Immigrants are more likely to remain in Alberta and Ontario but leave the Atlantic provinces

In 2014, 87% of immigrant taxfilers who landed three years earlier filed taxes in the province where they had landed. The proportions were the highest in Alberta (92%) and Ontario (91%). The Atlantic provinces had lower retention at 53%. The rates were over 80% in British Columbia (88%), Saskatchewan (84%), Quebec (83%) and Manitoba (82%).

Can one assume that all immigrants are tax filers and how can our government check out the figures  so 'accurately'