# Seasonality

The 1993 and 1995 surveys were conducted only over a period of several months: June to November 1993 and April and May 1995. Households were interviewed once during that period, and were asked about expenditures over the past week, month, three months or year depending on the category of expenditure. If either of these surveys were conducted during periods of exceptionally low or high expenditure, then the estimates of mean expenditure and the poverty incidence calculations could be biased. To assess whether there is a bias, we need some way of determining how expenditure varies over the year and correcting for seasonal fluctuations. Fortunately the 1985-1988 CILSS surveys can be used for this purpose.

Households in the CILSS surveys were interviewed once about their expenditures, with the interviews conducted randomly throughout the year. Since the CILSS surveys had a two week recall period for both purchased food and many nonfood items, a high percentage of expenditure would potentially be subject to seasonal variation. This variation in expenditure could arise from seasonal fluctuations prices, particularly food prices, that are not offset by variations in quantity, or to seasonal variation in income, to the extent that households do not smooth their consumption over the course of a year. There could also be seasonal variation present in the estimate of expenditure on items for which the recall period was a year if the period of the year during which the interview takes place influences the size of the recall error. For example, households interviewed during a period in which they typically purchase more durable goods, send more remittances, or consume more home production might remember more of their expenditures than households interviewed during other periods of the year. Or the value households attach to the consumption of home production may vary with the market price of the home-consumed product. Or the estimate of the quantity consumed each day or the number of days per month a home-produced good is consumed may reflect the pattern during the month that household is interviewed rather than the average over the year.<sup>23</sup> Thus any seasonal variation evident in the surveys could reflect genuine seasonal variation in expenditure as well as systematic seasonal recall biases.

To assess the extent of seasonal variation, we regressed the log of household expenditure on dummy variables for the season during which the household was interviewed as well as on a set of variables included to control for possible non-randomness in the distribution of households across months of the year, including household size, the square of household size, and dummy variables for education levels. To determine whether there were region-specific seasonal interactions, a set of regional dummies was then interacted with dummy variables for three time periods during year: April/May, correspondingly to the 1995 survey; June-November, corresponding to the 1993 survey, and December-March, the remaining months. Imposing the restriction that the sum of the three time period 23 To examine whether there was any seasonality present in the annual estimate of consumption of home production, we regressed the annual estimate of consumption of home production (for those households reporting positive home consumption) on the region and crop dummy variables interacted with the time period variables. The June-November time period was split into two sub-periods: June-August, and September -November, corresponding more closely to the pre and post-harvest periods. In the regression over the sample of households with expenditures less than or equal to 100,000 CFAF per capita, only the East Forest*June-August dummy is significant at the 5 percent level, indicating that expenditures among East Forest non export crop farmers are significantly lower than the December-March period. Over the much larger sample of households whose expenditur **e** xceeds 100,000 CFAF per capita, the Other Cities, East Forest, West Forest and Savannah JuneAugust dummies are significant and negative. This suggests that the time of the year during which the interview biases the estimate of consumption of home production.

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