An enhanced examination of Holland's consistency and differentiation hypotheses

• Holland's consistency and differentiation have not been well supported.
• A new means of operationalizing each using a cosine function was posited.
• These new indices were found to be better related to certainty and congruence.
• The new indices were related to occupational stability and career satisfaction.

The research support for Holland's concepts of consistency and differentiation has been equivocal (Nauta, 2010). To provide a reexamination of these concepts, a new method of operationalizing Holland's constructs of consistency and differentiation using the cosine fit function to the RIASEC score profile is proposed. The relation of these new indices to career certainty, congruence and the moderation of the congruence–certainty relation were examined in a sample of 118 college students (study 1). Support was found for the superiority of the cosine fit definitions of consistency and differentiation over the traditional representations. The cosine fit indices were further examined in a second study on 167 adults examining interest stability over 15 years. The cosine fit indices of consistency and differentiation were related to both occupational stability over 15 years and career satisfaction. The results suggest that the concepts of differentiation and consistency may still have merit but only with more exact methods of specification.