What is actually measured by the Implicit ociation Test?

The IAT uses reaction times to draw conclusions about potential underlying biases an individual may have. For example, the test may ask the participant to click on the word "good" whenever they see a white face and click on the word "bad" whenever they see a black face. Then they will switch the words so that you must click on the word good for the black face and the word bad for the white face. If we did not have any underlying biases for the ociation with certain groups and positive or negative words, then you would expect that it would always take the same amount of time to respond to whatever face was presented. However, there seems to be a trend that people are slower to connect minority faces with the word "good."