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International Adult Literacy Survey (IALS)


Statistics Canada and ETS, a private testing organization in the United States, coordinated the development and management of IALS. These organizations were assisted by national research teams from the participating countries in developing the survey design. The survey design for the 1994 IALS is described below


The IALS target population was the civilian, noninstitutionalized population ages 16 to 65 in each country; however, countries were also permitted to sample older adults, and several did so. All IALS samples excluded full-time members of the military and people residing in institutions such as prisons, hospitals, and psychiatric facilities.

For the United States, the target population consisted specifically of civilian noninstitutionalized residents ages 16 to 65 in the 50 states and the District of Columbia, excluding members of the armed forces on active duty, those residing outside the United States, and those with no fixed household address (i.e., the homeless or residents of institutional group quarters, such as prisons and hospitals). 


IALS was designed to provide data representative at the national level. Each country that participated in IALS agreed to draw a probability sample that would accurately represent its civilian, noninstitutionalized population ages 16 to 65. The final IALS sample design criteria specified that each country’s sample should result in at least 1,000 respondents, the minimum sample size needed to produce reliable literacy proficiency estimates. Given the different sizes of the population of persons ages 16 to 65 in the countries involved, sample sizes varied considerably from country to country (ranging from 1,500 to 8,000 per country), but sample sizes were sufficiently large in all cases to support the estimation of reliable item parameters using Item Response Theory (IRT).

IALS countries were strongly encouraged to select high-quality probability samples because the use of probability designs would make it possible to produce unbiased estimates for individual countries and to compare these estimates across the countries. Because the available data sources and resources were different in each of the participating countries, however, no single sampling methodology was imposed. Each IALS country created its own sample design. All countries used probability sampling for at least some stages of their sample designs, and some used probability sampling for all stages of sampling. Sampling designs were approved by expert review.

The sample for the United States was selected from a sample of individuals in housing units who were completing their final round of interviews for the U.S. Census Bureau’s Current Population Survey (CPS) in March, April, May, and June 1994. These housing units were included in the CPS for their initial interviews in December 1992 and January, February, and March 1993.

The CPS is a large-scale continuous household survey of the civilian noninstitutionalized population age 15 and over. The frame for the CPS consisted of 1990 decennial census files, which are continually updated for new residential construction and are adjusted for undercount, births, deaths, immigration, emigration, and changes in the armed forces. The CPS sample is selected using a stratified multistage design. Housing units that existed at the time of the 1990 population census were sampled from the census list of addresses. Housing units that did not exist at that time were sampled from lists of new construction, when available, and otherwise by area sampling methods. Occupants of housing units that came into existence between the time of the CPS sample selection and the time of the IALS fieldwork had no chance of being selected for IALS.

The IALS sample was confined to 60 of the 729 CPS primary sampling units (PSUs). Within these 60 PSUs, all persons 16 to 65 years of age in the sampled housing units were classified into 20 cells defined by race/ethnicity and education. Within each cell, persons were selected for IALS with probability proportional to their CPS weights, with the aim of producing an equal probability sample of persons within cells. A total of 4,901 persons were selected for IALS. IALS interviews were conducted in October and November 1994. 


Assessment Design

The success of IALS depended on the development and standardized application of a common set of survey instruments. The test framework explicitly followed the precedent set by the National Adult Literacy Survey, basing the test on U.S. definitions of literacy along three dimensions—prose literacy, document literacy, and quantitative literacy—but extending the instruments into an international context. Study managers from each participating country were encouraged to submit materials such as news articles and documents that could be used to create tasks with the goal of building a new pool of literacy tasks that could be linked to established scales. IALS field tested 175 tasks and identified 114 that were valid across cultures. Approximately half of these tasks were based on materials from outside North America. (However, each respondent was administered only a fraction of the pool of tasks, using a variant of matrix sampling.)

