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Table 1 The comparisons of time series components between the series of mild and severe HFMD cases

From: Comparisons between mild and severe cases of hand, foot and mouth disease in temporal trends: a comparative time series study from mainland China

Components Mild HFMD cases Severe HFMD cases ratio/differencea p-value*
Long-term linear trend
 Biennial increase (%) 124.46 (122.80, 126.14) 91.20 (89.69, 92.74) 1.36 (1.34,1.39) <0.001
Semi-annual cycle
 peak value 1.04 (1.00,1.07) 0.87 (0.82,0.93) 1.19 (1.11,1.27) <0.001
 peak time (days) 134.7 (133.77,135.68) 131.48 (129.83,133.13) 3.21 (1.42,5.08) <0.001
Eight-monthly cycle
 peak value 0.24 (0.20,0.27) 0.21 (0.16,0.26) 1.14 (0.88,1.52) 0.081
 peak time (days) 97.47 (91.34,103.51) 74.78 (64.86,83.81) 22.69 (11.03,34.24) 0.001
Annual cycle
 peak value 1.78 (1.73,1.83) 3.08 (2.97,3.19) 0.58 (0.55,0.60) <0.001
 peak time (days) 183.08 (181.79,184,48) 176.52 (175.27,177.77) 6.56 (4.89,8.52) <0.001
Biennial cycle
 peak value 0.40 (0.36,0.43) 0.80 (0.75,0.86) 0.49 (0.44,0.56) <0.001
 peak time (days) 466.49 (456.14,477.35) 492.55 (483.99,502.11) −26.06 (−40.96,−11.92) <0.001
First year cycle of the overall periodic curve
 Start time (days) 36 (35,38) 27 (25,29) 9 (7,11) <0.001
 Major peak time (days) 155 (153,156) 156 (155,158) −1 (−3,0) 0.012
 Major peak value 1.23 (1.19,1.28) 2.10 (2.00,2.19) 0.59 (0.56,0.62) <0.001
 Minor peak time (days) 288 (284,292) - - -
 Minor peak value 0.44 (0.42,0.47) - - -
Second year cycle of the overall periodic curve
 Start time (days) 391 (390,392) 377 (375,379) 14 (11,16) <0.001
 Major peak time (days) 510 (509,511) 513 (512,514) −3 (−4,−1) <0.001
 Major peak value 1.90 (1.85,1.96) 4.20 (4.07,4.34) 0.45 (0.43,0.47) <0.001
 Minor peak time (days) 661 (659,664) - - -
 Minor peak value 0.42 (0.36,0.44) - - -
  1. The 95 % confidence interval of model estimates were given in the following bracket
  2. ato compare two series, we calculated the relative difference (i.e. the ratio of mild case to severe case) for the biennial increase and the peak value of cycles, whereas the absolute difference (i.e. mild case minus severe cases) was calculated for the start and peak timing. We applied a quasi-Poisson model to estimate the time series components in which a log function is used to link the observed values and linear predictor. Therefore, the ratio of biennial increase and peak value between two series is equivalent to the absolute difference between their related linear predictors. However, the start and peak timing will not be affected by the log link function
  3. *The p-value was calculated to test the equality of time series components between two series, with the null hypothesis of no difference (i.e. the ratio equals 1 or difference equals to 0)