades based on a pre-defined rubric (The Innovative Instructor: “Calibrating Multiple Graders”).

In addition to standardizing grades, norm-referenced grading can enable faculty to design more challenging assignments that differentiate top performers who score significantly above the mean. More challenging assignments can skew the grade distribution; norm-referenced grading can then minimize the impact on the majority of students whose scores will likely be lower.

A critique of curving grades is that some students, no matter how well they perform, will be assigned a lower grade than they feel they deserve. Shouldn’t all students have an equal chance to earn an A? For this reason, some instructors do not pre-determine the distribution of grades. The benefit of using a criterion-referenced grading scheme is that it minimizes the sense of competition among students because they are not competing for a limited number of A’s or B’s. Their absolute score, not relative performance, determines their grade.

There are multiple ways to curve grades.

Image showing a bell curve.I. The Bell Curve

Normalizes scores using a statistical technique to reshape the distribution into a bell curve. An instructor then assigns a grade (e.g., C+) to the middle (median) score and determines grade thresholds based on the distance of scores from this reference point. A spreadsheet application like Excel can be used to normalize scores. CER staff can assist instructors in normalizing scores.

Image showing clumping.II. Clumping

The instructor creates a distribution of the scores and identifies clusters of scores separated by breaks in the distribution, then uses these gaps as a threshold for assigning grades.

 

Image showing quota system.III. Quota Systems

Often used in law schools, the instructor pre-determines the number of students who can earn each grade. The instructor applies these quotas after rank ordering student scores.

 

Image showing criterion-reference grading.IV. Criterion-reference grading

Using a pre-determined scale, assessments are based on clearly defined learning objectives and grading rubrics so students know the instructor’s expectations for an A, B, C, etc.

 

During the 2011 Robert Resnick Lecture at Johns Hopkins, Carl Wieman, Nobel Laureate and Associate Director for Science at the President’s Office of Science and Technology, argued that most instructors are not trained to create valid assessments of student learning. Curving can be used as a tool to adjust grades on a poorly designed test, but consistent use of curving should not be a substitute for designing assessments that accurately assess what the instructor wants students to learn by the end of the course. CER staff are happy to talk to faculty about defining learning objectives and/or strategies for designing challenging and accurate student assessment instruments.

Additional Resources

• Campbell, C. (2012). Learning-centered grading practices. Leadership. 41(5), 30-33

• Jacobson, N. (2001). A method for normalizing students’ scores when employing multiple gradersACM SIGCSE Bulletin. 33(4), 35-38.

Joe Champion’s Grading Transformation Spreadsheet. This spreadsheet automatically curves students’ scores after the instructor copies the scores into the spreadsheet and sets a variable defining the amount of curve.

Michael J. Reese, Associate Director
Center for Educational Resources


Image Sources: © Reid Sczerba, 2013.

GradeMark Paperless Grading

GradeMark is a paperless grading system that gives instructors the ability to add comments and corrections to assignments submitted electronically. It is a tool offered within Turnitin, the plagiarism detection software product used at JHU. With its drag and drop functionality, among other features, GradeMark has the potential to save instructors a great deal of time when grading online assignments.  It is also easily integrated with Blackboard.

(Note: In order to use GradeMark, online assignments must be created using Turnitin. If using Turnitin within Blackboard, accounts are automatically created for instructors and students through the Blackboard system. If using Turnitin outside of Blackboard, the instructor is responsible for creating separate accounts for each student. Please click here for more information on Turnitin’s integration with Blackboard.)

Screen shot showing example of using GradeMark

GradeMark contains several different grading features:

  • Dragging and Dropping Quickmarks – Quickmarks are frequently used comments that are readily available to drag and drop into a student’s assignment. While viewing an assignment, the instructor can select from a panel of standard Quickmarks that come with GradeMark, or from a custom set that s/he has created.  For example, the abbreviation ‘Awk.’ is a Quickmark indicating an awkward phrase. The ability to drag and drop Quickmarks to an assignment, instead of typing them over and over again, can save instructors a lot of time.
  • General Comments – Each assignment has a generous space where general comments can be added.  General comments can be used to further clarify any Quickmarks that were added as well as discuss the assignment as a whole.
  • Voice Comments – A recent addition to GradeMark is the ability to add voice comments. A voice comment can be added to the assignment lasting up to three minutes in length.  An instructor can use the built-in microphone in his/her computer to easily record the message.
  • Rubrics – Rubrics created within GradeMark can help streamline the grading process by using a ‘scorecard’ approach. Specific criteria and scores are defined in a rubric that is then associated with an assignment. Instructors grade the assignment by filling in the scores based on the evaluative criteria in the rubric. There is also the option of associating Quickmarks with rubrics when they are added to the assignment.

Students are able to view their graded assignments when the ‘post date’ is reached. The post date is set by the instructor when setting up the assignment. Students have the option to print or save a copy of the graded assignment and can view only their own submissions.

GradeMark Logo showing grade book and apple

Advantages:

  • Flexibility in marking up assignments – Quickmarks, rubrics, text, voice comments all available.
  • Time saved dragging and dropping reusable comments.
  • Increased consistency in grading.
  • Clear feedback to students, instead of ‘scribbled margins.’
  • Opportunity to provide more detailed feedback to students including links and resources.
  • No need to download assignments – everything is web-based, stored online.
  • If the instructor is using Blackboard, when the assignment is graded the grade is automatically transferred and recorded into the Blackboard Grade Center.

Amy Brusini, Course Management Training Specialist
Center for Educational Resources


Image sources: Amy Brusini screen shot of GradeMark example; GradeMark logo

Using a Rubric for Grading Assignments

Rubric comes from the Latin word rubrica meaning red chalk. In early medieval manuscripts the first letter of an important paragraph was often enlarged, painted in red, and called a rubric, leading to definitions of the term denoting the authority of what was written “under the rubric.” In the academic world the term has come to mean an authoritative rule or guide for assessment.

Instructor grading using a rubric

Most faculty, when preparing a graded assignment or exam, have expectations about how it should be completed, what will constitute a correct answer, or what will make the difference between an A and a C on a paper. Formalizing those thoughts into a written rubric – a template or checklist where those expectations are specified – has real advantages. First, it can save time when it comes to grading the assignment or test. Second, if you have Teaching Assistants, they will have a clear understanding of how to grade, and grading will be consistent across the sections. Third, it will make it easy to explain to students why they didn’t get that A they thought they deserved.

For a graded paper or project, it can be very helpful to share the rubric with the students when you give them the assignment. Seeing the rubric will help them to focus on what you feel is important. They will have a better understanding of the assignment and you will not only see better results, but have an easier time with the grading.

For more about creating rubrics see the CER’s Innovative Instructor print series article on Calibrating Multiple Graders: http://www.cer.jhu.edu/ii/InnovInstruct-BP_CalibratingGraders.pdf. For more on the reasons to use rubrics see: http://chronicle.com/blogs/profhacker/is-it-too-early-to-think-about-grading/22660.

Macie Hall, Senior Instructional Designer
Center for Educational Resources


Image source: Microsoft Clip Art, edited by Macie Hall