The following chart shows the cumulative score by round for each of the last three tournaments. If the details are too small to read, you can find the same tables on three pages:-
The winners of each event are circled in red (in 2013 Carlsen beat Kramnik on tiebreak), as are the players with a plus score after round 3. I've also indicated the leaders after round 7, the halfway point of the tournament, when the participants have played each other once.
In all three tournaments, the eventual winner was from the group of players who had a plus score after round 3. The winner was also one of the leaders after the first half of the tournament. The following table shows the leaders after round 3 in the 2018 Berlin Candidates.
2.0 Caruana, Mamedyarov
1.5 Ding Liren, Grischuk
1.0 Aronian, Karjakin
0.5 Wesley So
If past is prologue (it's usually not!), then the eventual winner will be one of Kramnik, Caruana, or Mamedyarov. It's curious to note that in each of the last three events, GM Aronian was one of the leaders at mid-point, then faltered in the second half. It's also curious that the ultimate winning score was always 8.5-5.5, or plus-three as they say in the lingo.