What is the Item Discrimination Index? How to Calculate?
- 25 Eyl 2023
- 1 dakikada okunur
What is the Item Discrimination Index?
Item Discrimination Index is a mathematical value that measures the power (quality) of each item in a test to distinguish between those who know and those who do not know.
This index is used to determine how well each item of an exam or test discriminates. That is, the better an item can distinguish a good or bad student, the higher its discrimination.
How is it calculated?
In its simplest terms, it is calculated based on the difference between the number of people who answered an item correctly in the successful and unsuccessful groups. Now let's expand on this a little more...
Item Discrimination Index is calculated based on the difference between the number of people who answered an item correctly in the successful and unsuccessful groups.
rjx=" 𝑡𝑎 𝑑𝑜ğ𝑟𝑢 𝑐𝑣𝑝)/(𝐺𝑟𝑢𝑝𝑙𝑎𝑟𝑑𝑎𝑛 𝑏𝑖𝑟𝑖𝑛𝑑𝑒𝑘𝑖 𝑡 𝑜𝑝𝑙𝑎𝑚 𝑐𝑒𝑣𝑎𝑝𝑙𝑎𝑦𝚤𝑐𝚤 𝑠𝑎𝑦𝚤𝑠𝚤)
It is found with the formula. Therefore, we need successful and unsuccessful groups. For this, if we are working on all participants, first the upper 27% and lower 27% are selected. Here,
Successful Group --> Parent Group
Failed Group --> Subgroup
Here, the correct option is option D. Accordingly, 30 students in the upper group and 10 students in the lower group answered correctly. Additionally, there are 50+50=100 students in the upper and lower groups. When the values were placed on the formula, the result was 0.40.
So what does this mean?
The result is evaluated as follows:
0.40-1.00: Highly discriminatory
0.30-0.40: Moderate discrimination
0.20-0.30: Low level of discrimination
0.00-0.20: Very low level of discrimination
<0.00: Reverse running (invalid)
Accordingly, the result we found shows that the substance is highly discriminatory.
You can find what we explained in more detail in our related video.