From the user's perspective, a carousel is just a random image. You'll get more conversions if you choose the best image instead of a random one.
http://www.bayesianwitch.com/blog/2014/carouselsarebadforcon...
If I'd get to redo the public website of our research institute, I'd add a carousel, because it looks cool and modern, and it allows you to showcase the work of different people without favoring one person by giving them the "best space".
And even if you have something to sell, it might be valuable to "wow" your potential customer, and to give them the impression that you are "cool" and "modern" and "state of the art" and have moving pictures of happy pretty professionals on your site.
Or, it might be better to have a big "BUY" or "DOWNLOAD" button in that space.
You can't generally say what's better for all use cases IMHO. You got to understand your visitors/customers, do testing if you can afford it, and so on.
Also, the main reason why carousels suck in my opinion, the bad usability (no touch, unclear if clicking moves to the next picture or opens another page, not clear how to move to other pictures) seems to be fixed nicely buy this script.
Probably one of the most undisclosed facts about the schools website: beyond students using it, they probably tested the hell out of "does it drive donations"
Even nonprofits* have conversions to worry about - they take in donor and grant money. Making sure the site is clear in order to do so is way more important than cool
*I can actually name a few nonprofits that do not have this model, but thats because they are secretly for profits if you look through their budgets. They tend to exist in sectors providing services on behalf of the federal government to say the disabled. They don't need to worry about conversions.
Essentially a carousel gives you a "second-bite" at your customer, i.e. the second image is a chance to convert those customers who haven't already been converted by the first image.
Imagine you have two images one which converts at 40% and one which converts at 20% - but each image converts completely different groups; by carouseling the images you could end up with 40%+20% conversion.
In practice you won't because of overlaps, drop-off from people who never see the second image, etc. but it's definitely possible to exceed the maximum conversion of an individual image.
(obviously you should A/B test for your circumstances)
It is totally possible that there are edge cases where we are wrong. While we’ve personally performed split tests between carousels and their elements and always came up with an individual slide (rather than the whole carousel) as the highest revenue generating source, it is possible that there will be some cases where a carousel is better for conversions.
To go with your example, assuming each group has 50%, it's still tough. The actual conversion rate of the carousel in your example will be T x 60% + (1-T) x 30%, where T is the fraction of users who actually wait for the second image. Some simple algebra suggests that for this to exceed 40%, you'll need T > 1/3.
A good intuitive way to think about it is this: if you're only showing the second carousel image to people who the first image failed to convert then there's zero down-side.
In practice there are some users who would convert if shown the first image for longer who you'll lose by rotating to another image, but that's what you need to measure to decide if it's worth having a carousel.
I don't think we really disagree - you should test the carousel, and cases where it wins will be edge cases usually.
In an ideal world, what you should do instead is parametric optimization of some sort instead of a carousel - so you can hit that other 20%
I've personally never seen carousels out-perform alternatives like having multiple images on the page, or multiple landing pages with separate messaging, or just dropping multiple options for the one that's most important.
I'm sure that there are some cases where they're an effective option - but I've yet to come across one in testing.
As Brad Frost once observed "Carousels exist to keep people from beating the shit out of each other in meetings." - https://twitter.com/karenmcgrane/status/316563205294010370
And sometimes "people" is just the different people in your head who want to talk about ALL THE THINGS - when talking about just the most important one is what you really need to do.
"Don’t Use Automatic Image Sliders or Carousels, Ignore the Fad" http://conversionxl.com/dont-use-automatic-image-sliders-or-...
Product recommendations on e-commerce sites, Alternate images of products, galleries on mobile, etc...
Plus, good UX or not, I haven't had a design hit my DropBox in over 5 years that hasn't had a carousel in it. So if you have to use one, use this one.
Website Manager: "Okay, we'll put you in the carousel."
http://www.wellingtonstravel.com
I built mine myself but the slick carousel looks pretty good!
In our website we use it for instructional photo succession, I think it works pretty good, I'm open to suggestions (other than videos) to other UI elements that would work better for that that purpose.
If you want to see a really horrible example of that kind of politics getting in the way of customers and users - SearsCo
For example if you are showing let say showing a set of different products, carousel is a bad choice. Because it is dependent on interaction by user or the possibility the user stays on the page long enough for carousal to change image.
But if you are on the product page and viewing different angles of the same product. The bigger the image better the conversion. In this case we have found carousal can help. You still can not use carousal without thumbnails. Thumbnails create 3 times more interaction compared to Carousal. So to summarize for us at Bryght following is true.
Carousal Only < Thumbnails Only < Both Carousal + Thumbnails
Here is the example of product page we are currently experimenting:
http://www.bryght.com/product/854/long-island-brown-leather-...
Carousels as a component are useful for a lot more than just homepage slideshows :)