Understanding the difference between dimensions, metrics and criteria is a little tricky at first. The following explanation will walk you through these three aspects that are required when creating a report.
Criteria are the actual data aspects that give your filter it's functionality. As mentioned before, one of the first steps in creating a custom report is defining the relevant filter that will be displayed at the top of your report. Criteria give that filter it's functionality by defining the data context of what you are looking for in your report.
Note: Criteria are generated automatically by the system depending on the filters you select.
The best way to describe Criteria is using the following example:
Let's say you want to create a report for your company that will show how many Video Views each video you uploaded has obtained.
To do this we will need to select the 'Company' filter for your report, but still, your filter doesn't know at what companies. But now, you realize that your company has several affiliates. Some are Content Owner companies that are used to upload videos and some are Publisher affiliates used to embed players. How can you choose which ones to select for your report. This is where Criteria can help you. Using the criteria selection you can choose if you want to see just the seller companies (Content Owner), just the buyer companies (Publishers) or both. Using criteria you can point to the specific aspect of your selected filter. In other words, the criteria field assists the selected filter to determine what exactly you want to point to in your report.
Metrics are the actual numerical data that is accumulated and stored in our system. In regard to our example above, we would now like to select Video Starts and/or Video Completions or any other measurable data to be used in our report. By selecting these values you are actually defining what data you want to view.
Dimensions are the last piece of the puzzle. Dimensions are aspects used to slice your metric data. In regard to our example, we would like to slice the Video Starts and Completions according to a Video Name and/or ID. This will aggregate all the data accordingly so you can see exactly how many views each video under your selected company has obtained.