How much research has been done on flipped learning? The 2022 (and final?) update

In case you haven't noticed, this blog has been on the back burner for a month or so. That's because David Clark and I are in heads-down mode to finish our book Grading For Growth which should come out in 2023 and whose manuscript is due in <checks notes> less than two months. Most of my public writing is happening over at our companion blog, gradingforgrowth.com (and at some point I'll cross post those here... maybe) as practice runs on stuff that will eventually appear in that book.

But there's one summer blogging tradition I can't yet give up, and that's the annual update on how much research has been done on flipped learning. This was something I started doing six years ago, while I was working on my first book. I was doing the literature review and simultaneously fielding questions about how much research was out there supporting flipped learning. Definitely not all of those questions were in good faith. But I needed to do a lit review regardless, so I let that question guide me.

I've updated that post each year ever since, in mid-summer using data from the previous year, to check the pulse of the ongoing phenomenon that is flipped learning. Let's take a look back at how things turned out in 2021.

The way I gather data to answer this question is crude and full of holes, but simple: I go to the ERIC database for education and do this "advanced" search using this query:

(title:"flipped learning" OR abstract:"flipped learning") AND (pubyear:2021)

This brings back all the papers that were published in 2021 that have "flipped learning" in either the title or the abstract. Additionally there's a checkbox, which I select, that gives you only the peer-reviewed articles. Then I do a second search using "flipped classroom" as the search string, then a third one using "inverted classroom". I total up the number of hits from each of those three searches, and that's the number I use: the number of peer-reviewed articles from 2021 with flipped learning, flipped classroom, or inverted classroom – in my experience, the three most commonly-used terms to describe this concept – in either the title or the abstract.

As I said, crude and lots of holes: It double-counts articles where a search term appears in both the title and the abstract; it doesn't count at all any article that might refer to flipped learning by some other term (I've seen a few alternatives), and undoubtedly more. But it's quick and gives an overall sense of the landscape, and it's easy to reproduce by anybody.

I wasn't sure what to expect from 2021 before I did the update this year. After a slump in 2018, the numbers rebounded in 2019 and 2020. On the one hand, momentum seemed to be building. On the other hand, 2021 would be the year you'd typically see papers published from studies conducted in 2020, and we all know why those numbers might be down.

Here's how the numbers stack up for 2021:

Search term Publications in 2021 Difference from 2020
Flipped classroom 151 -40
Flipped learning 78 -5
Inverted classroom 6 + 4
Total: 235 -41

I added this to the ongoing spreadsheet I keep with the yearly data in it:

As you can see, this puts 2021 at almost the same level of research output as 2019.

Of course, the cumulative amount continues to grow (because that's what accumulations do):

The data point for 2021 didn't show up in the chart but it's 1383.

And finally, here's what the cumulative data look like with a regression curve though them:

The exponential model is $y = 0.741132 \cdot 1.44742^t$ where $t$ is the number of years since 2000, and the r-squared on that is 0.9847.