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Disclosure control and small area statistics. Grids or blobs? With comparison of two small areas. Vilni Verner Holst Bloch Cand.scient. landscape ecology and natural resources Statistics Norway Otervegen 23 N - 2225 Kongsvinger Tel : ++47 / 62 88 50 62 Fax : ++47 / 62 88 54 59
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Disclosure control and small area statistics Grids or blobs? With comparison of two small areas Vilni Verner Holst Bloch Cand.scient. landscape ecology and natural resources Statistics Norway Otervegen 23 N - 2225 Kongsvinger Tel : ++47 / 62 88 50 62 Fax : ++47 / 62 88 54 59 E-mail : vvh@ssb.no
Increasing demand for disclosure control Even smaller area statistics - easier to identify/recognice persons or communities More detailed statistics – more sensitive data More available statistics – easier to combine and derive other information (classic ex.: elder single person with lots of money)
Disclosure depend on geography (radius 75 m) Addresses Oslo municipality – 66 000 addresses (coordinate pairs) Persons
Disclosure varies with time and society Norwegian population cencus 1910 - about amongst others; returned norwegian-americans, dissidents, blind people, deaf people and lunitics
Advantages of grid Stable land units makes measuring change in geographical concentration easier (?) Measuring co-variation when lacking exact geographical match Easy data handling – do not need GIS
Advantages of blobs High geographical accuracy Easy to read – less ”noise” in the map
A comparison Stovner Central Oslo
Information on address level Stovner Central Oslo
Residents per 100 x 100 m gridcell Stovner Central Oslo
Employees per 100 x 100 m gridcell Stovner Central Oslo
Education in neighbourhood Stovner Central Oslo
Disclosure rules in Statistics Norway Blobs Statistics based on this method – given criterias of radius minimum 75 m, minimum 10 livingaddreses and 10 units – may be published. Grids Standard criterias for disclosure control yet to be decided. In practice minimum classes has been 1-4 residents or 1-19 employees.