Serial Position Effect: Why Order Matters in Optimization

Serial Position Effect: Why Order Matters in Optimization

You put tons of time into creating your product, experimenting with acquisition channels, honing your messaging—and here I am, about to tell you that consumers are often swayed by such a subtle thing as the order in which you present your products, or the “serial position effect.”

It’s a funny thing, human behavior.

Often, small nudges can produce significant changes in how we act. The serial position effect is one such behavioral nudge. It has interesting implications for memory, preference, and behavior and, of course, for designing and optimizing your website.

Serial Position Effect and How It Affects Memory

The serial position effect is the tendency of a person to remember the first and last items in a series best and the middle items worst. It’s made of two parts:

Primacy and Recency Explained

Primacy: Things that happen first are typically the most important because they influence what comes next.

The theory behind primacy effect is that there is a relatively small amount of processing effort expended in rehearsing the item by itself. So, basically, when you process the 9th item on a list, you’re also processing the previous 8, where the first one is by itself. This results in greater cognitive fluency and therefore greater recall.

Recency: Things that just happened are relevant because they are the most accurate representation of “now.”

The theory behind recency effect is that items at the end of a sequence are easier remember because of their preservation in our working memory (the part of our short-term memory that processes conscious and immediate perceptual information). Our working memory only holds ephemeral information. It acts as a buffer for new information while it processes it into other, longer-term memory systems.

All that stuff in the middle? That’s likely to be forgotten. Even if people read everything, the stuff in the middle would be the most likely to be forgotten.

The effect Primacy and Recency have on recall is powerful and well studied. It’s not a new concept, at all. Apparently Hermann Ebbinghaus (1850-1909) originally coined the term ‘serial position effect’ after conducting a number of memory studies on himself.

Then this study from 1962, where researchers analyzed free recall of word lists ranging from 10 to 40 words, supported the effect. Here’s a chart of the results:

As you can see, the last words on the list are much more likely to be recalled. Similarly, as the lists get longer, it becomes increasingly unlikely that subjects remember the middle words (as well as the first words).

List Order Matters – What’s Optimal?

One other finding with the Serial Position Effect is that, if there is a “distracter task” between the information study phase (the list presentation) and test phase (when respondents are asked to recall), Recency Effect will fade in power.

However, in the study, Primacy Effect was still present after a 30-second interference task. From the study, researchers concluded that the capacity of human short term memory is likely to be three to four chunks of information at one time.

Be aware of the Serial Position Effect when presenting visitors with a list – of any kind (a set of links, sales pitch, a feature list, client list, navigation, etc.)

Baymard gives some advice regarding lists on your website, all good ideas to consider:

  • Put the least important items in the middle of the list, and the most important first or last. As a commenter on the Baymard article said, “I use this effect to add at the end of the list (so bottom of the list) the main attractive item (ex. North European who prefer the South of France) because I know that the users will go to the last item and I know that they will read the first too.”
  • If the prospect makes a decision greater than 30 seconds after exposure, place the most important item first. If the decision is made right away, place the most important item last on the list (this has to do with the time of exposure part of the Serial Position Effect). The example they gave: On a sales page, try putting the main benefit first on the list, and list persuasive extras like “free shipping” and “works with iPod”, last. This way if the subject leaves the page they are more likely to remember the main benefit of your product.
  • When the user doesn’t set the pace of the presented items, such as in video and audio, present the most important items last (and first, might I add – especially as they’re probably not going to make it all the way through the media).

Primacy and Anchoring Effects

We’ve talked, in previous articles, about the power of defaults. Users don’t like to exert any extra effort, so they tend to go with the option with the least friction. Often, this is the option that is most prominent or memorable. Serial Position Effect can aid in this process, especially in regards to pricing.

We published an Academic Insight that looked at two ways of presenting product information:

  • Product primacy
  • Pricing primacy

Product primacy is when the subject sees the product first, and then later the price; pricing primacy is opposite – price first (say you walk up to a rack of $40 shirts at a department store then see the shirts). The researchers found:

  • When consumers see a price before the product, they evaluate the product’s worth more critically.
  • When they see the product first, they evaluate the product solely on that criteria.

Essentially, what the consumer sees first sets an anchor by which they judge the entire experience. How can you use this to your advantage? Perhaps with SaaS pricing pages, you can set the highest price first, like Crazy Egg does:

Screen Shot 2016-06-07 at 3.40.56 PM

Or, similarly, you could test the order of your products on a category page:

Screen Shot 2016-06-07 at 3.46.28 PM

You might notice this price anchoring when at a nice restaurant. Restaurant consultants often suggest adding a super expensive wine or menu item and featuring it prominently, so everything else looks reasonable in comparison.

Know, however, that prototypicality is the balancing force here. Users are used to seeing increasing pricing order (lowest first). And if they’re comparison shopping (they are), seeing the highest price first could be a source of friction.

There are always examples that contradict the best practices, so what works for someone else may not work for you. It’s always contextual, right?

Studies have shown people most often choose the first bubble gum in a sequence, but if you’re selling real estate, it seems to be most effective to show the consumer the most applicable property last.

Point is, order can make a big difference and it’s not a difficult test to set up.

Order Affects Your Preference

Another interesting characteristic of order is that it actually influences consumer preference. A study published in 2007 explained these effects clearly.

The researchers studied “recommender systems” – systems that help consumers choose which product to buy.

Subjects were shown randomized variations of tent order. All the tents had different features – waterproofing, closures, etc. – yet consumers chose the first tent over the rest by a factor of 2.5X, no matter what the first tent was.

If you’ve ever sent out an email newsletter, you know the order matters. People click more on the first (and last) links.

With ours, for example, we feature content from the blog that was published the last week. We consistently find the most traffic going to the first one we post. Therefore, we try to feature a post that has already shown signs of organic traction to give it a boost:

Screen Shot 2016-06-07 at 3.20.06 PM

Other newsletters, like Instapaper, organize by popularity as well:

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Join the Conversation Add Your Comment

  1. Like the article and it all makes sense. When you are building such product pages you sometimes need to put micro-copy that are visible on hover. If you want to A/B test the micro-copy how do you quantitatively determine which microy-copy is better? Even if the user completes the goal of the page more for micro-copy B, there is no certainty that micro-copy B made the difference.

    1. Alex Birkett

      Sounds like something you’d need lots of traffic for to detect any effect. But if you isolate the element of microcopy, you can infer that it’s what made the difference. Seems like a very small thing to test though, but if you want to read more about micro-copy, Tommy wrote a fantastic article on it a while ago:

  2. The two key takeaways from this article you can take to the bank with my experiences sprinkled in:

    Have one option in your sales process, either on your site or on the phone that is way way higher than the one you really want to sell, and I can guarantee you can raise your pricing on that option you really want to sell.
    If users will always buy more of the left facing item, you can either up the price on that item container by 10% until you find a profitable sweet spot using an algebraic formula or make sure to just stick your product with the sweetest margins left as a part of your sites sorting algo as this article eludes to.

    1. Alex Birkett

      Thanks for the comment!

      To your point #1, it’s amazing how a few $30+ cocktails on a menu can make a $10 beer look cheap :)

      And point #2, yeah the first item will usually get more attention (not always more purchases), and optimizing revenue is important. But to Roger Dooley’s suggestion above, it’s probably best, long term, to emphasize the best-fit product (one which offers the best combination of value and performance). Best chances, from a CX standpoint, to get those repeat purchases.

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Serial Position Effect: Why Order Matters in Optimization