  A sample of 427 gamma-ray bursts (GRBs), measured by the RHESSI satellite, is
studied statistically to determine the number of GRB groups. Previous studies
based on the BATSE Catalog and recently on the Swift data claim the existence
of an intermediate GRB group, besides the long and short groups. Using only the
GRB durations T90 and chi^2 or F-test, we have not found any statistically
significant intermediate group. However, the maximum likelihood ratio test,
one-dimensional as well as two-dimensional hardness vs. T90 plane, reveal the
reality of an intermediate group. Hence, the existence of this group follows
not only from the BATSE and Swift datasets, but also from the RHESSI results.
