Or correlation with basically everything else. I sleep better when in a separate room than my wife, because if that happens that's probably because she was being nice and shielded me from my morning duties, and let the kid jump in her bed in the morning.
In order for those measure to make any sense OP would need to follow the exact same routine with and without his girlfriend (in the same flat of course). Otherwise it is measuring the general effect of living with somebody (different activities, different morning arrangement, different commute, ...) rather than the specific sleeping arrangement effect.
Now I'm not discarding the effect, however after a few years together, you start getting used to your bed partner. The stuff that really matters is if you have enough room and sheets to make it work. In the extreme case, a queen size bed is basically 2 single bed joined together and is a cheaper alternative than the extra half a million an extra bedroom costs.
edit: reread the article and it seems OP actually talk more about the effect of living with somebody rather than the physical sleeping arrangement. Comments were drifting in the "physical" direction at the time I commented.
I definitively share the same experience - obviously with a kid and wife, I have much less freedom in my night and morning routine. Not sure I'm sleeping better, my wife definitively is - her stress level is way lower when she knows I'm home and she sleeps more deeply, not woken up by every little noise (the effect has been mitigated slightly since we have a child though)
In order for those measure to make any sense OP would need to follow the exact same routine with and without his girlfriend (in the same flat of course). Otherwise it is measuring the general effect of living with somebody (different activities, different morning arrangement, different commute, ...) rather than the specific sleeping arrangement effect.
Now I'm not discarding the effect, however after a few years together, you start getting used to your bed partner. The stuff that really matters is if you have enough room and sheets to make it work. In the extreme case, a queen size bed is basically 2 single bed joined together and is a cheaper alternative than the extra half a million an extra bedroom costs.
edit: reread the article and it seems OP actually talk more about the effect of living with somebody rather than the physical sleeping arrangement. Comments were drifting in the "physical" direction at the time I commented. I definitively share the same experience - obviously with a kid and wife, I have much less freedom in my night and morning routine. Not sure I'm sleeping better, my wife definitively is - her stress level is way lower when she knows I'm home and she sleeps more deeply, not woken up by every little noise (the effect has been mitigated slightly since we have a child though)