Test and Measurements, discrimination/ Difficulty

Difficulty Index

This index is what tells us how many people got the item right

The lower / higher the percentage means what with the difficulty index

• Lower the percentage , the harder the item

• The higher the percentage, the easier the item

High Groups

This represents the top 27 % of test scores

Low Groups

This represents the bottom 27% of scores

Discrimination Index

This measures how effectively an item discriminates between high / low groups

• Represented as a decimal

What happens if The discrimination index is Positive 

This would mean there were more correct in high group than low group

What happens if The discrimination index is Negative

This would indicate there are more correct responses in the low group than high group

A perfect item has two characteristics, which are?

• A 50% difficulty level

• A 1.00 discrimination level