Principals' Instructional Time Use

I came across this image in a post the other day.  "Pretty Charts: Principals Don't Spend Much Time On Instruction."   What caught my eye was how little time principals are spending on instructional time.  If principals are the instructional leaders of schools shouldn't they spend more time focusing on instructional issues?  

Couple of questions I have about the data:

• What questions did they ask to get to this data?
• How may principals participated in survey?
• What level were the principals? Elem, Middle, High?

More detailed information on the infographic.  

Has the role of the principal changed so that they are now more like CEO's, in charge of the "business" of the school and less of an instructional leader at the school?  The data shows they are not spending much of their time on instructional time.