When it comes to relationships, it’s not what you say but how you say it that makes all the difference.

At least that’s what a new study from the University of Southern California suggests.

Researchers used a computer algorithm program to analyse the tone of speech couples used to determine whether they would stay together in the long run and found it is incredibly revealing.

A team led by Shrikanth Narayanan and Panayiotis Georgiou from the university's School of Engineering used the new algorithm they developed to record hundreds of conversations between over 100 couples during their marriage therapy sessions over the course of two years.

They then followed each relationship for a following five years.

And by assessing the tone of voice used in the therapy sessions – such as pitch, intensity and ‘jitters' that track aspects of emotion in the voice – the algorithm was able to predict if the relationship between spouses would improve or deteriorate across the period.

It was accurate 79% of the time.

In fact, it was more accurate at predicting the outcome of the marriage than experienced relationship experts, who analysed behavioural aspects of the relationship such as blame and acceptance.

The one subtle part of speech that helps predict whether your relationship will last