While CDR data has an important role to play in the response to COVID-19, it is important that considerations are made to the suitability of its use. This includes a range of technical and social reasons as described below.
Potential for misuse of mobility indicators
There are rightfully concerns about the potential for misuse of mobility indicators derived from CDR data. We recommend that indicators are be provided in real-time but with a delay of at least a day. This delay would prevent its use to identify ongoing gatherings and to be used as a policing tool. Splitting up individual gatherings rather than focusing on structural causes of gatherings and the employment of effective communication and mitigating causes of gathering, is unlikely to make a relevant difference to transmission of SARS-COV-2. They do however serve to increase the risk of violence and may set a precedents for inappropriate surveillance. In addition, it is worth noting that indications of changes in mobility are not a measure of the number of people who do or do not comply with mobility restrictions. Restrictions have a number of exemptions which cannot be quantified using CDR data alone. Exemptions include, for example, key workers (e.g. health sector, law enforcement, military, maintenance of essential service, supply chain of essential products, etc..), people returning home, people supporting their families, people in need of health care, etc... Therefore, as we cannot quantify exemptions, we cannot quantify compliance.
Importance of the country context
Secondly, as the indicators are designed to be exhaustive and capture all dimensions of mobility to inform a range of possible questions, the usefulness of each and every indicator will depend heavily on the country context. This not only includes the needs of the country, but factors influencing the availability and representativity of the data (coverage, density of towers, frequency of phone usage).
Representativeness of CDR data
Finally, CDR data from a mobile network operator only contains information about the people who use a SIM card from that operator. This subset of people is unlikely to be perfectly representative of the entire population of a country because not everyone uses a mobile phone, and not all mobile phone users are subscribed to a single mobile network operator. For example, young children and elderly people in many countries do not use a mobile phone, and in low-income countries, individuals in the lowest socioeconomic strata may not own a mobile phone. Additionally, the geographic, demographic, and socioeconomic distribution of subscribers to each mobile network operator is often not representative of the behaviour of the entire population.