One of the advantages resulting from this approach for reporting results is the fact that it is possible to estimate the probability that an individual who is estimated to be in a particular literacy level will be able to perform the typical task in that level and in other levels. Unlike traditional test scores, which provide a single estimate of ability, these probability estimates offer a richer and more accurate reflection of the range of tasks that a person can be expected to perform successfully. After all, while each individual task used in an assessment is of some interest and importance, we are more likely to be interested in the class of tasks each item is intended to represent—that is, items that have similar characteristics and that we want to generalize outside the testing situation. Any assessment is likely to be more useful if we are able to generalize from the particular items used in the survey to the set of behaviors we are most concerned about.

These results mean that the literacy levels not only provide a means for exploring the progression of information-processing demands across each of the literacy scales, but they also can be used to help explain how the proficiencies demonstrated by various countries and various subpopulations reflect the likelihood they will respond correctly to a broad range of tasks used not only in IALS but to tasks having similar characteristics as well. In practical terms, this means that individuals performing at 250 on a literacy scale are expected to be able to perform the average Level 1 and Level 2 task with a high degree of proficiency. That is, they are expected to be able to perform these kinds of tasks with an average probability of 80% or higher. It is important to note that this does not mean they will not be able to perform correctly on literacy tasks in Levels 3 or higher. They will be expected to do so some of the time, but not with the same level of consistency.

The three tables shown here (Tables 4, 5, and 6) display the probability that individuals performing at selected points on each of the scales will give a correct response to tasks of varying difficulty. For example, Table 4 shows that a reader whose prose proficiency is 150 has less than a 50% chance of giving a correct response to the Level 1 tasks. Individuals whose proficiency score is 200, in contrast, have about an 80% probability of responding correctly to these tasks.

In terms of task demands, it can be inferred that adults performing at 200 on the prose scale are likely to be able to locate a single piece of information in a brief text when there is no distracting information, or if plausible but incorrect information is present but located away from the correct answer. However, these individuals are likely to encounter far more difficulty with tasks in Levels 2 through 5. For example, they would have only a 40% chance of performing the average Level 2 task correctly, an 18% chance of success with tasks in Level 3, and no more than a 7% chance with tasks in Levels 4 and 5.

In contrast, respondents demonstrating a proficiency of 300 on the prose scale have about an 80% chance or higher of succeeding with tasks in Levels 1, 2, and 3. This means that they demonstrate success with tasks that require them to make low level inferences and with those that entail taking some conditional information into account. They can also integrate or compare and contrast information that is easily identified in the text. On the other hand, they are likely to encounter difficulty with tasks where they must make more sophisticated textbased inferences, or where they need to process more abstract types of information. These more difficult tasks may also require them to draw on less familiar or more specialized types of knowledge beyond that given in the text. On average, they have about a 50% probability of performing Level 4 tasks correctly; with Level 5 tasks, their likelihood of responding correctly decreases to 40%.