9. We want to investigate whether drinking coffee causes stress. We have data coming from two different workplaces, an energy trading desk and a yoga studio. The trading desk causes its employees a lot of stress and provides them with an unlimited supply of free coffee. Based on the regression models below, which of the following is/are true? Select all that apply. (For simplicity, we will assume reverse causality, i.e. stress causing people to drink more coffee, is not an issue.) i) stressi : 0/ + lcoffeei + alagei + Olmalei l yltradem + u ii) stressi : as + scoffeei + 056L961 + Hsmalei + U? in) trader. : 7m + mcoffeei l wager l gmalei l 1],; (stress: stress level; coffee: dummy variable equal to 1 if coffee drinker, 0 otherwise; age: age; male: dummy variable equal to 1 if male, 0 iffemale; trader: dummy variable equal to 1 if working at the trading desk, 0 if working at the yoga studio) [I Zero conditional mean assumption is satisfied in regression ii. [3 Assuming ourtreatment is randomly assigned conditional on age, gender and workplace, the causal effect of coffee consumption on stress is equal to Bl. Al A E] Omitted variable bias is equal to: y 7T1 E] Conditional expectation of stressi for 35 years old male coffee drinkers working at the trading desk is given by: al + Bl l 0135