I want to use the CREDI Long Form, but I am only interested in one specific domain (for example, social-emotional development). Can I only use items that correspond to that domain?

We do not recommend this. Under normal circumstances, the scoring procedure for the CREDI Long Form takes into account information from all domains when producing its individual scores for the motor, language, cognitive, and social-emotional domains.  As such, even though the scores produced when items from some domains are missing are highly correlated and show strong agreement with the scores using the full Long Form, our analyses suggest that they are not exactly the same. More details are available in Appendix E of the Data Management & Scoring Guide.