1. Percentile Ranking:
* Process: Each student's score is compared to the scores of all other students. Their grade is assigned based on their rank within the class's performance distribution. For example, the top 10% might receive A's, the next 20% B's, and so on.
* Calculation: This involves calculating the percentile rank of each student's score. This requires sorting all scores and then determining the percentage of students who scored below a particular student. Statistical software or spreadsheets can easily handle this calculation.
2. Z-Score Method:
* Process: This method uses the z-score (standard score) to determine how many standard deviations a student's score is from the class mean. Then, grades are assigned based on z-score ranges.
* Calculation:
* Calculate the mean (average) and standard deviation of all student scores. This gives a measure of the central tendency and spread of the data.
* Calculate the z-score for each student: `z = (student's score - mean) / standard deviation`
* Assign grades based on z-score ranges. For example:
* z >= 1.5: A
* 0.5 <= z < 1.5: B
* -0.5 <= z < 0.5: C
* -1.5 <= z < -0.5: D
* z < -1.5: F
* The specific z-score ranges are determined by the instructor and often reflect a normal distribution.
3. Predefined Percentage Ranges (Less True Relative Grading):
* Process: This method is sometimes called a "curve," but it's less genuinely relative. It predefines grade ranges based on a distribution, but doesn't use the actual class data distribution directly to set the boundaries.
* Calculation: The instructor decides percentages beforehand (e.g., top 15% get A's, next 25% get B's, etc.). They then find the scores that correspond to these percentages in the class's scores.
Important Considerations:
* Distribution Shape: The effectiveness of relative grading depends heavily on the actual distribution of scores. If the distribution is significantly skewed or flat, the results may not be representative.
* Inherent Bias: Relative grading can inadvertently penalize high-achieving classes and benefit low-achieving ones. A class where everyone performs exceptionally well might see fewer A's under relative grading than a class with a wider score distribution.
* Ethical Considerations: Some argue relative grading is unfair as it pits students against each other instead of evaluating them based on absolute performance standards.
In summary, relative grading involves transforming raw scores into grades based on their relative position within the class's score distribution. The specific calculation depends on the chosen method, but all methods aim to produce a predetermined grade distribution, often resembling a bell curve. However, it's important to be aware of the potential biases and drawbacks before implementing this grading system.