Scale validation via quantifying item validity using the Dm index.

Area of Science:

• Psychometrics
• Educational Measurement
• Psychological Assessment

Background:

• Traditional validity indices often rely on total test scores.
• Existing item selection techniques, like Piazza's P2 index, have limitations.
• There is a need for robust methods to assess construct validity at the item level, especially with limited data.

Purpose of the Study:

• To introduce and describe the Dm coefficient as a novel method for quantifying item construct validity.
• To provide an alternative to existing item selection techniques with substantial limitations.
• To offer a validity index suitable for small sample sizes where traditional methods like factor analysis or item response theory are not feasible.

Main Methods:

• The study adapts an item selection technique originally described by Piazza (1980).
• It introduces the Dm coefficient as a new index for item selection and validity.
• The Dm coefficient is presented as analogous to traditional criterion-related validity indices.

Main Results:

• The Dm coefficient provides a quantifiable measure of construct validity for individual items.
• This method offers an alternative to the limitations of Piazza's P2 index.
• The Dm coefficient functions similarly to established criterion-related validity indices.

Conclusions:

• The Dm coefficient is a valuable tool for assessing item construct validity, particularly in scenarios with small item or person samples.
• This method enhances psychometric analysis when traditional approaches are inappropriate.
• The paper provides a practical example of applying the Dm coefficient technique.