Observations over three waves. For each population there was information on N individuals, of whom N1 reported symptoms in wave 1 and N0 did not; in wave 2, N12 had a repeat attack, while N10 of those affected in wave one did not have a repeat attack; N123 individuals reported symptoms in all three waves...;;etc. The total number reporting symptoms in wave 2 was N12 + N02, while the total number for wave three was N123 + N103 + N023 + N003. The observed numbers N123, N120, N103, N100, N023, N020, N003, N000 for each population can be recovered from the proportions SAW, SA-, S-W, S- -, -AW, -A-, - -W, - - - shown in Table 1 by multiplication by the corresponding N.
Mathews et al. BMC Infectious Diseases 2010 10:128 doi:10.1186/1471-2334-10-128