The case study explores the use of mobile network operator (MNO) data to measure inbound and outbound travel in Slovenia. This initiative, a collaboration between the Statistical Office of the Republic of Slovenia (SURS) and the Bank of Slovenia, aims to enhance tourism statistics by providing timely and granular data. MNO data helps estimate the number of Slovenian travellers abroad and inbound visitors to Slovenia, categorising them as tourists, same-day visitors, half-day visitors, or transit passengers based on their mobile network connection duration. While the data offers advantages such as more timely information and higher granularity, it also has limitations, including potential overestimation or underestimation of tourist numbers and lack of socio-demographic details.
Using mobile network operator data to measure inbound and outbound travel in Slovenia
Abstract
Modern technology usage generates a huge amount of data that can be used to evaluate different social phenomena and trends. One such example is mobile network operator (MNO) data.
Obtaining mobile network operator (MNO) data is a joint initiative between the Statistical Office of the Republic of Slovenia (SURS) and Bank of Slovenia, with the methodology developed by Bank of Slovenia. Using MNO data, the number of Slovenian travellers who travelled abroad and inbound travellers who visited Slovenia whether for several days (tourists) or one day (same-day visitors) are estimated.
Bank of Slovenia is (as SURS and National Institute of Public Health) an authorised producer of national statistics. It is responsible for calculating the balance of payments and international trade in services and has used MNO data as an indirect source to calculate the import and export of travel in the balance of payments since 2005. With the adoption of Regulation EU 2015/2120 which brought the roam like at home principle into force, the methodology needed adaptation. Bank of Slovenia therefore developed the methodology that is now in use as an input to calculate the balance of payments. The methodology is based on the duration of connection to the mobile network.
For SURS, the main purpose of obtaining MNO data is to gain an additional data source to supplement surveys already conducted by SURS in the field of tourism statistics to evaluate tourist flows in Slovenia. These data could address user needs for more timely data, since they are published before data on tourism travels of domestic population as well as before data on foreign tourists and foreign travellers (surveys conducted every three years). For the reference years 2021, 2022 and 2023 SURS published monthly data for the whole year. During 2024, SURS began to publish monthly data on a quarterly basis.
The observation units are users of mobile telephony services abroad – inbound users roaming in the Slovenian mobile telephone networks and Slovenian users roaming in international networks. Due to data limitations, they are presented (aggregated) only for the whole territory of Slovenia.
The data are collected from all MNOs that provide public communication networks and/or public communication services in the Republic of Slovenia by the Agency for Communication Networks and Services of the Republic of Slovenia (AKOS). Excluded are only very small mobile operators that have negligible market shares of less than 0.5%. AKOS is an independent body that among others regulates and supervises the electronic communications market and conducts tasks related to notification and international relations, technical matters and numbering space for telecommunications. AKOS’ jurisdiction includes collecting data for statistical purposes. SURS receives the data based on the National Statistics Act and the Annual Programme of Statistical Surveys.
Mobile operators send AKOS data aggregated according to the methodology determined by Bank of Slovenia. AKOS combines received data from all mobile operators and forwards them to SURS once a month. SURS has been receiving the data free of charge since August 2020.
Bank of Slovenia developed the methodology to classify users roaming on mobile telephone networks into four groups relevant for tourism statistics. Based on the duration of the connection to the network over a two-day period, an individual user is classified into one of four categories each day: tourist, same-day visitor, half-day visitor or transit passenger. Due to its geographical position, Slovenia is a transit country, and transit passengers thus constitute an important share of tourism. The following definitions are used:
Users: individuals who use mobile telephony services while roaming on international networks. The user is defined by the phone number. Regardless of the number of roaming sessions in a given period (reporting month), an individual user is counted only once.
Slovenian users: subscribers and prepaid subscribers of Slovenian mobile phone operators who roam on international networks.
Foreign users: subscribers and prepaid subscribers of international mobile phone operators who roam on networks of Slovenian mobile phone operators.
Tourists: the total duration (despite possible interruptions) of the data exchange session over two consecutive days was between 18 hours and 48 hours.
Same-day visitors: the total duration (despite possible interruptions) of the data exchange session over two consecutive days was between 12 hours and 18 hours.
Half-day visitors: the total duration (despite possible interruptions) of the data exchange session over two consecutive days was between 6 hours and 12 hours.
Transit passengers: the total duration (despite possible interruptions) of the data exchange session over two consecutive days was up to 6 hours.
The data are published as experimental statistic on the number of users and visits (for tourists it is the duration of their stay in Slovenia) by the four above mentioned categories. The sum of users by type generally exceeds the total number of unique users, as an individual user can appear as several different types over a month.
Slovenia, December 2022, experimental statistics
Source: Statistical Office of the Republic of Slovenia
SURS receives aggregated data and not microdata, which means that the data cannot be used to conduct in-depth analyses. The data are subject to content review. In the case of divergent values, AKOS is notified and contacts mobile operators that investigate the issue and revise the data if necessary.
Advantages of MNO data
More timely data. The data are received on a monthly basis and published on a quarterly basis, two months after the reference quarter. The survey on inbound travellers on the other hand, which is used to estimate the share of same-day visitors, transit travellers, etc. and their expenditures is conducted every three years.