Each IALS country was given a set of model administration manuals and survey instruments as well as graphic files containing the pool of IALS literacy items with instructions to modify each item by translating the English text to its own language without altering the graphic representation. Certain rules governed the item modification process. For instance, some items required respondents to perform a task that was facilitated by the use of keywords. The keyword in the question might be identical to, similar but not exactly the same as, or a synonym of the word used in the body of the item, or respondents might be asked to choose among multiple keywords in the body of the item, only one of which was correct. Countries were required to preserve these conceptual associations during the translation process. Particular conventions used in the items—for example, currency units, date formats, and decimal delimiters—were adapted as appropriate for each country.

To ensure that the adaptation process did not compromise the psychometric integrity of the items, each country’s test booklets were carefully reviewed for errors of adaptation. Countries were required to correct all errors found. However, this review was imperfect in two important respects. First, it is clear that countries chose not to incorporate a number of changes that were identified during the course of the review, believing that they “knew better.” Second, the availability of empirical data from the study has permitted the identification of several additional sources of task and item difficulty that were not included in the original framework, which was based on research by Irwin Kirsch of ETS and Peter Mosenthal of Syracuse University. (See 1990 publication, “Exploring Document Literacy: Variables Underlying the Performance of Young Adults,” by I.S. Kirsch and P.B. Mosenthal in Reading Research Quarterly 25: 5–30.) Item adaptation guidelines and item review procedures associated with subsequent rounds of IALS data collection were adapted to reflect this additional information.

The model background questionnaires contained two sets of questions: mandatory questions, which all countries were required to include; and optional questions, which were recommended but not required. Countries were not required to field literal translations of the mandatory questions, but were asked to respect the conceptual intent of each question in adapting it for use. Countries were permitted to add questions to their background questionnaires if the additional burden on respondents would not reduce response rates. Statistics Canada reviewed all background questionnaires (except Sweden’s) before the pilot survey and offered comments and suggestions to each country.


Data Collection and Processing

IALS data for the first round of countries were collected through in-person household interviews in the fall of 1994. Each country mapped its national dataset into a highly structured, standardized record layout that it sent to Statistics Canada. Further description follows.

Reference dates. Respondents answered questions about jobs they may have held in the 12 months before the survey was administered.

Data collection. Statistics Canada and ETS coordinated the development and management of IALS. Participating countries were given model administration manuals and survey instruments as well as guidelines for adapting and translating the survey instruments and for handling nonresponse codings.

Countries were permitted to adapt these models to their own national data collection systems, but they were required to retain a number of key features: (1) respondents were to complete the core and main test booklets alone, in their homes, without help from another person or from a calculator; (2) respondents were not to be given monetary incentives for participating; (3) despite the prohibition on monetary incentives, interviewers were provided with procedures to maximize the number of completed background questionnaires and were to use a common set of coding specifications to deal with nonresponse. This last requirement was critical. Because noncompletion of the core and main task booklets was correlated with ability, background information about nonrespondents was needed in order to impute cognitive data for these persons.

IALS countries were instructed to obtain at least a background questionnaire from sampled individuals. All countries participating in IALS instructed interviewers to make callbacks at households that were difficult to contact.

In general, the survey was carried out in the national language. In Canada, respondents were given a choice of English or French, and in Switzerland, samples drawn from French-speaking and German-speaking cantons were required to respond in those respective languages. When respondents could not speak the designated language, attempts were made to complete the background questionnaire so that their literacy level could be estimated and the possibility of distorted results would be reduced. In the United States, the test was given in English, but a Spanish version of the background questionnaire and bilingual interviewers were available to assist individuals whose native language was not English.

Survey respondents spent approximately 20 minutes answering a common set of background questions concerning their demographic characteristics, educational experiences, labor market experiences, and literacy-related activities. Responses to these background questions made it possible to summarize the survey results using an array of descriptive variables, and also increased the accuracy of the proficiency estimates for various subpopulations. After answering the background questions, the remainder of respondents’ time was spent completing a booklet of literacy tasks designed to measure their prose, document, and quantitative skills. Most of these tasks were open-ended, requiring respondents to provide a written answer.

