However, where it does exist, it can be a simple and friendly process. An effective step is to speak directly to the nominated FOI officer for the government agency involved. There are also FOI guides, some online, which you can find with a search engine. The reliability of government statistics actually needs some clarifying. Taking the devils advocate position, we can attack any position of presumed integrity.
All statistics can become biased unintentionally.
And in a climate where political purposes can influence the preparation of statistics, we have both the means and the motive. I write this to remind you of bias. I personally find government publications are prone to factual presentation, but occasionally have difficulties with political bias when it comes to conclusions. Perhaps the safe ground in both is a modicum of skepticism and a willingness to untangle the statistics yourself.