Data pseudonymisation

On this page: pseudonymous, de-identification, replacement, open science, reuse
Date of last review: 2023-03-30

YOUth (Youth of Utrecht) is a longitudinal child cohort study that collects data about the behavioural and cognitive development of children in the Utrecht area. The study follows about 4000 children and their parents in two cohorts. One from birth until around the age of six, one from around 9-years-old until adolescence. YOUth collects a wide variety of data types, ranging from questionnaires to biological samples. Because of the large amount of data and the sensitive nature of the data and the participants (minors), the data can be considered as very sensitive, and thus should be pseudonymised where possible.

General steps

YOUth is committed to sharing their data for reuse, and thus the datasets that they share should contain as little personal information as possible. For that purpose, the YOUth data manager implements a number of measures:

  • All data are pseudonymised as much as possible (see below).
  • Every dataset that is shared for reuse is first checked for identifiable information. Special category information is taken out of the datasets as much as possible, and no unnecessary information such as date of birth is shared.
  • Using the tool AnonymoUUs, participant pseudonyms are replaced with artificial pseudonyms, and all dates with a fake date, each time a new set of data is prepared for sharing. This limits the ability of external researchers to link multiple requested datasets together and thus to form a more complete image of each participant. It also prevents singling out participants based on the day they visited the research centre.

Pseudonymisation per data type

Below is an overview of the data types and pseudonymisation measures taken by the YOUth data manager. Besides these pseudonymisation measures, YOUth has implemented a data request procedure which delineates the conditions under which researchers can access the data, and the steps they have to take to request access.

Questionnaire data (tabular)

Children and their parents/caretakers (sometimes their teacher) fill out several questionnaires about, among others, their mental and physical development, living conditions, and social environment.

Pseudonymisation measures:
  • A script removes unnecessary (special category) personal data from the shared dataset where possible, such as religion, ethnicity and open text responses.
  • If a researcher needs demographic information only to describe the sample, the data manager shares a frequency table of the requested information, for example for ethnicity and socio-economic status, instead of sharing the raw responses.
  • The Anonymouus tool replaces the pseudonym and date in the questionnaire data and file names.

In the future, the data manager would like to share only scale scores, instead of responses to individual questions in standardised questionnaires.

Computer tasks (tabular)
On a computer, children play various games to measure cognitive and motoric development of the child. In most games, the response times, choices and scores are recorded. To pseudonymise the data, the AnonymoUUs tool replaces the pseudonym and dates in the task data and filenames and in some cases even the name of the participant.
Logbook- and experiment book data (tabular)
Notes about data collection (data quality, task-order, if experiment started etc.) are made in logbooks by means of a data capturing tool. In that same tool, YOUth also collects research data about body measures (length, weight and head circumference) and intelligence (WISC and WPPSI) To pseudonymise those data, the AnonymoUUs tool replaces the pseudonym and date in the filenames and data.
Video tasks (video recording)

During two tasks (the Hand game and the Delay of gratification task), children are video- and audiotaped to be able to analyse their behaviour. Parents may also be visible in the background, as well as a research assistant.

To pseudonymise these data, both the videos from the Hand game and the Delayed gratification task will be coded/scored on the variables of interest (e.g., does the child take the candy out of the bag or not). This way, no actual video recordings will need to be shared with other researchers.

Parent-child interaction (video recording)
Children and their parents are videotaped while they play with each other or discuss specific topics. Because these data are difficult to pseudonymise and could be scored/coded on many different aspects, YOUth provides a special local laboratory space to perform the desired qualitative analysis on these video data.
Magnetic Resonance Imaging (MRI) data (3D image)

MRI data of children are collected to study structural (3D image of the brain, skull, and outer layers of the head) and functional (brain activity) properties of the brain.

To pseudonymise the MRI data, structural MRI scans (DICOM) are defaced using mri_deface (v1.22), resulting in NIfTi files. Additionally, the AnonymoUUs tool replaces the pseudonym in the filenames.

Electro-encephalography (EEG) data (video and text files)
A cap is placed on the child’s head with electrodes attached to measure brain activity. The child is placed in front of a monitor and views various on-screen stimuli (incl. faces, objects, sounds, music, toys). A video is also made to check whether the child watches the screen. For the moment, the videos will not be shared with external researchers. In the EEG data itself, the AnonymoUUs tool replaces the pseudonym and date.
Eye tracking data (text files)
Children are placed in front of a screen and view various stimuli (incl.  faces, objects, sounds, music, toys), with or without an assignment. Eye movements and focus points are recorded using an eyetracker. To pseudonymise these data, the AnonymoUUs tool replaces the pseudonym and date in the eyetracking data and the filenames.
Ultrasound images (3D echos)
During the mothers’ pregnancy, 3D ultrasound images are made of foetuses to follow overall and brain size development. To pseudonymise these data, the ultrasound images (DICOM) will be converted to nifti (.nii) format, which does not contain header information. Additionally, the AnonymoUUs tool replaces the pseudonym and date in the filenames and in the SQL database that comes with the measurement.
Biological materials
At various moments during the study, (chord) blood, hair, saliva, and buccal swabs are taken from the child and sometimes their parent(s). The samples cannot be pseudonymised, because they are physical samples. Instead, a procedure is in place to have biological samples analysed at preferred partners, without having to share the physical samples with researchers.