As 2017 Ashes series is decided, a general question is posed. This query is applicable to all format, and between any teams playing at all level.
Q -When you have already won or loss the series convincingly, do you drop out-of-form batsman for last test of series ?
1- You still pick him and ask him to play with no pressure. As a captain you could easily observe his maturity. If he fails to score runs, and captain feels he is not adapted to failure then he can be dropped for next series. Here one needs to be transparent to what role play he will have with the team in near future.
2- If you drop him and pick a debutant or someone who already played test cricket –
a) If he fails too, then you have to drop him also, meaning 2 players have been dropped in successive test matches. Not having consistent selection policy.
b) If he performs well -it would be hard to find his responsibility under pressure.
In Australia’s case there is constant change in playing XI (either through injury or poor form). Since June 2015 they had 10 test debutants (Adam Voges, Peter Nevill, Jon Holland, Callum Ferguson, Joe Mennie, Peter Handscomb, Nic Maddinson, Matt Renshaw, Hilton Cartwright and Cam Bancroft).
Since the time I am updating Australia cricket stats (Nov 1998) they had 73 debutants in 226 Test matches. Below is brief list of which test match debutants are more frequent
1st Test – 34
2nd test – 16
3rd Test – 14
4th Test – 6
5th Test – 2
Here is a link to selection policy – http://allthatcricket.com/?p=8940