# **Comparability** in **the method of** estimating **purchased food expenditure**

Both the 1993 and 1995 surveys use the same method of estimating food expenditure, which essentially involves multiplying the estimate of purchases made over the last month for each month by the number of months the commodity is declared to be purchased. The drawback of this method is that it underestimates annual food purchases for the sample as a whole, since it makes no correction for the households that did not purchase the commodity in the previous month, but do purchase it during other months of the year. Typically surveys deal with this problem by multiplying purchases made during the previous month by 12 months, rather than by the declared number of months. Multiplying by 12 months yields a correct sample mean under various assumptions (see Appendix B). When the survey is not conducted over the course of the year, and there is a variation across the months of the year in the number of households reporting zero purchases the last month, the procedure of multiplying by 12 will not necessarily yield the mean-preserving result. However, it may still be a better estimate than the one produced by multiplying by the declared number of months.

We re-estimated purchased food expenditures by multiplying by 12 months instead of multiplying by the declared number of months, recomputed total household expenditure, and applied the seasonal correction parameters as described in the section above to the total expenditure aggregate. Because in 1995 food expenditures are much higher using the annualized rather than declared months method, poverty estimates are correspondingly lower in 1995 and thus the increase in poverty between 1993 and 1995 smaller (table 28). The difference between the annualized and the declared months method is particularly large in the case of East Forest and the Savannah, because of the large number of observations from households that do not purchase food during the entire year.

**Table 28 Comparison of the Seasonally Adjusted Headcount Index of Poverty Based on the Annualized Monthly and the Declared Months * Monthly Value Estimates of Purchased Food Expenditure for 1993 and 1995**

||_Annualize_<br>_purchas_<br>_expenditu_|_Headcount I_<br>_d monthly_<br>_edfood_<br>_re estimate_|_ndex of Poverty_<br>_Declared months * monthly_<br>_value purchasedfood_<br>_expenditure estimate_|
|---|---|---|---|
|_Region_|_1993_|_1995_|_1993_<br>_1995_|
|Abidjan|.040|.192|.051<br>.202|
|Other Cities|.291|.249|.293<br>.275|
|East Forest|.376|.307|.392<br>.383|
|West Forest|.390|.503|.393<br>.532|
|Savannah|.506|.432|.510<br>.509|
|Cote d'Ivoire|.316|.323|.323<br>.367|

The decision about which aggregate to use for estimating purchased food expenditures in 1993 and 1995 is not clear-cut, however. If, for example, for seasonal or other reasons, the percentage of households with zero purchases the previous month but positive purchases at some point during the year is less that what would be expected given the average number of months of reported expenditure (assuming no recall bias), then the annualized method would overestimate expenditure. Appendix B describes some of the drawbacks of the two methods.

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