Method
Comparing AI visibility periods without mixing samples
To compare two periods, the engine, the collection method and the prompts must match. If any of them changes, you are looking at a different sample, not a shift in AI visibility.
There is one rule for comparing two periods without mixing samples: only compare when the engine, the collection method and the prompts are the same. If any one of those three changes, you are no longer comparing the same sample. In RankAI, AI visibility is measured from what an engine returns through an API. That is the API response, not the screen a person sees. When a measurement is not available, we show it as N/A, never as zero. The same applies when the engine stays the same but the API version changes: rebuild the comparison instead of forcing it.
Defining conditions you can compare over time
A comparison between periods is only useful if the conditions of observation stay stable. In our working approach, before you read a change, ask whether the engine queried, the method used to collect the data and the set of prompts all stayed the same. If one of them is missing, the figure may look different for reasons that have nothing to do with visibility. That is why, when a measurement is not available, we mark it N/A: an absence is not a zero and should not be treated as one.
The RankAI method for comparisons over time (a working approach, not a universal standard). Before comparing two periods, check in order: (1) the same engine was queried; (2) the same collection method was used, meaning the same API route and the same declared version; (3) the same set of prompts was used, with nothing added or removed between the two periods. If any of the three does not match, the comparison is not valid: rebuild the sample instead of reading the difference as a change in visibility. If the engine is the same but the API version has changed, treat the period as a new sample and do not combine the data. When a measurement is missing, it stays N/A: it must not be turned into zero or included in averages or totals as if it were an observed value. This method exists to keep changes in the tool from being mistaken for changes in AI visibility.
An illustrative example
Suppose, purely for illustration, that you have two periods with the same engine and the same prompts but a different API version. In that case we do not read the difference as a change in visibility: we treat it as a change of sample. If the engine, the method and the prompts do match, the difference between the two periods can be compared. In both cases, missing measurements stay N/A and do not enter any calculation as zeros.
A limit you can check
The limit is verifiable: if you cannot show that the engine, the method and the prompts were identical in both periods, the comparison is not valid. RankAI does not fill gaps with estimates: missing measurements stay N/A. For the full picture of how measurement works, see the in-depth page.