The researchers compiled data on the percentage of available jobs that require these four types of tasks and tracked the trends over a 30-year period (from 1969 to 1998). This information is displayed in Figure 1-5. In this figure the x-axis notes the years studied. The y-axis notes the change in the percentage of jobs that require the tasks, using 1969 as the base year. Thus, the figure shows that the percentage of jobs that require routine cognitive tasks (line marked with black triangles) was steady from 1969 to 1980 and then began a steady decline. Likewise, the percentage of jobs that require routine manual tasks (line marked with gray squares) was relatively steady until 1990 and then began to decline. The top two lines show that the percentages of jobs that require expert thinking (line marked with gray diamonds) and complex communication (line marked with black squares) have steadily increased since 1969. Murnane interpreted this information as demonstrating that expert thinking and complex communication are clearly tasks that are increasingly in demand by employers