The most accurate method would be to use the ungrouped ethnicity so that the researcher can apply the same approach to all surveys, or at least for the 2003 NDHS. I am not sure if the ten ethnic groups from 2008 and 2013 are the same. If they are, the easiest approach to standardize the ethnicity across all three surveys is to use the six main groups from 2003 and place combine Igala, Ibibio, Ijaw, and Ekoi into the "other" group. I think the latter is the best approach because the percentages for the other ethnic groups are so small.

I believe that NPopC developed a more extensive list of ethnicities captured in their other surveys at the time of the 2008 NDHS. I believe the same list was used for the 2013 NDHS.

Variable V131 in the recode data file has all the individual ethnic categories as they were collected in the field. In the final report, Mianmian (who produced most chapters for NDHS 2013) have specific individual categories displayed in the ethnic variable without grouping (in green below), missing displayed as missing (in orange below), and the rest of the categories grouped as "Others (in red below)".


Best,
Claudia