Ensuring content validity: an illustration of the process.

Assessing content validity is one of the most critical steps in instrument development. Neither statistical elegance nor sophisticated measurement strategies are substitutes for validity. Systematic in-depth approaches to the assessment of content validity are needed, including a priori and a posteriori procedures. In this manuscript the a priori approach of specifying an instrument's content domain is addressed along with the a posteriori procedure of having a panel of judges assess the validation of the items. This article focuses on the process used to assess the content validity. Data from the psychometric testing of the Postpartum Depression Screening Scale (PDSS) are used to illustrate this process. The PDSS is a Likert-type self-report composed of seven dimensions: Sleeping/Eating Disturbances, Anxiety/Insecurity, Emotional Lability, Cognitive Impairment, Loss of Self, Guilt/Shame, and Contemplating Harming Oneself. Items on the PDSS were generated from a series of qualitative research studies on postpartum depression. Content validity was assessed using two approaches to review the scale: (a) a panel of five content experts with professional expertise in postpartum depression, and (b) a focus group of 15 nurses knowledgeable in the field.