“Explore best practices in playlist size: What’s the optimal number of messages for audiences? There is no one size-fits-all solution, so how are system owners handling this?”
My recommended approach would be as follows: First, settle on the average dwell time of the audience, that is, how long a viewer typically watches the screen/s per visit. Second, I would take into account the average return rate of the audience, that is, how often the audience returns to the screen/s. Lastly, I would consider the desired frequency per message type within the playlist.
Dwell Time: Naturally, should the Dwell Time be longer, the playlist length should follow suit. Most system owners will use this variable alone to identify the length of the playlist. Logically, this makes sense. Any less messaging and the content will repeat causing the audience to lose interest. Any additional messaging will be missed by some of the audience and will cause your viewership numbers to be inaccurate while also being wasteful to the content budget.
Tip: You can identify the Dwell Time by taking a sample size of your network and doing some manual Market Research (hiring a third party Market Research company would be most legit) or using numerous automated software options out there that track eyeballs and bodies in front of your screen.
Return Rate: Consider the frequency by which the audience will return. A mall may have an average return rate of every two weeks, a doctors’ offices may not see a visitor return on average for six months and a corporate communications network by the water cooler could see their audience returning four times a day. The point is that the playlist size should not be considered alone as it is insufficient to encompass the best practices for identifying the “optimal number of messages” pushed to your audience.
Effective Frequency: How often should each message be seen by your audience? While an important HR message should desired to be seen by every employee at least four to seven times to ensure the message is clearly delivered (not counting other communication mediums), a news story would feel old having been seen numerous times and should therefore feel as if it was a new story every time the audience returns. Or, in the case of the Mall, where the Return Rate may be two weeks, an advertisement could stay up for two months and be good while news or weather ought to feel as if it was updated in the last 15 to 60 minutes. Effective Frequency also comes into play regarding the “optimal number of messages” as a system owner may desire to show the same message multiple times within the same Dwell Time, making the number of total messages within a single playlist less.
In short, you can simply use the dwell time measurement to identify the number of messages included in a playlist making up the total playlist size. However, there are many other factors to consider, even beyond these three mentioned, to decide how often those messages should be updated and what the optimal rate of playing those messages within the playlist might be.
Truly, there is no one-size-fits-all solution (as the question has stated), and each network, or maybe even every screen, should be strategically and continually be analyzed for optimal performance of the content budget thereby maximizing the ROO of the network.