ease, and those that examine the cost-effectiveness of interventions aimed at preventing or controlling the disease.

The Economic Costs of Malaria

The primary cost of malaria is its contribution to mortality and morbidity. Because precise data on morbidity and mortality are often lacking, it is not surprising that estimates of the disease's economic impact are vague and imprecise. A number of factors make calculating economic impact very difficult. For one, the disease affects each geographic region, and the individual communities within them, differently. The economic impact of malaria-related death also varies according to the age of those who die. In Africa and other highly endemic regions, where most deaths are among infants and young children, the impact on productivity is lower than in areas of low to moderate endemicity, where the burden of disease falls primarily on adults, who are the main breadwinners or primary caretakers (Over et al., 1990).

Most economic impact studies attempt to measure the effects of episodes of malarial illness on lowered worker productivity, a literature reviewed by Barlow and Grobar (1986). Researchers have estimated that each case of malaria causes between 5 and 20 days of disability (Van Dine, 1916; Russell and Menon, 1942; Malik, 1966; Conly, 1975). A common convention in the literature has been to use seven days of work lost per bout of malaria whenever this parameter is needed to assess a program and cannot be independently estimated (Sinton, 1935, 1936; Quo, 1959; San Pedro, 1967-1968; Niazi, 1969).

A number of studies have attempted to measure malaria's impact on worker output. One study found that malaria prevalence did have an effect on rice production (Audibert, 1986) and another that found farm families with malaria cleared 60 percent less land than did families free of the disease (Bhombore et al., 1952).

Other researchers have shown that in agricultural settings malaria can influence the choice of crops. Conly (1975) observed that farmers replaced higher-value crops, whose growing season coincided with the peak malaria season, with lower-value crops with different growing seasons. A similar analysis revealed that new settlers in agricultural areas may decide, a priori, to plant crops that are less sensitive to interruptions in cultivation (e.g., root crops) to avoid the potential impact of malaria (Rosenfield et al., 1984). De Castro (1985) showed that families with at least one sick member tended to shift the workload to healthy family members, thereby reducing (and also spreading) the net economic costs of the disease.

Despite the work of these and other researchers, the precise effect of malaria on productivity is still an open question. Using direct measure-

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