We investigate 306 LASCO front-side halo (partial and full) CMEs from 2009 to 2013, which are well-observed by both the Solar and Heliospheric Observatory (SOHO) and the Solar TErrestrial RElations Observatory (STEREO). These CMEs have two-dimensional (2D) parameters, such as speed, angular width, and propagation direction, from a single spacecraft (SOHO), as well as three-dimensional (3D) parameters from a multi-spacecraft (STEREO). These 2D CME parameters, which are based on plane-of-sky observations, are taken from the SOHO LASCO CME catalog and the NGDC flare catalog. We have determined their 3D CME parameters using the Stereoscopic CME analysis tool (StereoCAT) provided by the Community Coordinated Modeling Center at NASA. We compare 2D and 3D CME parameters, making this the most comprehensive statistical study on CME 3D parameters. As a result, we find that 2D speeds underestimate the 3D speed by about 20%. The 3D width ranges from 30° to 158°, values which are much smaller than the 2D widths with a mean value of 225°. We also find that the ratio between the 2D and 3D widths decreases with central meridian distance. The 3D propagation directions are similar to the flare locations, with a mean absolute difference of about 13°. The width-speed relationship in 3D is much stronger than that in 2D.
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