When I first started betting on cards, I would often discount the impact the referee could have on the outcome of the fixture. I know, even saying that now sounds silly, but it's the way I used to bet. I would let the statistics for each team drive my betting decisions. Now, that's not the worst way to do things, but you can always dig deeper. Finding a reliable source for referee stats was hard, and I found myself jumping from site to site trying to find consistent data. In the end, I decided to include referee stats into OddAlerts, and I can now get all of the stats I need for betting on card markets from a single place, and for free.
For each referee, there is a detailed breakdown of their recent history, including the ability to view their performance for different competitions. Context and saving time are two of the most important things I think about when developing OddAlerts, so you can find the referee details right alongside the card statistics per fixture. Check this fixture between Manchester City and Brighton as an example. This page also allows you to filter referees for the countries and leagues that they officiate in. To do this, hit the filter icon at the top of the page.
OddAlerts has referee stats for 1,500+ leagues and competitions around the world, from the Premier League to the Brazilian Serie B.