A researcher examines the factors that influence student performance. She gathers data on 224 school districts in Massachusetts. The response variable is the students' mean score on a standardized test (Score). She uses five explanatory variables in her analysis: the student-to- teacher ratio (STR), the average teacher's salary (TSAL), the median household income (INC), the percentage of single parent households (SGL), and whether an urban (URB?) school district as opposed to rural or suburban. A portion of the data is shown in the accompanying table. SCORE STR(av. per teacher) TSAL( $000) INC($000) SGL% URB?(1=yes) 230.00 11.40 29.11 32.94 7.40 1 230.67 17.90 40.17 43.91 4.60 233.33 17.50 36.62 44.55 6.80 OOO 240.00 17.10 47.98 70.76 4.00