DF = data.frame(
    treatment=c( rep( 'A', 4 ), rep( 'B', 4 ), rep( 'C', 4 ), rep( 'D', 4) ),
    value=c( 16, 17, 16, 17,
              4, 12,  2, 26,
             26, 22, 23, 24,
              8, 9,  11, 8 )
)