Why should only the critical few data sets the health quality by Nash et al book be collected when collecting more data at the same time could make it easier to answer future questions?

Comment on the value and limitations of patient survey data sets in of the same book$.$ Why are functional status surveys valuable?

 

 Comment on variation in results over time in Chapters $4$ and $5$ on the same book$,$ including special cause and common cause variation, and explain what characterizes and differentiates special cause from common cause variation.