Let’s say we want to figure out for any Facebook user, who their best friend is so we can prioritize showing their content in the News Feed. What product signals and metrics (max 5) would you use to determine who a user’s best friend is?

Approach:

1. Ask related questions to understand the prompt better

2. Identify the related signals

3. Prioritize the signals

Clarification questions

Candidate: Can we ignore the new users or users that do not have any friend for the analysis, and just focus on the users that have facebook friends

Interviewer: Yes

Candidate: Can we assume that we want to focus on the people that are non family members for the purpose of this question

Interviewer: Yes

Candidate: Can we assume that we want only consider the people on the friends list becuase it is most best friend is already part of the friends list

Interviewer: Yes

Signals/metrics that can be used to determine the friend

1. Amount of conversation: No of messages that exchanged with the user

2. Group photos: Use computer vision to identify the number of photos where the two are together

3. Neighborhood/school/college/work place: Friends tend to come from the same neighborhood or went to same school or same college or workplace; we can look for commonalites in terms of educational or profession institutions or home towns

4. Similar interests: People can develop strong friendship when they share common interests in terms of technology, sports, movies, actors, foods and common values in terms of politics inclination, religious views, etc. For example, people that are liberal and interested in technology and stock are more likely tend to be friends.

5. Common language: The key thing for developing friendship is language and friends tend to speak/comment things in same language, which would be another indicator

6. Location signals: Friends tend to live together or/and spend time together often especially after working hours and during weekends. Therefore we can track the GPS signals to track the location of users and those that are in close proximity for long period time tend to friends

7. Common groups/friends: Friends tend to belong to same groups and share mutual friends across social media platforms. More number of common groups/mutual friends between two people, more likely they tend to be close friends.

8. Age gap: Most probably, people tend to develop friendships with people they are in the same age group. 

9. Ethinicity: People generally tend to gravitate towards to others that belong to the same ethinic background, since they share similar lifetyles, cultures, values, foods, etc. Race is a another indicator

10. Socio-economic status: People tend to become friends and maintain that friendship with those that fall into same socio-economic status in terms of the job titles, annual earnings, etc. Therefore, job titles could act as a indicator as well.

Prioritization:

I would prioritize the signals/metrics that best predict the level of bonding between the people and are also easy to track/use.

Top five signal in that order

1. Amount of conversation. Communication is key to develop and maintain any relationship, I would track the amount of conversation

2. Location signals: Spending time together is key to maintain friendship I would use this signal as well. 

3. Similar interests: Common interests and values are two pillars for developing strong bonds

4. Common groups/mu: you can find that best friends share more number of common groups between them

5. Ethnic background: Best friends tend to belong to same race

Conclusion:

I would use the signals that are indicators of togetherness to identify the best friend and prioritize their content in the feed. It will help to boost the happiness, connectedness between the facebook users. Hence users would like to spend more time on facebook, driving the engagement with facebook.

Clarifying questions:

• Are there any specific metrics we want to analyze stated by management?

What is Facebook:

• Facebook is a platform with a the mission to create community and bring the world closer together. Some features include adding friends so you can stay connected with people you know on the platform by posting statuses of exciting moments, sharing photos, and direct messaging to get in contact with someone.

How do "friends" engage with one another on Facebook?

• Need to be listed as each others friends
• Post on each others walls
• Comment on each others posts
• React on each others posts
• Message one another

Metrics or product signals to consider:

• Engagement with the user overall, DAU, MAU on and with their account
• Number of Facebook messages exchanged per day, per month
• Number of mutual friends shared
• Number of events they are both going to
• Number of reactions on each others posts per month