Don’t see the value of a mobile-friendly website? A new study by Google might change your mind.

According to “What Users Want Most From Mobile Sites Today,” 61 percent of Internet users will leave a site if it is not mobile-friendly. The study, which surveyed 1,088 U.S. smartphone users, also revealed that 48 percent of users become frustrated and annoyed when they reach a site that is not mobile-friendly.

These numbers are hard evidence of the continuing shift toward mobile web surfing—including on association websites—and they are not going away.

For associations considering the advantages of a mobile-friendly site, “you have to start with the numbers,” said Layla Masri, president of Bean Creative, a studio of interactive design and development experts. “It’s not about whether the board thinks that a lot of people might be on a tablet or phone. It’s that people really are. Now more than ever it’s really important to make sure that you’re optimized for mobile devices.”

Mobile-friendly websites are an important factor in membership growth, too.

“A little over two-thirds of Americans in the 24- to 35-year-old age range have a smartphone,” Masri said. “The people that are going to be coming into the ranks of membership associations are going to expect to be able to do many, if not all, of the things they would do on a desktop website on a mobile device.”

Keeping up with the Joneses in terms of mobile-friendly development can also prove important for an organization’s brand. Fifty-two percent of those surveyed in the Google study said they are less likely to engage with a company after a bad mobile experience.

“If people are going to your site and finding that it’s doesn’t render well, or it renders so poorly that it’s almost useless for them, then they have a perception of your brand that you’re not keeping up with the times, that you’re not understanding where they are and what they need,” Masri said, “and that reflects poorly upon your brand.”