households by consumption than by the asset index. For example, in the case of child immunizations, when we rank households by consumption, the bottom quintile accounts for 21.4 percent of all immunizations, compared to 18.3 percent by the top quintile. If, instead, we rank households by the asset index, the bottom quintile accounts for only 9.6 percent of immunizations, compared to 32.1 percent by the top quintile. Put differently, the immunization rates range from 18.5 (bottom quintile) to 70.4 percent (top quintile) when we measure welfare by the asset index, indicating considerable inequality. Similar differences can be found for the other health service indicators, with the notable exception of health center visits. In this case, utilization is more equal when households are ranked by the asset index. The reasons for this seeming anomaly is discussed further below.

This pattern is also reflected in the concentration curves of appendix figures 1 to 5. In order to assess the extent and significance of differences in inequality, we can look at the concentration index for the different services. These are reported in Table 2. The results broadly confirm the observations above, and offer some statistical corroboration. In the case of consumption as welfare measure, the concentration index indicates statistically significant inequality in favor of richer households for all services. With households ranked by the asset index rather than consumption, the inequality is greater for all services except health center visits, for which the concentration index indicates inequality in utilization in favor of poorer households. The differences between the two concentration indices are significant for all services.

**Table 2. Concentration Indices**

||**Consu**<br>|**mption**<br>|**Asset**<br>|**index**<br>|**Difference**<br>**CI - CI**|**t-value for**<br>**difference**|
|---|---|---|---|---|---|---|
||**CI**|**t-value**|**CI**|**t-value**|**C AI**||
|Hospital visits|0.166|8.72|0.231|12.94|-0.065|-3.35|
|Health center visits|0.066|3.85|-0.136|-8.49|0.202|9.99|
|Complete<br>immunizations|0.059|8.35|0.194|34.69|-0.135|-19.1|
|Delivery control|0.063|11.86|0.154|35.01|-0.091|-15.27|
|Institutional delivery|0.089|11.31|0.266|43.26|-0.176|-20.06|

Hence, it is clear that our conclusions about the degree of socioeconomic inequality in health service use depend in important ways on our choice of welfare indicator. If we address this question using consumption as a measure of socioeconomic status we conclude that although there is some inequality in service use, the inequality is quite moderate for all services. If, in contrast, we use the asset index as a measure of SES, the distribution of service use by socioeconomic status appears far less sanguine. These findings are of some interest in their own right, but they also beg the question of what is driving the observed differences

# **_What explains the observed differences?_**

As was discussed above, changes in the concentration index as we change the ranking variable are related to the correlation between the health service variable ( _hi_ ) and the change in individual ranking (∆ _Ri_ ) that results from re-ranking individuals using the alternative welfare measure. In the case of the Mozambique IAF, the Spearman rank 12