Figure 2. Sketch diagram of conversion principle from simulated outbreak data to syndromic data.

Clinic visits data were used as an example; a_i is the probability of patients visiting doctors at day i; n_i is the number of new outbreak cases at day i. The number of new cases at day 1 is n₁. Of these, a₁n₁ cases will visit doctors in clinics on that day; a₂n₁ cases will visit doctors on the second day; a₃n₁ will do so on the third day (light blue pillars), etc. On day 2, there are n₂ new cases, of which a₁n₂ cases will visit doctors in clinics on that day; a₂n₂ cases will do so on the second day; a₃n₂ will do so on the third day (green pillars), etc. As a result, the sum of the visiting volumes on day 1 is a₁n₁; on day 2, it is a₂n₁ + a₁n₂; on day 3, it is a₃n₁ + a₂n₂ + a₁n₃; etc.