Refer the article https://www.wikiwand.com/en/Search_advertising and answer the following questions:-

• Does sponsored search advertising on Google affect clicks for a website?
• What is the outcome variable of interest and how would you characterize the "treatment"?
• Indicate plausible sources of selection or omitted-variable bias that led you to believe that direct comparisons of outcomes from observational data would not yield a good measure of the causal effect