A study was conducted on the effects of long-term marriage (more than 10 years). Researchers gathered data from a sample of 4,563 adults in one small town and measured quite a few variables, in addition to the explanatory variable of marriage and the response variable of longer life span. According to a newspaper article summarizing the study, everyone in long-term marriages is more likely to be more physically active, at a healthy weight, and nonsmokers. All those who are not married are about 20% more likely to be deceased. Was this a valid conclusion? Explain.

This is a valid conclusion because the sample was large.
This is a valid conclusion because an observation was conducted.
This is not a valid conclusion because the sample was not random.
This is not a valid conclusion because there was no control group.