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Data Suppression: An explanation

We are aware that some data which users want to upload into Local Insight may be very sensitive. Therefore we have measures in place to protect this data.

  • The raw data that is originally uploaded into Local Insight is deleted once it has been aggregated. 
  • Suppression can be applied to help ensure that sensitive data is not stored on Local Insight. When uploading metadata, you are given the option to apply suppression at a specific value:

How does suppression work?

The suppression threshold is the minimum number of data records that an area must have for suppression not to occur. For example, if a user sets a suppression threshold of 2, then standard or custom areas with at least 2 data records will show the actual aggregated value of data points, whereas standard and custom areas with 1 data record will show a suppressed aggregate value.

  • Data records refer to each individual cell on the import. For example, the highlighted line below is 1 data record

 

Local Insight records the average data value for every upload. This average is then used for suppressed data. The way the data is suppressed depends upon the aggregation type - whether users have chosen the 'sum' or 'average' mechanism - so you will likely see different results when uploading the same data using different methods. Where data has been suppressed for an area, the map and the 'data for your areas' show the average value for that whole upload, aggregated to that specific area.

Example of suppression in practice:

  • Imagine uploading a dataset called 'number of smokers', using the aggregation type 'sum' and setting a suppression-threshold of 3
  • A custom area with only 2 data values (postcodes) for this area would, therefore, be suppressed
  • Data for this area would show the average for the upload - which for a ‘sum’ variable would be the number of data points (in this case 2) multiplied by the average value of the upload (let's say 4 smokers per postcode) to give the average value of 8
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