An oft-repeated legend is that today's cannabis is at least an order of magnitude stronger than in the past (and by implication much more dangerous). THC levels are allegedly 10, 20 or even 30 times higher than in the 1960s or 1970s. Although potency levels have risen in several countries (such as the US and UK), the actual increases have been much more modest (almost threefold from 1982 to 2007 in the US) and high-potency strains have always existed, as have various concentrated forms of cannabis. Furthermore, potency of seized samples was not tested before 1971, leaves were not distinguished from buds by testers at first, and samples from before the early 1980s (when testing and storage procedures were changed) were often degraded, making comparisons going that far back inaccurate. Non-representative sampling was also an issue. Since most of the increase happened after 2000, this legend can be considered an example of ostension (people have been making such claims as far back as the 1970s).