What has been called "attachment parenting"* has become ever so trendy in recent years and for a lot of parents of very young infants there is a whole set of things that goes together under this heading. This tends to include breastfeeding on demand, sleeping in a family bed, carrying in a sling for a lot of the day, and responding very quickly when infants cry - never leaving them to cry when nothing obvious is wrong. Another group of parents - again hugely stereotyping here - go more for scheduled feeding, own bed, and putting in a baby seat or buggy rather than carrying the baby in a sling.
It's pretty hard to randomise parents to different groups and tell one "right, you lot sleep with baby in the bed but use a pushchair and feed on a schedule, and you lot over there, let's have feeding on demand but even if you think it's part of the package, don't have them in the bed with you or carry them in a sling".
However, infants in most cultures cry a lot and parents complain of them crying a lot, especially in the first three months. So it's probably safe to say that parents in two different European countries are both going to be complaining of infants crying and if they it might be helpful to compare how much the babies cry if infant care practices are different.
In fact, it turns out they are - the two stereotyped groups I've described above are both groups found commonly in the UK but in Denmark, practices are a little different - even parents who don't sleep in a family bed or feed on demand, tend to hold or carry the baby for longer each day. So it's possible to separate the effect of sleeping in a family bed and feeding on demand (the "attachment parenting" or "non-conformist", mainly UK group) from the effect of a high level of responsiveness and carrying (the Danish group).
What the study found was that it was the carrying and responsiveness - as practiced by "mainstream" Danish mothers - that led to less crying during the day and evening (and it's the evening crying that parents find so wearing). Sleeping together in one bed in particular didn't help crying or sleeping through the night. In fact, sleeping in one bed added on to carrying/holding made infants less likely to have a settled, all-night sleep with little crying by 3 months.
What was also interesting was that extreme crying - "colic", which really seems to have little to do with the digestive system - was no different between the groups. So "regular" cryers cry less in the daytime if they are held more, more at night if they are in a family bed, but "extreme" cryers are not a result of anything parents have or have not done. Frustrating if you have one of them, but a little bit reassuring if you are worried you are doing something wrong.
*It's a very distinct style of parenting which some parents prefer but there's no evidence it has much to do with attachment - I'm going to be writing on that shortly** so bear with me.
**i.e. some time this millennium
If you are interested:
Pediatrics. 2006 Jun;117(6):e1146-55. Infant crying and sleeping in London, Copenhagen and when parents adopt a "proximal" form of care. St James-Roberts I, Alvarez M, Csipke E, Abramsky T, Goodwin J, Sorgenfrei E.