Using the wealth index for each country in the pooled regression would indicate relative position in that country. Calculating a wealth index from the pooled data set is problematic in a couple of areas: A common lower set of variables would need to be used losing some information. Yes, one country could be at the low end and other at the high end. An alternative would be to use the Comparative Wealth Index but the second problem would still remain if the countries are much different from each other. The Comparative Wealth Index allows the wealth for each household to be comparable to that of households in other countries that have the same score.