From a quick google, then reading some wikipedia then linking the source, it seems its about 5~% of households http://www.federalreserve.gov/pubs/oss/oss2/pape

From a quick google, then reading some wikipedia then linking the source, it seems its about 5~% of households http://www.federalreserve.gov/pubs/oss/oss2/papers/concentration.2001.10.pdf http://www.federalreserve.gov/pubs/oss/oss2/papers/concentra...