Suppose you are a statistician consulting with a researcher who is trying estimate the effect of a new behavioral health intervention for children presenting with conduct disorders. He has data from two randomized controlled trials, each of which compares change in behavioral health symptoms between children who received the intervention to those who did not. However, one study measured behavioral health using the Child Behavioral Checklist (CBCL) and the other measured behavioral health using the Eyberg Child Behavior Inventory (ECBI). Although the CBCL and the ECBI are both well-established parent-rated survey measures of child behavioral health symptoms, they have different questions and response options, and are scored and interpreted differently. Therefore, a CBCL score and an ECBI score are not meaningfully comparable. The researcher wants to use all of the data he has from both studies to estimate the effect of the intervention. What advise would the researcher need and why?