What level of measurement was the independent variable?

Let’s look at the use of ANOVA in the following nursing research article:
Özden, D., & Görgülü, R. S. (2015). Effects of open and closed suction systems on the haemodynamic parameters in cardiac surgery patients. Nursing in Critical Care, 20(3), 118–125. doi:10.1111icc.12094

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TABLE 10-1 SBP for Caucasian, African American, and Latino Men Caucasian 165 110 134 112 178 156 123 African American 108 196 178 145 164 127 139 Latino 110 143 123 120 118 146 124 123 126 118 119 142 123 156 150 114 122 116 140 128 132 118 142 116 154 119 130 121