However, beliefs about the legitimacy of the economic system are clearly analogous to just world beliefs in the economic domain, and the ISJP included four items that can be used a s indicators of such a belief.
The data for the International Social Justice Project (ISJP) were collected in 1991, using trained interviewers and a questionnaire based upon an agreed English language version (translated where necessary).
For the present analyses, the original response scale given for each of the selected items in the ISJP codebook (Alwin, Klingel and Dielman, 1993) was reversed.
The ISJP obtained direct empirical measures of all three of the main observable quantities identified by justice theory -- the actual reward, the just reward, and the expressed justice evaluation -- for the respondent him- or herself (the reflexive case).
This variable is measured by the response to the ISJP question, "Do you think you were paid much less than you deserved, somewhat less than you deserved, about what you deserved, somewhat more than you deserved, or much more than you deserved?" The five response categories were coded -2 to +2, with zero as the point of perfect justice.
The ISJP collected information on respondent's actual job income.
If a respondent provided both (i) an actual job income and (ii) a justice evaluation of perfect justice, the ISJP set the just job income equal to the actual job income.
 The ISJP data make it possible to construct several versions of the experienced justice evaluation, taking into account different features of the data.
Third, we compare the actual and just earnings equations; ISJP data make it possible, for the first time, to carry out these comparisons.
The ISJP data provide a rare opportunity to compare the gender gap in actual earnings with that in just earnings.
However, it is evident that the information they provide will enable more refined specification of models for subsequent research, models which carefully incorporate features of the economic and cultural climate in each country at the time of the ISJP interviews.