Not all combinations of dimensions and metrics make sense in a Google Analytics report. Choosing to show a hit-level metric alongside a session-level dimension in your custom or filtered reports isn’t something you’re restricted from doing, but in many cases the results in your report won’t make sense.
Worse, when you’re viewing the report, you may not even recognise a problem, as numbers that look like real numbers will still be displaying and updating.
Google Digital Marketing Evangelist Avinaush Kaushik’s blog post here explains the mess you can make of your reports by mismatching metrics from one level with dimensions from another.
The problem is, when you’re searching via the dropdown in the reporting interface, metric names alone aren’t always enough to tell you whether that ostensibly perfect metric you’re about to include in your report is a hit-, session-, or user-level metric.
Google Analytics is a complicated beast.
The Dimensions & Metrics Reference is the official Google Analytics source for looking up valid combinations.
This page lists dimensions and metrics within categories like User, Session, Traffic Sources and so on (all the ones you see in the Dimension dropdown in the reporting interface). Check the one you’re interested in like so:
- Use the first set of radio buttons to choose between API mode or the UI Names mode. UI Names mode shows user-friendly versions of the names which is nice. API mode doesn’t show these but has a more immediately-understandable column-based UI. Choose your poison—probably the UI Names mode.
- Click the ‘+’ icon corresponding to a category to expand it.
What you’ll see now is two lists. If you’re viewing in UI Names mode, one will be on top of the other. If you’re in API mode, the lists are alongside one another.
- Either way, the way to see what metrics can be used in valid combination with a dimension is to select the checkbox beside a Dimension. (Don’t click the word itself: doing so takes you through to a detailed view of the dimension in the API.)
The Metrics that are valid in combination with this dimension will remain displayed in the corresponding Metrics list, while those that aren’t valid will be greyed out.