Please open chapter 9 (see the link of the book below) to answer this question, please summarize the following and use you own word 

1. Refer to Section 9.1 and summarize the following topics (use your own words) in

data collection and preparation, Reduction of Explanatory Variables (Hint: refer page

343-349).

(a) Controlled Experiment

(b) Controlled Experiment with Covariates.

(c) Confirmatory observational Studies.

(d) Exploratory Observational Studies.

Book pdf version: Applied Linear Statistical Models Fifth Edition:

https://d1b10bmlvqabco.cloudfront.net/attach/is282rqc4001vv/is6ccr3fl0e37q/iwfnjvgvl53z/Michael_H_Kutner_Christopher_J._Nachtsheim_JohnBookFi.org.pdf