I believe the answer is Observational study
In an observational study, the data input couldn't be controlled by researchers because it's relative to the subject.
This type of study usually being conducted in researchers that involve ethical measurement or Personal opinion.
The answer would be differential opportunity. This is
a theory that proposes that an individual’s socio-economic environment functions
to predetermine what are their chances of accomplishing financial achievement
or success over and done with genuine or illegal methods. For example: An
individual from low socioeconomic circumstances, who has few chances for
success, will use any methods at their removal to attain success.
The magnetic forces and the gravitational pull from the earth on its axis.
About 10% of American have ever taken a cruise.
If I've done my research correctly, this is about how many have actually taken a cruise. I would do some extra research to see if I'm correct or not.
