These labels will appear in the tool tips section of the reporting table and in the customise column selector for ads in Facebook, Instagram and Audience Network.
The goal is to help advertisers determine how much weight to place on the metrics.
Metrics labelled as "estimated" are calculated based on sampling or modelling.
These metrics provide guidance for outcomes that are hard to precisely quantify. Real-time results, for example, are among those that rely on sampling methods that allow people to instantly model metrics at scale.
Reach too is an "estimated" metric as it relies on sample data. Facebook analyses the number of people who see an ad multiple times, de-duplicates them and then calculates the total number of unique people in real time. To do this quickly, Facebook samples the data and will therefore label it as estimated. This is also how reach is calculated for ads on TV and across other digital platforms.
"By labelling metrics as estimated, you will now know when these methods are used," Facebook said in a statement.
Metrics labelled "in development" may be new or in testing, and so may evolve.
An example is "estimated ad recall lift". A metric used by brands to understand the differences between people who can recall a brand after seeing an ad compared to those who have not seen an ad. This type of measurement is still new for Facebook and requires a combination of polling and machine learning.
"Because we use sampling to determine this metric, it will be labelled as estimated, and since we're still gathering advertiser feedback on it, it will also be labelled as in development," Facebook’s statement explained.
In July, Facebook will remove around 20 ad metrics that marketer feedback has indicated to be redundant, outdated, not actionable or infrequently used.
One example is the social reach metric which shows the number of people who saw an ad with social information above it. Marketers, however, find that this metric isn’t meaningfully different from the reach metric, and that the insight drawn from it doesn't indicate a business outcome.
Facebook will also be embarking on a programme to help businesses understand how best to measure outcomes. The "Measure What Matters" programme will start in March and will offer two tracks – one for advertisers focused on brand objectives and one for advertisers with direct response objectives. Each track will run through in-person events, Facebook Live events and on the Facebook Business website.