A data frame with the 168 monthly observations (from January 1970 to December 1983) with the following variables
y | time series of polio incidences. |
t*10^( -3 ) | linear trend multiplied by factor \(10^{(-3)}\). |
cos( 2*pi*t/12 ) | cosine annual seasonal component. |
sin( 2*pi*t/12 ) | sine annual seasonal component. |
cos( 2*pi*t/6 ) | cosine semi-annual seasonal component. |
sin( 2*pi*t/6 ) | sine semi-annual seasonal component. |