INTERVAL CENSORED SURVIVAL-DATA AND MULTISTATE COMPARTMENTAL-MODELS IN THE ANALYSIS OF FIRST APPEARANCE OF PLASMODIUM-FALCIPARUM PARASITES IN INFANTS

A statistical model for interval censored data is described. Assuming a piecewise constant incidence enables us to analyse very unbalanced d ata in a generalized linear model. The distribution of age at first ap pearance of P. falciparum parasites in infants in Liberia has been est imated. A new graphical method for presentation of test results on all children was developed. In an illness - death model it is described h ow the proportion of undetected and detected malaria parasitemias depe nds on parasite rates and testing frequency. The incidence of detectab le malaria parasitemia was 0.14 per month in infants under 4 months of age, and 0.60 per month in children over 4 months (p < 0001). The con genital resistance to malaria in African infants living in a highly en demic area had largely disappeared by the age of 4 months; before this age children were partly protected.