\begin{Schunk}
\begin{Sinput}
 head(datX)
\end{Sinput}
\begin{Soutput}
   ID Year Quarter       pop illnesses
1 USA 1990      Q1 10.583188 106.91171
2 USA 1990      Q2  8.693201 108.23795
3 USA 1991      Q1  9.459614 121.45065
4 USA 1991      Q2 11.947693  76.53056
5  UK 1990      Q1 10.053590 101.49592
6  UK 1990      Q2 10.351663  86.57469
\end{Soutput}
\begin{Sinput}
 head(datY)
\end{Sinput}
\begin{Soutput}
  Country year Semester percipitation      cars
1     USA 1990       Q1      9.413120  89.50647
2     USA 1990       Q2      8.167623 123.30512
3     USA 1991       Q1     10.888139 114.02705
4     USA 1991       Q2     11.593488 109.42601
5      UK 1990       Q1     10.516855 108.26258
6      UK 1990       Q2      8.704328  91.88460
\end{Soutput}
\end{Schunk}
