In an example, a submission of a confidential data value of a first confidential data type is received from a first user with one or more attributes. A plurality of previously submitted confidential data values of a first confidential data type for a cohort matching the one or more attributes of the first user are retrieved. A plurality of percentiles for the confidential data values are calculated. Then, an interquartile range is calculated for a first and a second of the plurality of percentiles. A lower limit for the first confidential data type and the cohort is computed by taking a maximum of zero or the difference between the value for the first of the plurality of percentiles and a product of a preset alpha parameter and the interquartile range. Then it is determined if the confidential data value submitted by the user is lower than the lower limit.