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The Survey of Health, Ageing, and Retirement in Europe (SHARE) examines trends in aging among 120,000 people in Europe unfolding over many years. As is true of most longitudinal studies, this need for years of data collection results in high costs. By contrast, a relatively straightforward marketing study, such as one that is merely trying to identify the average amount customers spend per transaction at an online retailer, may not need a large budget because _____