# Index of cognitive skills and educational attainment

#### Z-score (number of standard deviations above or below the mean)

**Group 5**

less than -1.0**Group 4**

between -1.0 and -0.5**Group 3**

between -0.5 and 0.5**Group 2**

between 0.5 and 1.0**Group 1**

more than 1.0

The Index was first published in November 2012, and updated with the latest data in January 2014. The 2014 Index follows the same methodology as the original Index. No countries have been added or removed; the indicators, weightings and sources remain the same.

The Global Index of Cognitive Skills and Educational Attainment compares the performance of 39 countries and one region (Hong Kong) on two categories of education: Cognitive Skills and Educational Attainment. The Index provides a snapshot of the relative performance of countries based on their education outputs.

The indicators used in this Index are:

- Cognitive Skills: PISA, TIMSS and PIRLS scores in Reading, Maths and Science

- Educational Attainment: literacy and graduation rates

**How is the Index calculated?**

The overall index score is the weighted sum of the underlying two category scores. Likewise, the category scores are the weighted sum of the underlying indicator scores (see below for the default weights applied). Each indicator score is calculated on the basis of a z-score normalisation process. This process enables the comparison and aggregation of different data sets (on different scales), and the scoring of countries on the basis of their comparative performance.

**What is a z-score?**

A z-score indicates how many standard deviations an observation is above or below the mean. To compute the z-score, the EIU first calculated each indicator’s mean and standard deviation using the data for the countries in the Index, and then the distance of the observation from the mean in terms of standard deviations.

**How are the categories and indicators weighted?**

The overall index score is the weighted sum of the underlying two category scores. Likewise, the category scores are the weighted sum of the underlying indicator scores. The default weighting for the Index is two-thirds to cognitive skills and one-third to educational attainment. Within the cognitive skills category, the Grade 8 tests’ score accounts for 60% while the Grade 4 tests’ score accounts for 40% (Reading, Maths and Science all account for equal weights). Within the educational attainment category, the literacy rate and graduation rates account for equal weights.

When making comparisons of individual countries across Index versions it is important to focus on the ranking rather than the score. This is because the mean and standard deviation for each indicator are specific to each version of the Index and the sample of countries.

The data within the 2014 Index was collected and/or calculated in September 2014, while the data within the 2012 Index was collected and/or calculated in September 2012. For the full methodology for the 2014 Index please refer to the Appendix 2 in the latest report; for more details on the Learning Curve’s quantitative component, please refer to Appendix 1 in The Learning Curve 2012 Report.