In the United States, the IALS interview period was from October to November 1994. IALS was conducted by 149 Census Bureau interviewers. All of them had at least 5 days of interviewer training. They were given a one-day training on IALS and were provided with substantial training and reference materials based on the Canadian training package. They also performed a day of field training under the supervision of a regional office supervisor. Each interviewer had an average workload of 33 interviews, and the average number of response interviews per interviewer was 21. They were supervised by six regional supervisors who reviewed and commented on their work.

Before data collection, a letter was sent to the selected addresses describing the upcoming survey. The survey was limited to 90 minutes. If a respondent took more than 20 minutes per block, the interviewer was instructed to move the respondent on to the next block.


Data processing. As a condition of their participation in IALS, countries were required to capture and process their files using procedures that ensured logical consistency and acceptable levels of data capture error. Specifically, countries were advised to conduct complete verification of the captured scores (i.e., enter each record twice) in order to minimize error rates. One hundred percent keystroke validation was needed. Specific details about scoring are provided in a separate section below.

To create a workable comparative analysis, each IALS country was required to map its national dataset into a highly structured, standardized record layout. In addition to specifying the position, format, and length of each field, this International Record Layout included a description of each variable and indicated the categories and codes to be provided for that variable. Upon receiving a country’s file, Statistics Canada performed a series of range checks to ensure compliance to the prescribed format. When anomalies were detected, countries corrected the problems and submitted new files. Statistics Canada did not, however, perform any logic or flow edits, as it was assumed that participating countries performed this step themselves.

Editing. Most countries followed IALS guidelines, verifying 100 percent of their data capture operation. The two countries that did not comply with this recommendation conducted sample verifications, one country at 20 percent and the other at 10 percent. Each country coded and edited its own data, mapping its national dataset into the detailed International Record Layout, which included a description of each variable and indicated the categories and codes to be provided for that variable. Industry, occupation, and education were coded using the standard international coding schemes: the International Standard Industrial Classification (ISIC), the International Standard Classification of Occupations (ISCO), and the International Standard Classification of Education (ISCED). Coding schemes were provided for open-ended items; the coding schemes came with specific instructions so that coding error could be contained to acceptable levels.


Scoring. Respondents’ literacy proficiencies were estimated based on their performance on the cognitive tasks administered in the assessment. Because the open-ended items used in IALS elicited a large variety of responses, responses had to be grouped in order to summarize the performance results. As they were scored, responses to IALS open-ended items were classified as correct, incorrect, or omitted. The models employed to estimate ability and difficulty were predicated on the assumption that the scoring rubrics developed for the assessment were applied in a consistent fashion within and between countries. To reinforce the importance of consistent scoring, a meeting of national study managers and chief scorers was held prior to the commencement of scoring for the main study. The group spent 2 days reviewing the scoring rubrics for all the survey items. Where this review uncovered ambiguities and situations not covered by the guides, clarifications were agreed to collectively, and these clarifications were then incorporated into the final rubrics. To provide ongoing support during the scoring process, Statistics Canada and ETS maintained a joint scoring hotline. Any scoring problems encountered by chief scorers were resolved by this group, and decisions were forwarded to all national study managers. Study managers conducted intensive scoring training using the scoring manual and discussed unusual responses with scorers. They also offered additional training to some scorers, as needed, to raise their accuracy to the level achieved by other scorers.

To maintain coding quality within acceptable levels of error, each country undertook to rescore a minimum of 10 percent of all assessments. Where significant problems were encountered, larger samples of a particular scorer’s work were to be reviewed and, where necessary, their entire assignments rescored. Countries were not required to resolve contradictory scores in the main survey (as they had been in the pilot), since outgoing agreement rates were far above minimum acceptable tolerances.

Since there could still be significant differences in the consistency of scoring between countries, countries agreed to exchange at least 300 randomly selected booklets with another country sharing the same test language. In all cases where serious discrepancies were identified, countries were required to rescore entire items or discrepant code pairs.

