A NYT article discussing class divisions in Venezuela included a chart showing an implicit rate of inflation calculated by the Cato Institute. The chart shows an annual rate of inflation of more than 300 percent, compared to an official rate of around 50 percent.
The basis for the difference is that the Cato rate effectively assumes that items are paid for in dollars. As the black market price of Venezuela's currency plunges against the dollar, this leads to a very high measure of inflation. This measure is of dubious relevance to the people of Venezuela, since only a tiny portion of their purchases involve payments in dollars.
As a practical matter, because there are shortages of many items the true inflation rate would be higher than the official rate, since many items cannot be purchased at the measured price. However, the dollar conversion methodology used by Cato is not an appropriate way to measure the effect of shortages. In principle, the correct method would assign a price to the items that are subject to shortages based on their black market price and then weigh them in their proportion to consumers' consumption bundle.