A Data-driven culture is an output metric
in a sense. If you try to measure the degree to which people use data in their decisions, the number of users of your BI tool, etc., all of these come down to output metrics.
If you truly want to drive up data-driven decision-making inside your company, you cannot focus on any of these numbers.
Instead, you need to find the controllable inputs, the metrics that
can be influenced by you, and
have a measurable impact on your output metrics.
One way to get people to use data is to create an environment where it’s better for them to do it! So, if you want to create a data-driven culture, you must:
Make sure the right data people need is always available,
the data is easily (and I mean as easy as the pen on the table!) available,
and everyone knows exactly that this data helps them make a decision.
Those three asks are about removing impediments and education, things you can very much influence, and much closer to input metrics than the output metrics above.