The following data show the pattern of results that was obtained in a study by Liguori and Robinson XXXXXXXXXXexamining how different levels of alcohol and caffeine consumption influenced response...

The following data show the pattern of results that was obtained in a study by Liguori and Robinson (2001) examining how different levels of alcohol and caffeine consumption influenced response time in a simulated driving test. The means show the average response time in milliseconds for different combinations of alcohol and caffeine. For these data:

Is there a main effect for alcohol?