The item total correlation is a measure of the reliability of a multi-item scale and a tool for improving such scales. It is the correlation between an individual item and the total score without that item. For example, if you had a test that had 20 items, there would be 20-item total correlations. For item 1, it would be the correlation between item 1 and the sum of the other 19 items. You can find correlations using a spreadsheet, statistical calculator, statistical software, or by hand.
Find the total score for each person by adding up the score for each item.
Subtract the score for the first item from the total for each person.
Correlate the scores on the first item with the scores calculated in Step 2. Exactly how to do this will vary depending on your calculator. This is the item total correlation for item 1.
Repeat steps 2 and 3 for each other item.