It has been well established in literature that the likelihood of apprehension is an important factor. I think that is borne out both in experience and in the data.
On the other hand, the notion that the penalty itself will be a deterrent is borne out neither by the literature, in my view, nor by my experience. I have been working in prisons for 38 years and I can't remember ever a circumstance where a person said that, given that the mandatory minimum was four years, he thought it was worth it, but now that it's going to be five years, there's no way he's going to consider that offence.
I haven't known anyone who knew what the mandatory was and I have had no one who ever gave any indication that it was part of his thinking. So I find the literature in fact confirms the actual experience that I've seen in the prisons.