But very common. But other factors may have occurred at the same time as the treatment, e.g., changed study style, teacher may have modified assignments, read of bad health effects of overweight, etc. Valid Designs Valid designs have two important criteria 1. Complete randomization - order of conditions is completely randomized for each subject. Works if you have a large number of different stimuli, or if each stimulus is presented many times to each subject, as it is unlikely that any particular order will have much influence.
Sequence is confounded with order.
Form each of the following rows by adding 1 to each number in the row above it. Form each of the following rows by adding 1 to each number in the row above it. Then, reverse the order of each row to create a second ordering. Both orderings must be used .