Something to consider when making selections.

TOP Jockeys that have ridden the horse before.

Been going through recent results and will have some figures soon. Usually if a TOP Jockey has ridden the horse before, they stick with a horse with the potential to win.
Not saying it works every time but it seems to have a much better strike rate.

Any thoughts?

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Treat your selection and staking methods not with optimism, nor with pessimism, but with realism.

What if there are 6 horses in the same race which have retained the same jockey from its last race??

I think its a bit like last start winners.

The stat needs to be combined with several others to be of use.

Maybe the jockey can't get a better ride for instance -so is stuck with this horse?

Where this would be helpful is to follow the horse/jockey combo over a few starts, not necessarily to pick the winner of a certain race. There are exceptions...as you noted chief.
But I have seen the TOP jockeys usually stay with TOP horses...unless sacked or other stable commitments.