I agree with NJ "I find it difficult to understand how racial bias can influence sentencing, particularly concerning imprisonment from Magistrates’ courts. Magistrates’ sentencing guidelines are quite rigid..."
And the same applies to the decision to whether to caution an accused:
"It shows that over the past four years black criminals have been less likely to receive police cautions and more likely to have been proceeded against in court, than any other ethnic groups."
When the police seek advice from the CPS or a decision maker on how to proceed with a case a persons colour does not even come into the process, (unless it has some bearing on the case e,g racially motivated offences). the prosecutor doesn't say "what colour is the accused" nor would an officer say "just to let you know the accused is black"
This will be a difficult study to establish any accuracy as rarely are two offences exactly the same.