Missing item scores versus missing total scores
In a multi-item questionnaire missing data often occurs. Missing data on these kinds of instruments can occur at the item level or at the total score level. Missing data on the item level, when one or more questions of the questionnaire are not filled out by the respondent, often impair the calculation of a total score. Mostly total scores are calculated by the sum or average of the item scores. That way, when one or more item scores are missing, the total score is missing as well. Missings at the total score level also occurs when the entire questionnaire is not filled-out by the respondent. In the Figure below you can see an example of a multi-item questionnaire with 10 items where item 2, 4 and 8 are missing which results in a missing total score.