A recent analysis conducted by the Urban Institute investigated the relationship between urban green spaces and property values in several major cities. The study found that properties located within a quarter-mile of a public park experienced an average increase in value of 20% over five years compared to properties located more than a mile from any park. The researchers concluded that access to green spaces plays a significant role in enhancing property values in urban neighborhoods.
Despite these findings, critics of the study argue that property values are influenced by numerous factors, including economic conditions, local schools, and crime rates. They suggest that the study may not account for these variables and thus overstate the impact of green spaces on property values.
Which of the following, if true, would most seriously weaken the critics' argument?