You are asked to study the causal effect of hours spent on employee training​ (measured in hours per worker per​ week) in a manufacturing plant on the productivity of its workers​ (output per worker per​ hour).

Required:
a. Choose a random group of employees to receive ten hours per week in additional training for a period of four weeks.​ Then, estimate the difference in productivity between workers who received the additional training and those that did not. Option _______ best describes this statement.
b. Data on hours spent on training a group of ten different employees in a certain day. Option __________ best describes this statement.
c. Data on hours spent on training the same employee for seven consecutive days. Option________ best describes this
d. Data on hours spent training for a group of ten individual employees for seven consecutive days. Option________ best describes this statement.

1. an observational time series data set.
2. an observational cross — sectional data set.
3. an ideal randomized controlled experiment.
4. an observational panel data set.