You're the PM of Facebook Birthdays. Birthday greetings drop one day; what do you do?

Clarifying Questions:

When you say birthday greetings you refer to a drop in people wishing the friends, family or connections on their birthday? 

What is the drop percentage? 

How long is the drop happnening? Is it gradual or something sudden?

User flow

Befor I go ahead and identify the problem I would like to quickly revist the user flow

1. People get registered to FACEBOOK

2. Add profile details and birthday details along with it

3. Save the details

4. Facebook send reminders to friends and Family memebers on the birthday

5. People can tap the notification and add a birthday message with stickers or backgrounds

6. The birthday folk recieves the wish and acknowledges with a reaction or comment

7. Thereby ends with an engagement

Alternative Flow: 

People can go to the birthday section and see for birthdays that are complete and upcoming to wish people

My Hypothesis for this drop

1. Chances are some people might have removed their birthday details from their profiles due to privacy concerns

2. Problem with the reminders e.g. in the notification we see the messages with person x and two more have birthdays today. The person X might not be so relevant for you but the other two might be a close contact. Problems with the reminders suggestions

3. People might opt to send messges  through messenger instead of posting in the time line as a birthday greeting

4. Dicoveribility might be an issue, in devices like iphone you can not find the birthdays product anywhere so people who missed or wanted to wish some one  in advance can find it hard if the product is not discoverable. New users might not beaware of searching for the product

5. If there is a bug then the drop is likely to be sudden and would be more than 50%

6. If the drop is below 20% and happening gradually it might lead to a UX change that has been made recently

7. Increase in birthday events on line or offline may reduce peple from greeting through this product

Data Gathering and Validate Hypothesis

1. Total number of people who removed their birthday details from the profile for the last 2 months

2. Average number of unique messages recived by birthday people on their birthday

3. Number of people tapping the birthday reminders on a daily basis per week

4. Number of people who search for the birthday product per week

5. Was there a product that was recently launched within facebook that has a downstream metric for birthdays

6. Is this specific to a particular region or global? 

Conclusion: From the above data we should be able to come up with a reason on why there is a drop in the numbers and hence our hypothesis also gets validated