Updated at 5.46pm: About 22,000 officers, wearing grey vests and carrying red satchels labelled with the census logo, will visit 310,000 households from March 15 to 27, the Census and Statistics Department said on Monday. Department Commissioner Frederick Ho Wing-huen said the $550 million project would involve everyone - even non-residents working in Hong Kong. The officers, mostly senior secondary students, will quiz one seventh of Hong Kong's population on subjects ranging from ethnic origins to mortgage payments. These questions will be conducted via a long form. The remaining 1.8 million households will be surveyed via a short form recording basic information such as age and sex. ''Statistics compiled from the information collected in the census are vital to government planning and policy formulation, particularly in such fields as education, housing, transport, medical and social services,'' Mr Ho said. ''The data is also important to the private sector in formulating business strategies,'' he added. On March 9 before the start of the census, letters will be sent to households, telling them whether they have to answer the short or long forms. Dr Ho said people did not need to worry about confidentiality. ''Information on individual persons or households collected in the census will be used for statistical purposes only. The Census and Statistics Department is legally prohibited from allowing access to this information by any government departments,'' Mr Ho said. He said completed questionnaires will be destroyed within one year after the Census. The survey is compulsory. Those refusing to co-operate will be subject to a $500 fine.