The crime statistics police released in September are flawed, the Institute for Security Studies (ISS) said on Wednesday.
They contained a "serious statistical error", ISS governance, crime and justice division head Gareth Newham said in a statement.
"The effect of this miscalculation is that it downplays the extent to which certain serious, violent crime categories are rising in South Africa, while exaggerating those categories that are decreasing," he said.
"What we are asking is why did this error occur, and at what level was it sanctioned?"
The errors were a result of inaccurate population figures being used to compare the change in crime ratios between 2011/12 and 2012/13.
The ISS said it had called for a formal independent inquiry into why the trends were miscalculated. The miscalculation was more pronounced when it came to determining crime trends at a provincial level, it said.