Use it or lose it artifact creates 12-month seasonality
suppressPackageStartupMessages({
library(fpp2)
})
# Monthly government expenditure (millions of dollars) as part of the Pharmaceutical Benefit Scheme for products falling under ATC code A10 as recorded by the Australian Health Insurance Commission. July 1991 - June 2008
a10
#> Jan Feb Mar Apr May Jun Jul
#> 1991 3.526591
#> 1992 5.088335 2.814520 2.985811 3.204780 3.127578 3.270523 3.737851
#> 1993 6.192068 3.450857 3.772307 3.734303 3.905399 4.049687 4.315566
#> 1994 6.731473 3.841278 4.394076 4.075341 4.540645 4.645615 4.752607
#> 1995 6.749484 4.216067 4.949349 4.823045 5.194754 5.170787 5.256742
#> 1996 8.329452 5.069796 5.262557 5.597126 6.110296 5.689161 6.486849
#> 1997 8.524471 5.277918 5.714303 6.214529 6.411929 6.667716 7.050831
#> 1998 8.798513 5.918261 6.534493 6.675736 7.064201 7.383381 7.813496
#> 1999 10.391416 6.421535 8.062619 7.297739 7.936916 8.165323 8.717420
#> 2000 12.511462 7.457199 8.591191 8.474000 9.386803 9.560399 10.834295
#> 2001 14.497581 8.049275 10.312891 9.753358 10.850382 9.961719 11.443601
#> 2002 16.300269 9.053485 10.002449 10.788750 12.106705 10.954101 12.844566
#> 2003 16.828350 9.800215 10.816994 10.654223 12.512323 12.161210 12.998046
#> 2004 18.003768 11.938030 12.997900 12.882645 13.943447 13.989472 15.339097
#> 2005 20.778723 12.154552 13.402392 14.459239 14.795102 15.705248 15.829550
#> 2006 23.486694 12.536987 15.467018 14.233539 17.783058 16.291602 16.980282
#> 2007 28.038383 16.763869 19.792754 16.427305 21.000742 20.681002 21.834890
#> 2008 29.665356 21.654285 18.264945 23.107677 22.912510 19.431740
#> Aug Sep Oct Nov Dec
#> 1991 3.180891 3.252221 3.611003 3.565869 4.306371
#> 1992 3.558776 3.777202 3.924490 4.386531 5.810549
#> 1993 4.562185 4.608662 4.667851 5.093841 7.179962
#> 1994 5.350605 5.204455 5.301651 5.773742 6.204593
#> 1995 5.855277 5.490729 6.115293 6.088473 7.416598
#> 1996 6.300569 6.467476 6.828629 6.649078 8.606937
#> 1997 6.704919 7.250988 7.819733 7.398101 10.096233
#> 1998 7.431892 8.275117 8.260441 8.596156 10.558939
#> 1999 9.070964 9.177113 9.251887 9.933136 11.532974
#> 2000 10.643751 9.908162 11.710041 11.340151 12.079132
#> 2001 11.659239 10.647060 12.652134 13.674466 12.965735
#> 2002 12.196500 12.854748 13.542004 13.287640 15.134918
#> 2003 12.517276 13.268658 14.733622 13.669382 16.503966
#> 2004 15.370764 16.142005 16.685754 17.636728 18.869325
#> 2005 17.554701 18.100864 17.496668 19.347265 20.031291
#> 2006 18.612189 16.623343 21.430241 23.575517 23.334206
#> 2007 23.930204 22.930357 23.263340 25.250030 25.806090
#> 2008
autoplot(a10) + theme_minimal()

ggseasonplot(a10) + theme_minimal()

ggsubseriesplot(a10) + theme_minimal()

cbind("Sales ($million)" = a10,
"Monthly log sales" = log(a10),
"Annual change in log sales" = diff(log(a10),12)) %>%
autoplot(facets=TRUE) +
xlab("Year") + ylab("") +
ggtitle("Antidiabetic drug sales") + theme_minimal()

nsdiffs(a10)
#> [1] 1