Alt text is vital in digital marketing. It makes visual content accessible for individuals who use an assistive device or program to access and navigate through digital spaces. Alt text also notably impacts Search Engine Optimization (SEO) when applied to images on websites, making it more likely that online users find and engage with your content.
However, there is little to no concrete data to support whether or not alt text impacts the engagement of images on social media platforms like Facebook, Twitter/X, Instagram, and LinkedIn.
Content creators have experimented with keywords and the alt text field on Instagram with varied results. Most have noticed that keywords in the alt text field can affect the searchability of a post within the app. A decision was made to conduct a year-long A/B test that analyzed how alt text possibly impacted the engagement of posts on Twitter, if at all.
Every day at 10:00 a.m. ET, two tweets would post from Sprout Social. They were seemingly identical with the exception of two things. One tweet would have alt text attached to its image and one would not. The other difference was that one tweet ended with a black circle emoji and the other ended with a white circle emoji. Because Twitter does not allow identical tweets to be posted at the exact same time, the emoji were necessary. If a test tweet misfired when posting from Sprout Social, both tweets in the set for that day were deleted to avoid skewed data.
In order to eliminate as many variables as possible, which tweet was scheduled first in Sprout Social was alternated every month. Which tweet got the black circle emoji and which got the white circle emoji was also alternated.
For July 2021, September 2021, November 2021, January 2022, and March 2022, the tweet with alt text would be scheduled first in Sprout Social with the black circle emoji.
For June 2021, August 2021, October 2021, December 2021, February 2022, and April 2022, the tweet with alt text would be scheduled second in Sprout Social with the white circle emoji.
The only variables that couldn’t be accounted for with the organic A/B test were people knowingly skewing the test when they figured out which tweet had alt text and which did not. If users had their timelines set to show them tweets in chronological order or by what Twitter’s algorithm recommended to them also could not be accounted for. To offset these variables, three random sets of tweets in the A/B test were boosted to get paid data in addition to organic data.
Impressions: 370,317*
Engagements: 8,509
Average Eng. Rate: 2.3%
*6,021 impressions were
from three boosted posts
Impressions: 352,989*
Engagements: 7,400
Average Eng. Rate: 2.1%
*5,846 impressions were
from three boosted posts
Based on the collected data, social media posts with alt text earn more impressions and engagements and have a higher engagement rate than social media posts without alt text. The full report of monthly data can be downloaded below.
The alt text A/B test was originally supposed to run from June 1, 2021 to May 31, 2022 for a full year of data. However, when Twitter launched its visible alt text badge globally on April 7, 2022, it was decided that it would be best to conclude the test. The visible alt text badge posed too large of a variable to overcome because it would make it too easy for users to knowingly skew the test’s data.
