The data include these as additions to savings. They do not include capital gains, so on this account, as I take you to imply, the rate is understated (e.g., fixed amount missing from numerator and denominator).
This is consistent with your remark about behavior. On the other hand, a lot of this extra income is being spent, rather than saved, which goes the other way.
> . . .
>It would be interesting to see some kind of research into the savings rate
of those who don't have access to a defined
>contribution plan (last I checked, it was less than half of
>the full-time workforce)
Very low, is my understanding.
MBS