Answer
It is better to study a time series of the percent increase for each year.
Work Step by Step
The time series of the data would show a constant increase in tuition since 1980 (in terms of 2013 dollars). Since we are looking for patterns, the percent increase would fluctuate. This fluctuation in the percent increase would not always show an upward trend in the percent increase (i.e. after a 5% increase, there is a 2% increase).
