All statistics are computed using sampling weights.
Estimation of standard errors for significance testing are computed by making use of:
- Replication methods (jackknife repeated replication, JK2 variant) to estimate sampling variance
- Ten plausible values for estimating measurement variance.
General note: PIAAC data are designed for group-level reporting, and adults’ scale scores in the database are not intended to report performance of individual students’ or very small groups.
For doing secondary analyses, the following tools have been designed to help SAS, Stata, or SPSS users explore the data and compute statistics:
- PIAAC_TOOL SAS Macro
- STATA Respest Macro
- IEA IDB Analyzer
- PIAAC Data Explorer (based on the International Data Explorer)
These tools take into account the characteristics of the sampling and assessment design, implement the corresponding replication method, and make use of existing plausible values.
One data file for each country with background questionnaires, all derived variables and scales, achievement responses to assessment items (and timing) and scores.
Responses to all items used in the assessment are included in the database. After each cycle, however, some of the items are released to the public for informational purposes. The remaining items are kept secure, thus ensuring the possibility of measuring trends over time. Note that the response data to all items used in the assessment is publicly available in the data files.