If you look at IMF predictions of world GDP [1] you can see that simply taking last year's value would have had lower error for most years and in average. [1]

If you look at IMF predictions of world GDP [1] you can see that simply taking last year's value would have had lower error for most years and in average. [1] -- figure 2 https://www.ft.com/content/60581224-3335-11e8-b5bf-23cb17fd1498 https://www.ft.com/content/60581224-3335-11e8-b5bf-23cb17fd1...