National Australia Bank experienced a loss of market share in three key market segments in February and March 2011, but made gains in two, monthly data compiled by the Australian Prudential Regulation Authority shows.NAB is inviting close scrutiny of its market share given the "break-up" theme of its recent marketing campaign, though any shifts in new business and increases in footings (deposits and loans) will become more clear over a longer period than was evident in the APRA data published on Friday.The most noteworthy losses in market share, in the APRA data, are on the business side.NAB recorded a loss of market share on both deposits and loans over the two months to March 2011, as shown in the attached table.The bank also recorded a loss of market share in credit cards.NAB did pick up some market share in household deposits, and most of all in home loans.