Tanin, EgemenLotem, AmnonHaddadin, IhabShneiderman, BenPlaisant, CatherineSlaughter, LauraCurrent network data exploration systems which use command languages (e.g. SQL) or form fill-in interfaces fail to give users an indication of the distribution of data items. This leads many users to waste time posing queries which have zero-hit or mega-hit result sets. Query previewing is a novel visual approach for browsing huge networked information warehouses. Query previews supply data distribution information about the database that is being searched and give continuous feedback about the size of the result set for the query as it is being formed. Our within-subjects empirical comparison studied 12 subjects using a form fill-in interface with and without query previews. We found statistically significant differences showing that query previews sped up performance 1.6 to 2.1 times and led to higher subjective satisfaction. (Also cross-referenced as UMIACS-98-14)en-USTechnical Report