Research on educational inequalities, as well as social stratification research in general, has since long conceptualized and operationalized social origins using parental status, in particular their occupational position and/or educational achievement. The theoretical rationale is that an individual’s social position depends on his/her household. As a matter of fact, often in actual research practice only paternal characteristics have been used, either on theoretical grounds or using the so-called “dominance” coding. Such a practice is not tenable today, when women systematically outperform men in educational achievement and where their labour market partecipation has dramatically raised. The paper shows how father-based and single-parent codings systematically bias the estimates of inequality of educational opportunities (IEO), particularly concerning its trend over time. It studies systematically how different codings of social origins, by including or excluding relevant information, change the empirical results of models of IEO for the Italian case. It uses survey data from three waves (1998, 2003 and 2008) of the MultiPurpose Survey carried out by the Italian National Institute for Statistics (Istat), in order to compare the fit and the parameters estimates for the association between parental education and educational achievement of a set of logit models of IEO and of its trend over time, where different measurement strategies of social origin, as indexed by parental education, are used. This is done for two school transitions, namely achieving at least upper secondary and achieving tertiary, including all post-secondary titles. We also compare the magnitude of the effect of parental social class and education, confirming the latter to be stronger than the former. Results show that models where social origin is measured including information concerning both parents reproduce the data better than models relying on one parent only. The dominance approach underestimates the association between parental education and respondent's education when parents have a similar educational title, while it overestimates it when a wider education gap is found between parents. In particular, a “full interaction” coding, exploiting all available information by considering all combinations of maternal and paternal education, provides the best fit for models of the transition to upper secondary education, while concerning the transition to a tertiary title the “reduced interaction” coding, which does not consider the dominant parent in non-homogamic parental couples, is statistically equivalent to the full interaction one. Our analysis shows that including both parents significantly changes the resulting evidence concerning the trend of IEO over cohorts: models using the interacted coding of social origin, exploiting all available information, show a clearer picture of a declining IEO over time, this decrease being mostly determined by the offspring of low-educated parents and of those parental couples where the maternal educational level is dominant with respect to the paternal one.

关于教育不平等的研究以及一般的社会分层研究，长期以来一直利用父母身份，特别是父母的职业地位和/或教育成就，对社会出身进行概念化和实用化。从理论上讲，一个人的社会地位取决于他/她的家庭。事实上，无论是在理论上还是在所谓的“主导性”编码上，通常在实际的研究实践中仅使用了父系特征。如今，当女性在教育成就上系统地胜过男性，并且劳动力市场的参与度显着提高时，这种做法今天仍然站不住脚。本文说明了基于父亲的编码和单亲编码如何系统地偏向对教育机会不平等（IEO）的估计，特别是关于其随着时间的趋势。它通过包括或排除相关信息，系统地研究了社会起源的不同编码如何改变意大利案例的IEO模型的经验结果。它使用来自意大利国家统计局（Istat）的三阶段（1998、2003和2008）多用途调查的调查数据，以比较适合度和参数估计，以评估父母教育与教育成就之间的关联IEO的一组logit模型及其随时间的趋势，其中使用了由父母教育索引的不同的社会出身测量策略。这是针对两个学校的过渡而完成的，即至少达到高中和达到高等教育，包括所有中学后的头衔。我们还比较了父母社会阶层和教育的影响程度，证实了后者比前者更强。结果表明，与仅依靠一个父母的模型相比，在测量包括两个父母的信息在内的社会出身的模型时，其数据再现效果更好。当父母具有相似的学历时，优势法低估了父母教育与受访者的教育之间的联系，而当父母之间存在更大的教育鸿沟时，优势法则高估了这种联系。特别是，通过考虑母婴教育的所有组合来利用所有可用信息的“完全互动”编码，最适合于过渡到高中教育的模型，在涉及过渡到第三级头衔时，“减少的互动”编码在统计学上等同于完整的互动，该编码不考虑非同源父母对中的主要父母。我们的分析表明，包括父母双方在内，都会显着改变与群体有关的IEO趋势的证据：使用社会起源的交互编码的模型，利用所有可用信息，显示随着时间的推移IEO下降的更清晰图片，这一下降主要是由确定的由低学历的父母和父母对子女的教育水平占主导地位的父母对子女的后代。