The source of the information is what makes the report reliable, if that source is coming from an government agency or a private intuition which is popular with doing some analytical job, then we can consider it as a reliable one though we can't say it's completely correct. Having this information is important, at least it will give us some ideas on countries where people gamble the most and we can compare the addiction rate to determine if gambling really affect the life of the people when they are gambling.
I don't like the government doing a survey much more on a gambling, they can manipulate this for their needs, I prefer doing it by an independent survey company commissioned by international study companies for compiling data for their would be clients, it's reliable, transparent because they are putting their name on their surveys.
Mind explaining what manipulation would a government do for gambling survey ?
Don't you know that Government are conducting Surveys in everything in each country and not only gambling ,and besides the reason why they need to do this is for the TOURISM ,they are assessing the Gambling industry so the Promotion will be easier and subjectively .
This will generate Funds and also will added growth to the economy .
Private Survey are the one who use for Manipulation ,Look at the Site from OP ,Obviously this was conducted to Favor some Countries for their gambling tourism campaign and not what the real score is.