I can't read the article because of the paywall. But I have to say, when I was single several years ago, my happiness was maybe a 4-5 on a scale of 1-10. I used to feel lonely all the time. Right now I'm married and expecting our first child, and I'd rate it a 7-8 (depending on my mood). Some of that is from being more financially secure though.
I'd guess that in general, some financial security comes from a stable relationship: a shared living environment, efficiencies of scale with things like shopping/cooking, car ownership potentially, utilities from heating/cooling, common cause on other fronts.
Having kids have brought me more happiness and more pain than anything else I have ever done. Using you scale, if I was 5-7 when single and 6-8 when married with no kids, having kids changed it to 2-10.
