An observational study is one in which the data are collected on individuals in a way that does not
affect them. The most common observational study is the survey. Survey questionnaires were queues which are awarded to individuals who were selected from a population of interest. Investigations take many different forms: paper surveys sent by e-mail; websites; call-in polls conducted by television networks; and telephone surveys. When done properly, can check very useful tool for getting information. However, if not done properly, the investigation could lead to misinformation. Some problems contains incorrect wording of the questions, which can be confusing to people who have chosen to participate, but not answered, or a whole group of people who even chose a chance . The potential problems mean an investigation should be well thought out before it was given.
A drawback of the survey is that they can only report concerning ships between variables found; they can not claim cause and effect. For example, in one study researchers note that people who drink more than one Diet Coke a day tend to sleep fewer hours per night than those who drank no more than one per day, can not fulfill their Diet Coke is caused by lack of sleep. Other variables may explain the relationship, such as the number of hours worked per week. See all the information on investigations, their design and potential problems