The reason for the data to be unreliable is that the survey has been done between the year 2000 and 2007.The survey was done many years ago and this data cannot be used as it can change every year.
It cannot be considered factual as the data is very old. A huge change in the number could have occurred.
The number of individual getting involved in drugs are increasing day by day so a data that is 10 years old will not be feasible.