In a 2017 study published in Scientific Reports, researchers (Mubanga et al. 2017) concluded that “dog ownership was associated with a lower risk of incident cardiovascular disease in single-person households and with lower cardiovascular and all-cause mortality in the general population.” Is this conclusion likely to be the result of an observational study or a controlled experiment? Can we conclude that owning a dog causes a decrease in cardiovascular disease from this study? Explain.