Intra-country rescoring. A variable sampling ratio procedure was set up to monitor scoring accuracy. At the beginning of scoring, almost all responses were rescored to identify inaccurate scorers and to detect unique or difficult responses that were not covered in the scoring manual. After a satisfactory level of accuracy was achieved, the rescoring ratio was dropped to a maintenance level to monitor the accuracy of all scorers. Average agreements were calculated across all items. Precautions were taken to ensure that the first and second scores were truly independent.

Intercountry rescoring. To determine intercountry scoring reliabilities for each item, the responses of a subset of examinees were scored by two separate groups. Usually, these scoring groups were from different countries. Intercountry score reliabilities were calculated by Statistics Canada, and then evaluated by ETS. Based on the evaluation, every country was required to introduce a few minor changes in scoring procedures. In some cases, ambiguous instructions in the scoring manual were found to be causing erroneous interpretations and therefore lower reliabilities.

Using the intercountry score reliabilities, researchers could identify poorly constructed items, ambiguous scoring criteria, erroneous translations of items or scoring criteria, erroneous printing of items or scoring criteria, scorer inaccuracies, and, most important, situations in which one country consistently scored differently from another. In the latter circumstance, scorers in one country may consistently rate a certain response as being correct while those in another country score the same response as incorrect. ETS and Statistics Canada examined scoring carefully to identify situations in which scorers in one country were consistently rating a certain response as being correct while those in another country were scoring the same response as incorrect. Where a systematic error was identified in a particular country, the original scores for that item were corrected for the entire sample. 


Estimation Methods

Weighting was used in the 1994 IALS to adjust for sampling and nonresponse. Responses to the literacy tasks were scored using IRT scaling. A multiple imputation procedure based on plausible values methodology was used to estimate the literacy proficiencies of individuals who completed literacy tasks.

Weighting. IALS countries used different methods for weighting their samples. Countries with known probabilities of selection could calculate a base weight using the probability of selection. To adjust for unit nonresponse, all countries poststratified their data to known population counts, and a comparison of the distribution of the age and sex characteristics of the actual and weighted samples indicates that the samples were comparable to the overall populations of IALS countries. Another commonly used approach was to weight survey data to adjust the rough estimates produced by the sample to match known population counts from sources external to IALS. This “benchmarking” procedure assumes that the characteristics of nonrespondents are similar to those of respondents. It is most effective when the variables used for benchmarking are strongly correlated with the characteristic of interest—in this case, literacy levels. For IALS, the key benchmarking variables were age, employment status, and education. All of the IALS countries benchmarked to at least one of these variables. The United States used education.

Weights for the U.S. IALS sample included two components. The first assigned weights to CPS respondents, and the second assigned weights to IALS respondents.

The CPS weighting scheme was a complex one involving three components: basic weighting, noninterview adjustment, and ratio adjustment. The basic weighting compensated for unequal selection probabilities. The noninterview adjustment compensated for nonresponse within weighting cells created by clusters of PSUs of similar size; Metropolitan Statistical Area (MSA) clusters were subdivided into central city areas, and the balance of the MSA and non-MSA clusters were divided into urban and rural areas. The ratio adjustment made the weighted sample distributions conform to known distributions on such characteristics as age, race, Hispanic origin, sex, and residence.

The weights of persons sampled for IALS were adjusted to compensate for the use of the four rotation groups, the sampling of the 60 PSUs, and the sampling of persons within the 60 PSUs. The IALS noninterview adjustment compensated for sampled persons for whom no information was obtained because they were absent, refused to participate, had a short-term illness, had moved, or had experienced an unusual circumstance that prevented them from being interviewed. Finally, the IALS ratio adjustment ensured that the weighted sample distributions across a number of education groups conformed to March 1994 CPS estimates of these numbers.


Scaling. The scaling model used in IALS was the two-parameter logistic model based on IRT.

