Stanford University: The real strength of weak ties

A team of researchers from Stanford, MIT, Harvard, and LinkedIn recently conducted the largest experimental study to date on the impact of digital job sites on the labor market and found that weaker social connections have a greater beneficial effect on job mobility than stronger ties.

“A practical implication of the research is that it’s helpful to reach out to people beyond your immediate friends and colleagues when looking for a new job,” explained Erik Brynjolfsson, who is the Jerry Yang and Akiko Yamazaki Professor at Stanford University. “People with whom you have weaker ties are more likely to have information or connections that are useful and relevant.”

Brynjolfsson co-led the first large-scale, longitudinal, experimental study on the “strength of weak ties,” one of the most influential social theories of the last 100 years. The “strength of weak ties” theory maintains that infrequent, arms-length relationships – known as weak ties – are more beneficial for employment opportunities, promotions, and wages than strong ties.

“Despite having over 65,000 citations in the last 50 years, there have been no large-scale experimental causal tests of this theory as it relates to employment,” explained Sinan Aral, a professor at the MIT Sloan School of Management who co-led the study.

The team’s findings are detailed in a paper, titled A causal test of the strength of weak ties that published this week in the journal Science.

The strength of weak ties theory is based on the idea that weak ties allow distant clusters of people to access novel information that can lead to new opportunities, innovation, and increased productivity. The author of this theory, Mark Granovetter, argued in 1973 that weak ties are particularly helpful in delivering new employment opportunities because they introduce novel labor market information to a broader social network.

Yet, the largest empirical tests of this theory to date had discovered what scientists called “a paradox of weak ties,” in which strong ties, not weak ones, were the ones that seemed to be delivering jobs. Unfortunately, since these previous studies were not experimental, they could not reliably pin down the causal effects of weak and strong ties on labor mobility.

In their study, the research team overcame these hurdles by conducting a five-year set of experiments on LinkedIn with 20 million people around the world, during which 600,000 new jobs were created. They used data from large-scale randomized experiments conducted on LinkedIn’s “People You May Know” (PYMK) algorithm to test the weak tie theory and its impact on the labor market.

“LinkedIn was a great platform for us for three reasons,” explained Brynjolfsson. “First, the theory we are testing is about the effect of ties on finding jobs and LinkedIn is a leading platform for job seekers. Second, LinkedIn did a series of experiments so we could really understand the causal effects of tie strength. Third, the size of the platform allowed us to do this all at an economically and statistically significant scale.”

By randomly assigning some LinkedIn users to receive more weak tie recommendations from the PYMK algorithm and other users to receive more strong tie recommendations, and then examining the labor mobility of the two groups over five years, their analysis confirmed that weaker ties increased the likelihood of job mobility the most. But the researchers also found an inverted U-shaped relationship between tie strength and job mobility, with moderately weak ties increasing job mobility the most and the strongest ties increasing job mobility the least.

“It’s not a matter of ‘the weaker the better’ or ‘the stronger the worse,’ ” explained study co-leader and Harvard Business School Professor Iavor Bojinov. “Our results show that the greatest job mobility comes from moderately weak ties – social connections between the very weakest ties and ties of average relationship strength.”

Further, the researchers looked at differences across industries and found that adding weak ties creates significantly more labor market mobility in digital and high-tech sectors of the economy. Weak ties led to more job applications than strong ties in industries with greater IT intensity, software intensity, robotization, and industries more suitable for machine learning, artificial intelligence, and remote work.

“We found that weak ties create significantly more labor market mobility in digital and high-tech sectors. This may reflect the fact that there is more rapid change and need for novel information and connections in those industries,” Brynjolfsson said.

He points out that the traditional methods used by policymakers to analyze labor markets are incomplete and quickly becoming outdated. “Policymakers need to recognize that the labor market, like all aspects of the economy, is being digitized,” Brynjolfsson said. “It is incredibly important that we understand how the algorithms used by digital platforms like LinkedIn impact the labor market, employment rates, and the broader health of the global economy. These digital platforms and the algorithms that run them have become essential labor market drivers.”