One striking feature of both Figure 1 and 2 is ihe high level and odd pattern to the estimates derived from the ICDS. Hill and others (1'999) noted this in their analysis of trends in child mortality in Vietnam, and decided in the event to discard the ICDS-based estimates. The 1989 Census also gives some rather implausible numbers for the 25-29 and 30-34 age groups. The other estimates give a clear picture of declining infant and under-five mortality rates with little sign of any stagnation in recent years. There is clearly some uncertainty, however, over the actual levels of infant and under-five mortality. The DHS and VLSS give very similar rates-around 30%o and 40%o for infant and under-five mortality, respectively, in 1995. These figures are precisely the same as the consolidated estimates reported by Hill and others for that year. The reason for the higher MICS figures is unclear. The authors of the Census argued that the rates implied by the raw Census data (those reported here) were too low since the Census appeared to have caused an underreporting of deaths in the previous year. They used the results from a post-enumeration survey to "correct" the mortality rates, concluding that the IMR for Vietnam was probably around 37%o rather than the figure of 25%o or so implied by the crude data (Central Census Steering Committee 2000). It has to be said it is unclear why the Census should be any more prone to this difficulty than any of the other sources, and why any such underreporting should lead to such a large upward adjustment.

# **_Direct estimates of infant and under-five mortality in Vietnam_**

The mechanics of the direct method are illustrated in Table 1 for data from the 1998 VLSS, where for the purpose of the table children born in the previous ten years were included. This resulted in 5,316 children being selected. The first row of column 4 indicates that 195 children were "withdrawn" during the first six months (the interval used in this example), meaning that 195 children were born within the six months before the survey and therefore had less than six months of exposure. The assumption is that these 195 children were, on average, exposed for only half of the six months,<sup>4</sup> so that the total number of children exposed during the first six months was 5,316 less half of 195, or 5219 (column 5). Of the 5,316 born during the previous ten years, 114 died during the first six months, so that the proportion surviving was (5,219 - 114)/5,219, or 0.9782. The mortality rate for the first six months, 0.5qo, is equal to (1 - 0.9782) x 1,000, or 21.8 per 1,000 births. The number of children starting the second six months is 5,316 - 195 - 114, or 5,007. Of these 159 are exposed less than six months-i.e., were born less than one year before the survey. Of the 4,928 children exposed to the risk of death in the second half of their first year of life, 15 died before their first birthday, giving a cumulative

> It is because of this assumption that the choice of interval widih matters. The mortality rates reported below are, in fact, obtained using non-fixed intervals, with smaller intervals for the first year of life than later years. This is easily accomplished within the computer program Stata.

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