Items developed for IALS were based on the framework used in three previous large-scale assessments: the Young Adult Literacy Assessment, the DOL survey, and the National Adult Literacy Survey. As a result, IALS items shared the same characteristics as the items in these earlier surveys. The English versions of IALS items were reviewed and tested to determine whether they fit into the literacy scales in accordance with the theory and whether they were consistent with the National Adult Literacy Survey data. Quality control procedures for item translation, scoring, and scaling followed the same procedures used in the National Adult Literacy Survey and extended the methods used in other international studies.

Identical item calibration procedures were carried out separately for each of the three literacy scales: prose, document, and quantitative literacy. Using a modified version of Mislevy and Bock’s 1982 BILOG computer program—see BILOG: Item analysis and test scoring with binary logistic models, Scientific Software—the two-parameter logistic IRT model was fit to each item using sample weights. BILOG procedures are based on an extension of the marginal-maximum-likelihood approach described by Bock and Aitkin in their 1981 Psychometrika article, “Marginal maximum likelihood estimation of item parameters: An application of an EM algorithm.”

Most of the items administered in IALS were successful from a psychometric standpoint. However, despite stringent efforts at quality control, some of the assessment items did not meet the criteria for inclusion in the final tabulation of results. Specifically, in carrying out the IRT modeling used to create the three literacy scales, researchers found that a number of assessment items had significantly different item parameters across IALS countries.


Imputation. A respondent had to complete the back-ground questionnaire, pass the core block of literacy tasks, and attempt at least five tasks per literacy scale in order for researchers to be able to estimate his or her literacy skills directly. Literacy proficiency data were imputed for individuals who failed or refused to perform the core literacy tasks and for those who passed the core block but did not attempt at least five tasks per literacy scale. Because the model used to impute literacy estimates for nonrespondents relied on a full set of responses to the background questions, IALS countries were instructed to obtain at least a background questionnaire from sampled individuals. IALS countries were also given a detailed nonresponse classification to use in the survey.

Literacy proficiencies of respondents were estimated using a multiple imputation procedure based on plausible values methodology. Special procedures were used to impute missing cognitive data.

Literary proficiency estimation (plausible values). A multiple imputation procedure based on plausible values methodology was used to estimate respondents’ literacy proficiency in the 1994 IALS. When a sampled individual decided to stop the assessment, the interviewer used a standardized nonresponse coding procedure to record the reason why the person was stopping. This information was used to classify nonrespondents into two groups: (1) those who stopped the assessment for literacy-related reasons (e.g., language difficulty, mental disability, or reading difficulty not related to a physical disability); and (2) those who stopped for reasons unrelated to literacy (e.g., physical disability or refusal). About 45 percent of the individuals did not complete the assessment for reasons related to their literacy skills; the other respondents gave no reason for stopping or gave reasons unrelated to their literacy.

When individuals cited a literacy-related reason for not completing the cognitive items, it implies that they were unable to respond to the items. On the other hand, citing reasons unrelated to literacy implies nothing about a person’s literacy proficiency. Based on these interpretations, IALS adapted a procedure originally developed for the National Adult Literacy Survey to treat cases in which an individual responded to fewer than five items per literacy scale, as follows: (1) if the individual cited a literacy-related reason for not completing the assessment, then all consecutively missing responses at the end of the block of items were treated as wrong; and (2) if the individual cited reasons unrelated to literacy for not completing the assessment, then all consecutively missing responses at the end of a block were treated as “not reached.”

Proficiency values were estimated based on respondents’ answers to the background questions and the cognitive items. As an intermediate step, the functional relationship between these two sets of information was calculated, and this function was used to obtain unbiased proficiency estimates with reduced error variance. A respondent’s proficiency was calculated from a posterior distribution that was the multiple of two functions: a conditional distribution of proficiency, given responses to the background questions; and a likelihood function of proficiency, given responses to the cognitive items. 

Recent Changes

Since IALS was a one-time assessment, there are no changes to report.


There are no plans to conduct IALS again. However, a new survey, the Adult Literacy and Lifeskills Survey (ALL), was administered in 2003 (see ALL chapter). The aspects of this survey that address literacy were built on methodologies used in IALS.