Closeness between couples is reflected in the distance separating them as they sleep, a study has found.
Partners who slept less than 2.5cm apart were more likely to be happy with their relationship than those maintaining a gap wider than 76cm.
In addition, more couples who spent the night making physical contact were happy than those with a "no touching" rule while trying to sleep.
The survey of 1000 people, conducted as part of the Edinburgh International Science Festival, also revealed the most popular sleep positions of couples, with 42 per cent lying back to back, 31 per cent facing the same direction and four per cent facing one another.
Twelve per cent of couples spent the night less than 2.5cm apart, while just 2 per cent were separated by more than 76cm.
University of Hertfordshire psychologist Professor Richard Wiseman, who led the study, says: "One of the most important differences involved touching. Ninety-four per cent of couples who spent the night in contact with one another were happy with their relationship, compared to just 68 per cent of those that didn't touch.
"This is the first survey to examine couples' sleeping positions, and the results allow people to gain an insight into someone's personality and relationship by simply asking them about their favourite sleeping position."
The study found that 86 per cent of couples who slept less than 2.5cm away from each other claimed to be happy with their relationship, compared with 66 per cent who slept more than 76cm apart.
Extroverts tended to spent the night close to their partners, and more creative individuals were more likely to sleep on their left-hand side.
Prof Wiseman is the author of Night School, which examines the science of sleep and dreaming.