Determine the right number of photos to show in Facebook's newsfeed.

Context

First off let's just get on the same page by establishing a common understanding of just what the Facebook Newsfeed is and how users use it. Facebook's Newsfeed is the first thing users see when they log into Facebook on both mobile and desktop. It is a continuous scrollable feed of what has algorithmically been determined to be the best most relevant and interesting content from around that user's network. It shows a variety of content like photos, videos, Facebook groups, people you may know, and ads in the form of posts. Users may also interact with these posts by liking, commenting, or reacting.

To better frame this question and understand the role Facebook Newsfeed plays in the bigger picture, it's good to examine it in the context of Facebook's mission statement which is to bring the world closer together and give people the power to build community. Newsfeed helps further this mission statement by making it easy to consume content and stay up to date on the lives of those you are close to. Similarly it makes it easy for your friends to consume the content you share.

Goal

At it's core the Facebook Newsfeed's purpose is to primarily drive engagement and by extension retention. The content in the Newsfeed is captivating thus motivating users to keep scrolling and to check back later for more new content. It is addicting, have you ever closed out a FB tab only to absent mindedly instantly re-open it again in a new tab?

A few metrics we could use to monitor Newsfeed's ability to engage and retain users are:

1. Average number of posts viewed per session

2. Average newsfeed session duration

3. % of users who had 3 or more sessions last week where they viewed at least 10 posts who also had 3 or more similar sessions this week

Trade Offs

Like most features, showing more photos in the Newsfeed doesn't have an entirely positive or negative impact. Let's go ahead and brainstorm what some of the potential tradeoffs could be for increasing the amount of photos shown in the Newsfeed:

Pros

-Photos are easier to consume than other posts -> Increased number of posts viewed

-More overall interactions with photos will encourage users to upload and share more photos

----Larger training set for our visual ML models

Cons

-Run out relevant photos to show -> Interaction rate and engagement goes down

-Less airtime with other post types like videos will lead to less interaction with them and declined usage over time for those post types as that feedback loop is dampered

-Users who don't post photos will receive less interactions and their engagement will drop

Near Term

If we were short on resources or needed to come up with an answer ASAP, I would propose we perform an A/B/C test where each testing option is applied to 1% of Facebook's users. This % is small but Facebook has a large number of users so each sample size should be sufficiently large. Based upon which bucket they are in these users would either see a photos in the Newsfeed every 5, 10, or 15 posts. We would then monitor and compare the following metrics to help use decide which frequency is best:

1. Average number of posts viewed per session

2. Average newsfeed session duration

3. % of users who had 3 or more sessions last week where they viewed at least 10 posts who also had 3 or more similar sessions this week

Longer Term

Ultimately, I would like to take a more nuanced approach where we decide whether or not to show a photo in the users Newsfeed based upon a model incorporating several factors instead of a totalitarian approach where a photo is showed every x posts no matter what. Several of the factors that we could consider:

1. Users affinity for photos - some users may like or interact with photos more than others

2. Relevancy of photo subject to the user - A user who is a musician would be more interested in a photo of a guitar than someone who is not musically inclined

3. Closeness of the use to the poster / tagged users - I would be more interested in a photo of my sister than someone I had a group project with in college 10 years ago and haven't spoken to since

4. Amount of photos the user has already viewed - Do they have any fatigue related to having already been shown a lot of photos?

5. Relevancy of competing posts - I think this is a large factor. The question is less about should we show a photo next, but more so about what should we show next period? The relevancy of other potential posts to the user would play a big role here. If their best friend just made a post that is probably more important than whatever photo is up next.

It would take a lot of time and we would need to work closely with the data science team to quantify and analyze how  these different variables affect engagement on photos in the Newsfeed but for such a critical core feature of Facebook I think it would be worth the effort.

Summary

Facebook's Newsfeed helps users consume relevant content from around their network. In order to figure out the optimal number of photos to show in the feed to users we could perform an A/B test with varying levels of photo frequency and then measure their impact on key engagement and retention metrics. Ultimately, we could work closely with our data science team to to build out a model for deciding whether or not we should show a photo in the user's Newsfeed based upon a variety of relevant factors.