I have seen a lot of posts recently on some anti poly websites which basically consider Polyamory as nothing more than swinging by another name, this was a post I wrote previously on this topic.
I see a HUGE difference between an emotionally and materialistically monogamous couple getting together with other couples for sexual purposes
a couple opening up their relationship to one or more people to share their lives sexually, emotionally and materially.
Swinging by its nature is about change and variety, it is supposed to enhance the marriage of the couple by giving them an alternative sex life but keeping their home life entirely separate.
I have only known one couple who tried swinging and they did break up, swinging wasn't the reason though, the reason was she was sick of the marriage and wanted out, desperation makes people consider things they might not normally consider just to make their marriage exciting again. So it was more the symptom than the cause.
I do know a few single people who have had connections to the swinging world and from what I recall, what you would get is a great many of the wives in the kitchen chatting together whilst their husbands were upstairs, The consensus was that they had no interest in it themselves but their husbands would just have an affair if they didn't and they would rather see what they were getting up to.
I don't know 100% because I have not been involved personally with swinging but from what I recall from the various conversations, is that swinging seems more male led and dominated and Poly seems more female led and dominated (though that might upset the Patriarchal folks, the stats don't lie). When women want something to work it works, when they don't, it won't work.
So like everything, it depends greatly on the people (especially women) involved.
If Poly (or swinging or anything that dramatically changes the nature of a particular marriage) is used as a sticky plaster/band aid for a marriage already failing I would say work on your marriage first. If either partner is falling out of love with the other one then Poly will not help. If it isn't something that both people want and/or something they have always intended for their lives (openly, I hasten to add - saying, I always wanted to be polyamorous and so five/twenty-five years into my monogamous marriage with Jackie, I admitted it to her, does not count!) than it probably would be doomed to failure.
If the Primary feels like s/he is being pushed into it, it will fail, if the secondary partner is only going into it because s/he likes the husband/wife (but not poly) or s/he thinks it is something cool and fashionable because it is on HBO, it will fail.
I have never heard about a scientific survey about poly but it would be of great interest to me to be involved in a research study (my scientific brain is going just thinking about it) but you do run the risk of it not being taken seriously by the scientific establishment, after all, what do you consider a successful and healthy poly group? Those who have been together 5, 10, 15, 20 years plus? Is there a standard time line for 'successful'? What if you interview 200 poly families, who you consider successful and ten years down the line they have all divorced? As a scientist, the better option would be to follow a number of couples over a number of years monitoring them every year to check how happy, stable and functional the family are.
You also run the risk of poly people themselves not caring for any conclusion you draw, for example, if you admit ALL poly situations you will likely have those saying 'We are not like that because we are FLDS/Christian/Patriarchal/Egalitarian/polyamorous/bisexual/open/closed/whatever.
In other words there are so many variables that you can either choose to involve everything (which would mean that some will disregard how meaningful it is) or narrow it down, in which case it won't actually show the full scope of polyamorous groupings and therefore it will be scientifically useless.