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Using data from 100 hospitals, a correlation of r = 0.78 is found between the size of a hospital (measured in number of beds) and the average length of patient stays (measured in days). Which of the following is true? Increasing hospital size must be the cause of longer patient stays. "Severity of illness" is a possible lurking variable that is behind this relationship. O There is a pretty strong positive linear correlation between number of beds and length of hospital stay