Higher data granularity. The data contains information on mobile phone users’ roaming for every single country from where the mobile phone users came to Slovenia or Slovenian users travelled abroad. Compared with survey data, MNO data provides information for a wider range of countries. For example, the survey on outbound tourism provides data that are sufficiently precise enough to be published for around 6-10 countries, while MNO data provides information for more than 100 different countries.
Analysing the impact of events on tourist flows. The MNO data was used to analyse the impact of COVID-19 on Slovenian tourists’ travel (for example, data showed an increase of trips Greece because Greece was one of the first countries that eased COVID-19 restrictions), and the data show the impact of certain events on tourism trips (for example, data showed an increase to Japan due to the Olympic games in Tokyo in July and August 2021). Likewise, impacts of events could be seen for inbound visitors (Russia’s war of aggression in Ukraine caused an increase in the number of Ukrainian visitors, and a decrease of Russian visitors).
Coverage. The MNO data covers inbound tourists that are not included in the monthly accommodation statistics (inbound tourists who stay at relatives and friends, or their own secondary homes).
Disadvantages of MNO data
Coverage. The MNO data on users can overestimate or underestimate the total number of tourists.
Potential overestimation of the number of tourists:
The MNO data include users that are not in Slovenia for tourism purposes such as truck drivers and daily commuters to work. Since only aggregated data are received, it is not possible to exclude mobile phone users who came to Slovenia for non-tourism purposes using only the MNO data. This would require combining the MNO data with alternative sources, for example data on inbound daily migrants from neighbouring countries or data on road cross-border traffic of passenger vehicles.
The data may also include the usage of other portable or smart devices. Internet of things and machine-to-machine devices can use mobile phone networks to exchange data. Mobile operators will try to adjust the algorithms to exclude such devices, however, this may not always be possible.
Mobile phone operators process only their own data. The potential double counting of users who roam on two different networks could result in overestimating the number of tourists. According to AKOS, inbound users of mobile phone services while roaming in Slovenia mostly use the services of bigger mobile operators that have good signal coverage so switching from one operator to another does not happen so often.
People that use more than one mobile phone can also result in double counting of tourist visitors.
Potential underestimation of the number of tourists:
The data includes only travellers with an active mobile device, which is not a requirement in the case of other surveys. To estimate the share of travellers that do not bring a mobile phone or are not using their mobile phone while in Slovenia, SURS included additional questions to the Foreign Tourists and Foreign Travellers surveys. The questions were on the number of people in the travel party that brough a mobile phone, and for what purposes the mobile phones are used (for example, making a phone call, sending or receiving a text message, data transfer over a mobile network, data transfer over a wireless network).
Aggregated data. The data are aggregated, which means that detailed analysis of microdata is not possible.
Country of residence. The country of issuer of the SIM card is assumed to the country of residence of the tourist. With the appearance of eSIM cards, data on the country of residence may be incorrect. The eSIM cards can be easily purchased online by customers from all around the world, and with the card they can roam in every EU member state without paying additional charges. The users of eSIM cards, offered by mobile phone operators in the EU, are added to the country of the mobile operator that provides this service, and not the actual country of residence.
No additional information. The MNO data does not contain any additional information about the mobile phone users, such as socio-demographic characteristics, purpose of visit, or their expenditure. Surveys are still needed to obtain this information.
Not used for absolute estimates. Given the current methodology and challenges, the MNO data are not completely suitable for absolute estimates. As such, the data are used to monitor tourist flows in a relative way (increase or decrease of individual groups).
Data users always have the needs for timely and granular data. This was accelerated by the pandemic and the digitalisation of society and the economy. With the published MNO data, the main stakeholders within tourism can or will be able to monitor tourist flows more frequently and at more detailed level in regard to the country of origin of the inbound mobile phone users in Slovenia, and for every country that Slovenian mobile users travel to.
SURS publishes the data they receive from AKOS as news releases. The data are published as experimental statistics since the data are new and because the measuring instrument, the methodology of data collection and the indicators are still being developed and do not meet the criteria of official statistics. Data are disseminated according to the SURS’ dissemination and communication policy. Additionally, detailed data are published in the SiStat Database.
The collaboration with AKOS and Bank of Slovenia helped set up this experimental statistic. Because the field of telecommunications develops quickly, the biggest challenge for SURS is how to recognise, capture and adequately interpret all the changes in the set-up and methodology. Users are informed about methodological issues that are important for interpreting the data in a methodological note (under the press release and in the methodological explanations).
A challenge has been receiving the data from the MNOs so that there is enough time for AKOS and SURS to perform basic checks, identify inconsistencies and to request MNOs to correct and resubmit the data if relevant. Following the provisions of GDPR, MNOs can only store the individual data for three months, after which they have to delete all individual data and additional corrections are no longer possible.
Although the use of MNO data for tourism purposes is still a relatively new and experimental statistic and has not yet reached a wide range of users, the main stakeholders in the tourism sector have provided positive feedback on the data. With the continuous publication of the data, the range of users is expected to broaden.
Due to differences in methodologies, coverage, and the challenges mentioned above, statistics from MNO data are not completely comparable with statistics obtained from traditional surveys. Although the MNO data cannot replace traditional surveys, they provide relevant insights in the tourist flow trends.
For further information please contact:
Nataša Sabljić, Undersecretary, Statistical Office of the Republic of Slovenia, Natasa.Sabljic@gov.si
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