Practical Considerations The following section examines the conditions which would make CDR data useful for tracking mobility. The main consideration is whether CDR would capture representative data on the mobility of the entire population of interest. This is influenced by both mobile phone use patterns and mobile phone infrastructure. Use patterns
CDR data tracks SIM cards, not individual people. None of the case studies have universal or uniform cell phone use, in other words, where every individual has a single SIM card, carries it constantly, and uses it regularly. Rather, many contexts feature families sharing one SIM card or one individual owning and using multiple SIM cards. These differences in use and ownership patterns suggest that while CDR reflects the movements of SIM cards, this may not provide a complete picture of the movements of individuals or populations. Additional issues concerning how CDR does not track individual persons are examined throughout this section.
Skewed cell phone access or use among population subgroups can lead to biased representation in CDR data. Cell phone ownership is typically less common among more vulnerable populations, including women17 and children, the poor, and the elderly.18 In some contexts, when SIM cards are shared by families, cell phone use is often controlled by the head of household, making cell phone use less accessible to women and children.19 In addition, marginalized populations are at times systematically excluded from cellular communication systems and would therefore be missing from CDR data. SIM card purchasing requirements affect who has access to cell phones and who is left out. MNOs in some countries, such as El Salvador, require individuals to show formal identification to obtain a SIM card.This requirement creates barriers for certain subgroups to own and use cell phones. Using CDR in these contexts presents the risk that only data from connected groups would be analyzed. Similarly,
Figure 3: Use patterns affecting CDR data
Multiple SIM cards for a single user
Multiple users with same SIM card
The potential value of CDR is highest when cell phone use for phone calls and SMS messages is common across the population of interest. In this report’s ten case studies, rates of cell phone penetration (measured as number of mobile subscriptions per 100 inhabitants) ranged from 22 in Micronesia to 155 in the Philippines. Penetration rates over 100 indicate that individuals often hold more than one mobile subscription, often with different MNOs. In countries like Micronesia, where cell phone penetration is particularly low, CDR may not provide representative information about overall population movements.
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Inconsistent and irregular usage
Pre-paid phone plans
the Rohingya refugee community in Bangladesh is systematically denied cell phone access because a national ID is required to purchase a SIM card.20 Instead, they have few options but to buy SIM cards informally from Bangladeshis, usually at significantly inflated prices and with the risk of subjection to regular government crackdowns.21 Reliance on prepaid plans can also limit CDR’s accuracy. When most mobile users in a country subscribe to prepaid rather than monthly plans, CDR may become less reliable in the immediate aftermath of a natural disaster. After the 2010 earthquake in
Assessing the Use of CDR for Monitoring Mobility and Displacement
