Statistics: Quantitative vs. Qualitative Data

Joe emails all his employees to explain to him why they are happy or not. The number of replies he gets will give him his answer.

Joe asks all the managers at the company branches to interview their employees about work enjoyment. They send Joe the transcripts of the interviews.

Joe leaves a complaint box outside his office and checks the box for complaints every week.

Joe emails all his employees a questionnaire asking them to rate their happiness at their job on a scale from $1$-$10$.

Joe gives some of his employees a $20$% raise and asks those employees whether they are happy or not.