Read the following research abstract and answer the questions that follow. a 2013 study was undertaken by a team of researchers with doctorates in nutrition and medicine at an accredited research university. the study investigated risk factors for vitamin d deficiency in people who live in denmark and people who live in australia. by studying patterns in the population, the researchers demonstrated a correlation between the lack of sunny days in denmark and the high incidence of osteoporosis there, compared to the abundant sunny days and low incidence of osteoporosis in australia. however, the results could not rule out other factors in the subject’s diet or lifestyle as possible causes of the discrepancy in incidence. what is one limitation of this study, specifically with regard to generalizability?