One unit equals 8g of pure alcohol. A drink is:What's a unit here?
12oz Beer (how strong is beer?)
5oz Wine (1.7 units @ 14%)
1.5oz Spirits (2 units @ 40%)
4 drinks / day = 52 units / week
½ drink / day = 6.5 units / week
I think the effect that is being measured here is mostly what El Mac says.