To calculate the average score in adult literacy proficiency from the STEP surveys we have:

Calculated the mean literacy score for each individual in the survey (over 10 plausible value scores)

Taken the sum of the mean literacy scores over all individuals

Divided the aggregate literacy score by the number of individuals

The STEP data for calculated average adult literacy (8 additional observations) is appended to the PIAAC scores from World Bank EdStats dataset.

8 STEP observations include: Armenia (2013); Bolivia (2012); Colombia (2012); Georgia (2013); Ghana (2013); Kenya (2013); Ukraine (2012); and Vietnam (2012)

As the STEP methodology note outlines "The STEP literacy assessment has been developed specifically for use in the context of developing countries, and it includes sets of questions taken from PIAAC, the International Adult Literacy Survey, and the Adult Literacy and Life Skills Survey. This overlap allows countries participating in the STEP program to compare their literacy results with those of over 30 other countries."

Full citation: “Pierre, Gaelle; Sanchez Puerta, Maria Laura; Valerio, Alexandria; Rajadel, Tania. 2014. STEP Skills Measurement Surveys : Innovative Tools for Assessing Skills. Social protection and labor discussion paper;no. 1421. World Bank Group, Washington, DC. © World Bank. https://openknowledge.worldbank.org/handle/10986/19985 License: CC BY 3.0 IGO.”

Sources

Data Published By: World Bank EdStats and the World Bank Central Microdata Catalog

Data publisher source:OECD Programme for the International Assessment of Adult Competencies (PIAAC) using survey data

Link: PIAAC: https://data.worldbank.org/data-catalog/ed-stats and STEP: http://microdata.worldbank.org/index.php/catalog/step