The relevant bit from the paper, emphasis mine: > Cross-sectional data with retrospective indicators of scholarly culture are affected by measurement error and

The relevant bit from the paper, emphasis mine: > Cross-sectional data with retrospective indicators of scholarly culture are affected by measurement error and indicators could reflect unmeasured influence of other confounding variables which may lead to over-optimistic estimates (de Vries and de Graaf, 2008). However, prior research using longitudinal data from Australia with corrections for measurement error showed that a substantial impact of home library size on adult education existed net of the effects of academic ability (IQ) of adults or their father's scholarly habits (i.e. employment in occupations where use of books is common) as well as family income or wealth (Evans et al., 2010). Although we have no means of correcting for these potential biases in ways available in longitudinal data, we argue that even somewhat optimistic estimates are of value as an initial step in proposing and assessing hypotheses for future, more stringent tests. To limit the potential for confounding adolescent and adult literacy-enhancing activities, we control for adult out-of-work activities related to literacy, numeracy and ICT skills that might correlate with scholarly culture experienced in adolescence but are indicators of adult scholarly culture.