Are entrepreneurs and self-employed people really happier than employees?

I recently read an article that says that self-employed and entrepreneurs are happier than people that are employees – because they have more freedom and flexibility. Is this the real reason? For me, thats not the full truth. Can you imagine that an unhappy person will start a company? I think that you need an intrinsic happiness and a positive attitude to become an entrepreneur – otherwise you will only see the problems, risks and failures, but not the possible outcome and positive emotions that might result in becoming an entrepreneur. Of course, having more freedom is great – but you also have to take more risks that might have a negative impact on the feelings. So if you ask entrepreneurs and freelancer about their feelings regarding “work”, you automatically get more positive feedback. Otherwise there might be more people that have a negative intrinsic feeling working as an employee. There you have at least your boss or maybe even your coworkers you can badmouth and get angry about. So for me, the real reason is that unhappy people will not start a company or work as freelancer. What do you think?