Adult Literacy in America - National Center for Education Statistics ...

NALS
72 ......Section III
The response probabilities for two tasks on the prose scale are displayed in
Figure 3.1. The difficulty of the first task is measured at the 250 point on the
scale, and the second task is at the 350 point. This means that an individual
would have to score at the 250 point on the prose scale to have an 80 percent
chance (that is, a .8 probability) of responding correctly to Task 1. Adults
scoring at the 200 point on the prose scale have only a 40 percent chance of
responding correctly to this task, whereas those scoring at the 300 point and
above would be expected to rarely miss this task and others like it.
In contrast, an individual would need to score at the 350 point to have an
80 percent chance of responding correctly to Task 2. While individuals
performing at the 250 point would have an 80 percent chance of success on the
first task, their probability of answering the more difficult second task correctly
is only 20 percent. An individual scoring at the 300 point is likely to succeed on
this more difficult task only half the time.
Probabilities of Successful Performance on Two Prose Tasks by Individuals at
Selected Points on the Prose Scale
Probability of Successful Performance
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
150 200 250 300 350 400
Adults' Average Prose Proficiency
Task 1
Task 2
Source: U.S. Department of Education, National Center for Education Statistics, National Adult Literacy Survey, 1992.
An analogy may help clarify the information presented for the two prose
tasks. The relationship between task difficulty and individual proficiency is
much like the high jump event in track and field, in which an athlete tries to
jump over a bar that is placed at increasing heights. Each high jumper has a
height at which he or she is proficient. That is, he or she is able to clear the bar
at that height with a high probability of success, and can clear the bar at lower
Figure 3.1