Dear StataList,

I am reading an interesting paper by Brons et al. (2017), where on page 812 they describe how they summarised parental SES into a single index from ESS-9. Here is the excerpt:

"Detailed country-specific information was available in the ESS on the highest level of educational attainment for both parents. This information was converted into the International Standard Level of Education (ISLED), a recently developed comparative measure of educational level. Likewise, father’s and mother’s occupation when the respondent was 14 years old are measured in the International Standard Classification of Occupation (ISCO-88), and converted into the International Socio-Economic Index of occupational status (ISEI). A principal component analysis indicated that the four indicators of educational and occupational status of the parents can be summarized into a single index with high reliability (Cronbach’s = 0.85 for all countries pooled). The index was constructed after standardizing and averaging the four indicators. An average score was calculated jointly for both parents because we are interested in the overall effect of parents’ SES rather than to what extent fathers or mothers are more influential. This parental SES index was again standardized to a Z-metric (mean = 0, SD = 1) within countries, so that the effects of this variable in all countries refer to a unit SD."

I am trying to do the same but using the ESS-9 (2018). I am not sure what I am doing wrong; however, after removing missings and recoding father's/mother's educational and occupational scale on the same scale, my Cronbach alpha on the four items is slightly over 0.4, which is certainly not enough for building a single index. Could someone please advise on how to do things correctly here?

Thank you very much in advance.