[vanusa]

If we think in terms of a race -- an IQ of 100 puts you at the 50th percentile -- so half of the contestants are faster than you, and the other half are slower.

A loss of 6-8 points puts you at about at about the 35th percentile -- meaning 65 percent of the people in the race will be running more faster than you. Or (back in real life terms) be that much more likely to get admitted to college, get a decent job / spouse, and so on.

That is, to the extent that definitions of IQ are valid and can be measured accurately, and so on. But given the amount of research that has gone into this -- and we know a lot more now that we did a few decades ago -- it seems the risks (of heavy cannabis use) are potentially quite serious.

(BTW, as to how one gets from "6-8 points" to "35th or 40th percentile": it has to do with how the IQ scale is defined. By the traditional scale approximately two-thirds of the population scores are between IQ 85 and IQ 115. Meaning (on a scale from 1 to 100) 15 points of IQ equals a difference of about 33 percent. So 6-8 points is about half that, or very roughly 15 percent).