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Interpolated Median
The Interpolated median adjusts the median upward or downward by weighting the score positively or negatively based on the distribution of student responses.

Using the following scale, which is the current scale used for all SRIs.

Strongly Disagree = 1
Moderately Disagree = 2
Neither Disagree nor Agree = 3
Agree = 4
Strongly Agree = 5

If you received the following scores for one of your questions:

2 X Strongly Disagree
9 X Agree
10 X Strongly Agree

The median would be 4
The mean would be 4.19
And the interpolated median would be 4.44

The interpolated median shows that there were more responses above 4 than bellow it.  If the interpolated median would have been 3.6, that would be an indication that there were more responses bellow 4 than above it.

The following table shows what your median would be based on your interpolated median. 

If your Interpolated Media
is between
1 and 1.5 1
1.5 and 2.5 2
2.5 and 3.5 3
3.5 and 4.5 4
4.5 and 5 5

Reliability Assessment

The reliability assessment score measures how confident we are that the responses accurately represent all students registered in the course.

"The formula for the Reliability Assessment is based on a formula from "Elementary Survey Sampling" (by Richard L. Scheaffer et. al.). the constant 1.1 is the variance of the 5 rating scale question which are the most common in course evaluations and surveys.

The Input and Output

The formula takes the invited (Audience N) and responded (Responses n) counts as the inputs, it will output a value between 0 and 2.2. The closer the number to 0 the more reliable the data. "

Source: Shadi Khader - June 22, 2015, https://support.explorance.com


As your class size goes up, the number of respondents needed for us to have confidence in the representativeness of the data decreases.