Some researchers believe that dogs may be beneficial in reducing cardiovascular risk in their owners by providing social support and motivation for physical activity (Mubanga et al. 2017). The purpose of this study was to investigate the association of dog ownership with incident of cardiovascular disease in the population of Sweden. Read the following excerpts from the study abstract and evaluate the study using the given questions.

Methods: All Swedish residents aged 40 to 80 years on January 1, 2001 (n = 3,987,937) were eligible for this study. The age range was chosen to exclude younger individuals at low risk of CVD and the elderly at low odds of owning a dog. All Swedish residents are covered by the public health care system, and all hospital visits are registered in the National Patient Register. We obtained death data from the Cause of Death Register and incident disease data from the National Patient Register. The main diagnosis in inpatient and outpatient care and underlying cause of death were used to define four incident disease outcomes: (1) acute myocardial infarction, (2) heart failure, (3) ischemic stroke, and (4) hemorrhagic stroke. Any occurrence of these diagnoses was additionally considered as a composite cardiovascular disease (CVD) outcome . . . Dog ownership was defined as periods registered or having a partner registered as a dog owner in either of the two dog registers (required for all dogs in Sweden.) 

Results: Dog ownership was inversely associated with risk of acute myocardial infarction, ischemic stroke, heart failure, and composite CVD. Dog ownership was inversely associated with cardiovascular mortality and all-cause mortality. Conclusions: 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. 

Our observational study cannot provide evidence for a causal effect of dog ownership on cardiovascular disease or mortality. Although careful attention was paid to adjusting for potential confounders in a set of sensitivity analyses, it is still possible that personal characteristics that we did not have information about affect the choice of not only acquiring a dog, but also the breed and the risk of CVD.

Evaluate the study based on the extracts from the study abstracts by answering the following questions:

a. What is the research question that the investigators are trying the answer?

b. What is their answer to the research question?

c. What were the methods they used to collect data?

d. Is the conclusion appropriate for the methods used to collect data?

e. To what population do the conclusions apply?

f. Have the results been replicated (reproduced) in other articles?