Altogether, the adult population sampled represented approximately 191,000,000 adults. The data in Table 2.1 suggest that some 40 to 44 million adults are in the lowest level of skill, Level 1. Some 50 million are in Level 2, 61 million in Level 3, 28 to 32 million in Level 4 and 6-8 or so million adults are in Level 5.

Table 2.1

Percentage of adults in each of the five NALS skill levels for each literacy scale.

For comparison purposes, the percentage of people is given who would fall under the normal or "bell" curve at below -1 standard deviation (S.D.), between -1 to -0.5 S.D., between +- 0.5 S.D., between +0.5 and + 1.0 S.D. and above +1 S.D. The data indicate that by using the criterion-referenced standards of the NALS, the percentage of people in the lower two levels is well above what would be expected from a norm-referenced approach in which the mean and S.D. of the population is used to define levels of proficiency. The NALS approach greatly reduces the percentage of those at the highest level (Level 5).

What is The Meaning of The NALS Levels?

Being assigned to one of the five levels means that people at the average skill for a given level have an 80 percent probability of being able to perform the average tasks at the given level. For instance, the NALS report indicates that a person with a skill level of 200 would be assigned to Level 1, for which the average task difficulty is about 200 (averaged across the three literacy domains). This means that the person would be expected to be able to respond correctly to 80 percent of the average tasks in Level 1. However, this same person would be expected to be able to correctly respond to over 30 percent of the average tasks at Level 2, about 15 percent of the average tasks at level 3, 8 percent of the average tasks at Level 4 and about 5 percent of the average tasks at Level 5.^{1 p. 102}. This results from the fact that persons with skill levels below the difficulty level of an item may be able to perform the item correctly, though with a less than 80 percent probability of a correct response.

For example, consider a prose literacy task item that is of 279 difficulty for which a person needs a skill level of 279 to have an 80 percent probability of being able to perform the item. A person with a skill level of 250 has a probability of .62 of being able to perform the item. Because the person has a skill level of 250, on the NALS this would result in the person being assigned to Level 2. This would mean that the person has a .80 probability of being able to perform average Level 2 tasks. But note that the person would also be able to perform Level 3 tasks (which is where a task of 279 difficulty would fall), but not with as high a probability of success. In the NALS report, it is indicated that on either the prose, document or quantitative tasks, a person with a skill level of 250 can be expected to perform 50 out of 100 tasks that are at the average Level 3 task, 25 to 30 percent of the tasks at Level 4 and 10 to 20 percent of the tasks at Level 5, depending on the type of literacy scale under discussion ^{1 p 102} .