First there is what criminologists call the "dark figure". It is a bit like the way in which 19th century explorers referred to the Dark Continent of Africa. We know its there, we have an idea of what it looks like, we may even have an idea how big it is, but to a large extent it is uncharted territory. The dark figure, in its most undefined sense, is the difference between the crime that occurs and that which features in official crime statistics.
Now we then get into the sticky problem of what is a crime anyway. We will park that to one side for the moment because I could write numerous quite technical blog entries on that subject alone.
In England and Wales a crime in its most narrow sense is an offense that Home Office police forces are required to tell the Home Office about so the Home Office can compile their official statistics. These are known as notifiable offences. These are mainly offences that involve theft, violence or of a sexual nature or drug related. Importantly, antisocial type behaviour such as drunkenness, begging and littering though against criminal law are not notifiable offences. Equally road traffic offences, except the most serious, are not either.
Next we come to Home Office counting rules. These are no doubt very logical but fiendishly boring. Suffice to say that even if a notifiable offence has occurred the times it is counted as having occurred varies with the circumstances in which comes to police notice. For instance, from memory, and it might have changed (one of the problems of comparing year to year official recorded crime), if a series of the same crime has occurred in the past with the same victim and it is the first time it has come to police notice then that is counted as one crime. But future crimes, if reported to police individually, are counted separately.
So we have now got an idea of a narrow set of crimes, but to be fair include all the serious crimes, and a rigid set of counting rules. The dark figure in its most defined sense are those crimes that would have featured in the official statistics but do not because the police did not discover them or more commonly were not reported to them by the victim or other person.
Ok, so that's the dark figure.