This is the third of a three part series detailing the key topics that institutional investors are talking about on Facebook (FB). Facebook will report earnings on Wednesday, November 4.

Part 1: Detailing FB's Near-Term Revenue Drivers

Part 2: Detailing FB's Longer-Term Revenue Drivers and the Bear Case

Part 3: What Investors are Focused on Ahead of FB's 3Q Results

The Key 3Q15 Items to Keep an Eye On

With the bull and bear thesis fleshed out, we can now take a look at expectations heading into Facebook's 3Q and which line items are most crucial for each side of the argument.

Have you ever seen a company beat consensus EPS estimates, but the stock still goes down? This happens because institutional investors focus on many other line items besides earnings. Here are the key issues (beyond the obvious EPS estimate of $0.52) that investors will be focused on:

- Advertising Revenue. This is the key metric for Facebook's core advertising business. Wall Street analysts are generally looking for advertising revenue growth of ~40%-43% y/y growth, with potential upside driven by video and Instagram. Analysts will also be looking for positive commentary around how these two factors impacted advertising revenue.

- 2016 Expense Guidance. As I detailed yesterday, a near-term  concern is that Facebook may give 2016 expense guidance that is above the Street's current expectations. Investors will be watching to see if Facebook management provides guidance/commentary on expense expectations for next year (which also may not come in this quarter at all, as the company generally gives guidance in 4Q). Wall Street analysts generally expect 2016 expense growth of ~40%, but some investors fear expenses could potentially come in much higher than this.

- User Growth. User growth is one of the primary drivers of advertising revenue. Analysts are expecting continued user growth of around 12% y/y.

- User Engagement. Again, as I detailed yesterday, a big part of the bear thesis is a decline in user engagement as users flock to competing social media platforms like Snapchat. Investors will be watching user engagement closely, measured in terms of the percentage of monthly average users that log in daily (DAU divided by MAU). Generally, Wall Street analysts expect the metric to remain around 65%. 

- 4Q Revenue Commentary. Facebook's general guidance for revenue was for continued deceleration in 3Q and 4Q. Investors will be looking for any additional color on expected revenue trends in 4Q, with any sign that management is trying to temper expectations likely interpreted as a negative by investors.

Intraquarter Datapoints

Analysts and investors received a number of datapoints from a variety of sources that offer some window into what Facebook might report. The following are the key datapoints that investors noted: 

- Facebook provided several datapoints in the quarter on Instagram, noting that 1) Instagram had reached 400 million users, and 2) that users may begin to see increased ad loads.

- Google's earnings results provide some readthrough on the health of the online advertising industry. Their 3Q results were particularly strong with organic ad revenue growth of 21%, which bodes well for Facebook.

- Industry data providers were somewhat mixed to slightly positive. Nanigans, Comscore, and Kenshoo all reported positive trends that suggest strong social advertising spend at Facebook, while RKG and Ignition reported trends that suggested some deceleration in 3Q advertising spend. 

- Anecdotally, numerous analysts noted higher ad loads on Instagram, which would suggest a positive contribution to advertising revenue from the platform.