Merge pull request #595 from plausible/minute-interval-faq

Add minute interval graph explanation to Dashboard FAQ page

Author: RobertJoonas

docs/dashboard-faq.md

@@ -16,6 +16,21 @@ This is why adding up unique visitor numbers and comparing them to the total is
 
 There's another situation where differences might occur. If you manually tally the unique visitors for each day in a month, you may not get the same result as the number of unique visitors you see in the report for that month. This discrepancy is due to sessions that overlap with [our daily reset](https://plausible.io/data-policy#how-we-count-unique-users-without-cookies). Consider this: If someone visits your site 5 minutes before our daily reset and they continue being engaged with your site until 5 minutes after the reset, their session will count as one unique visitor on each of the two days. However, in the monthly view, that visitor will be counted as one unique visitor only.
 
+## Unique visitors or Total visits greater than Pageviews on a minute-interval graph?
+
+On minute-interval graphs (such as the realtime dashboard), we count visitors and sessions based on whether their session was active. However, pageviews are counted in each time bucket where they actually happened.
+
+Let's bring a simple example to understand this. Imagine there was only a single visitor who:
+
+* landed on your website on 12:00 (first pageview)
+* spent 10 minutes viewing the first page
+* navigated to another page on your website at 12:10 (second pageview)
+* left your site
+
+Now if we focus on a specific minute on the graph like 12:05, there were no pageviews, but there was a session active during that minute. This is where Plausible would report "Unique visitors" (and "Total visits") as 1, while "Pageviews" is 0. Therefore, the number of visitors and visits is always higher than pageviews when we start summing the numbers up in minute buckets.
+
+Note that this doesn't affect graphs with an hourly (or greater) interval. A session is ended automatically with at least 30 minutes of inactivity. This guarantees that there cannot exist an hour where a session was active, but didn't send us any pageviews.
+
 ## Does Plausible exclude known bots and spam traffic?
 
 Plausible excludes bots, crawlers, referrer spam and other known non-human traffic by default. In [a test we ran](https://plausible.io/blog/server-log-analysis), we saw 18x more pageviews with server side tracking than with Plausible Analytics which shows the volume of spam traffic that Plausible excludes.