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Characteristics of investigations in Zhejiang Province in 1998 and 2006
| Survey date | Sample resource | Sample size(n) | Male/ female | Detection method | Serum retinol(μmol/L) | No. Of VAD(%) |
| October 1998 | 13 counties | 1842 | 968/874 | fluorescence | 1.62 ± 0.92 | 145(7.8) |
| April2006 | 6 counties | 357 | 188/169 | HPLC-UV | 1.65 ± 0.47 | 11(3.08) |
Incidence of VAD, χ2 = 10.41, P = 0.001
