list manipulation – Difference on average of y-axis between data sets

How can I calculate in Mathematica the difference on average between the y-axis of two data sets such?:

data1={{0, 38.9583}, {100, 54.9419}, {33, 53.5451}, {10, 43.8448}, {45, 
  57.9104}, {88, 56.0035}, {69, 64.0202}}

data2={{0, 46.3}, {9.7868, 51.646}, {29.8381, 63.8548}, {49.8925, 
  70.7243}, {69.9485, 74.71}, {89.9136, 67.8673}, {100, 58.8}}

Manually I am getting that on average the y axis of data2 is about 8-9 bigger than data1 but I am not sure how to do it properly in Mathematica when the x values do not match exactly