Today is National Grammar Day, a reminder that good grammar is instrumental in conveying ideas with clarity, professionalism, and precision. Even so, the informality of e-mail, texting, and tweeting has crept deep into company communications. It is not uncommon to hear a coworker make a grammatical faux pas such as “There’s new people you should meet.” Even former Yahoo! CEO Jerry Yang was known for ignoring capital letters in his e-mails.

Kyle Wiens, CEO of iFixit, wrote in a blog post for HBR that he refuses to hire people who use poor grammar. He asserted that good grammar is a sign of professional credibility, attention to detail, and learning ability. In the process, he started a nearly 4,000-comment debate (on this website alone) about the audaciousness of his stance. Some people criticized Mr. Wiens for his hiring approach, accusing him of being harsh or even elitist. Ultimately, this was a debate that had no data and reached no conclusion.

In an effort to add evidence to the commenters’ anecdotes, my company, Grammarly, reviewed 100 LinkedIn profiles of native English-speakers in the consumer packaged goods industry. Each professional had worked for no more than three employers over the first 10 years of his or her career. Half were promoted to director level or above within those 10 years, and the other half were not.

Here’s what we found:

Professionals with fewer grammar errors in their profiles achieved higher positions. Those who failed to progress to a director-level position within the first 10 years of their careers made 2.5 times as many grammar mistakes as their director-level colleagues.

Fewer grammar errors correlate with more promotions. Professionals with one to four promotions over their 10-year careers made 45% more grammar errors than those with six to nine promotions in the same time frame.

Fewer grammar errors associate with frequent job changes. Those who remained at the same company for more than 10 years made 20% more grammar mistakes than those who held six jobs in the same period. This could be explained in a couple of ways: People with better grammar may be more ambitious in their search for promising career opportunities, or job-hoppers may simply recheck their résumés between jobs.

Granted, this is a relatively small sample size. We do not know whether the relationship is causal or if good grammar merely correlates with career success. It is also possible that professionals who were promoted to director level started their careers with poor grammar skills. If so, they significantly improved their skills over the past 10 years, and it is unlikely that all their progress occurred after they became directors. Perhaps follow-up studies can fill these holes in the analysis.

What we can say is that this data set clearly supports the hypothesis that good grammar is a predictor of professional success. The results are not surprising. As Wiens would argue, grammar skills may indicate several valuable traits, such as:

Attention to detail: People who care about their writing demonstrate credibility, professionalism, and accuracy in their work.

People who care about their writing demonstrate credibility, professionalism, and accuracy in their work. Critical thinking: Knowing how to structure a grammatically correct sentence is a sign that you can analyze and explain complex problems.

Knowing how to structure a grammatically correct sentence is a sign that you can analyze and explain complex problems. Intellectual aptitude: If you are a native English-speaker and never learned the difference between “it’s” and “its,” especially given access to Google, an employer might wonder: What else have you failed to learn that might be useful?

Interestingly, there were virtually no spelling mistakes in the 100 LinkedIn profiles we analyzed. This is probably because of the prevalence of spell check, which performs a relatively simple computer recall task. By contrast, grammar analysis is very complex, requiring a deep understanding of the relationships between words. For this reason, grammar provides a better window into a job applicant’s abilities.

Companies looking to hire top talent should consider grammar as one predictor of a candidate’s aptitude and success. Good grammar is simply good business.