According to a random sample of 31,364 adults aged 18 and older, Americans are exercising slightly more in 2012. This particular study was conducted with a random sample of adults living in all 50 U.S. states, selected using random-digit-dial sampling. This study could be generalized to all of America due to the fact that one can say with 95% confidence that the maximum margin of sampling error is plus or minus 1 percentage point. Gallup conducted this research and said their numbers were selcted at random within landline telephone numbers and cellular numbers, but mostly with landline numbers.
What we have learned in class is that landline phones are difficult to generalize due to the fact that numerous people have either put their landline phone on the "do not call registry" or have completely gotten rid of their landline for a cellular phone instead. The study does not say which time of day they called the research participants, which could play a large role in the type of lifestyle the participant lives. We could assume that if they called participants during the work day, they may be stay-at-home or unemployed adults who have the extra time to exercise compared to those with busy work styles.
Another speculation we discussed in class is truth. Participants may feel guilty for not exercising 30 or more minutes, three times a week so they could feel obligated to lie and say that they have been exercising to the researchers over the phone. There is also a downfall to this study due to the fact that some states sampled more than others (although at random) may have warmer weather year round, which makes exercising much easier for them compared to frigid winter states.