Utilizing Mobile Random Digit Dialing (RDD) Sampling Frames for Population Surveys in low- and middle-income countries in Latin America

As with our previous article on RDD sampling in developing regions: Sub-Saharan Africa, there has been a notable rise in the adoption of mobile telephones, especially in developing countries. Specifically, Latin America has also experienced an increase in cell phone ownership among its populations and an overall decrease in landline ownership among households. As a result of this, mobile surveys are a dominant method for data collection, particularly utilizing mobile RDD.

Random-digit-dialing sampling – the act of generating random phone numbers and screening them for connectivity in order to provide survey fieldwork organizations represents a highly productive and representative sample methodology for a national telephone survey. This method is predominately used in low-to-middle-income countries where traditional sampling methods, such as Face-to-face may be difficult due to poor infrastructure, traveling to remote rural areas or security concerns and online surveys are not feasible due to low internet penetration.

In contrast to listed sampling, RDD phone numbers ensure that every potential owner of a mobile device can be sampled rather than a biased or incomplete list from operators which can lead to significant sampling coverage errors.

Mobile surveys offer a number of advantages over traditional survey methods. They are often quicker and cheaper to conduct, as they do not require the same level of logistical planning as traditional surveys. They also have the potential to reach a wider audience, particularly in rural areas where traditional surveys may be difficult to conduct.

However, there are also some challenges associated with mobile surveys in developing countries. One of the main challenges is ensuring that the sample is representative of the population being surveyed. This can be difficult when conducting a household survey, as not everyone has access to a fixed or mobile device.

To address this challenge, researchers can use stratified random sampling, which involves dividing the sample population into different groups and then selecting a sample from each group. For example, they could divide the telephone-owning sample population among the prefixes of the national mobile providers and stratify the sample by the proportions of their subscriber’s market share.

Another challenge is ensuring that the survey is conducted in a way that is culturally appropriate and sensitive to local customs. This may involve adapting survey questions to native and many indigenous languages to ensure that respondents understand the questions being asked.

Despite these challenges, mobile surveys using RDD sampling have the potential to provide valuable insights into a range of issues in developing countries. For example, they can be foremost used to collect data for international program development and evaluation efforts.

Considerations for using mobile phone surveys with RDD sampling approach:

There are key factors to take into consideration when choosing mobile phone surveying, be it in the form of: Computer Assisted Telephone Interviewing (CATI), Interactive Voice Response (IVR), and SMS: Two way, or Push-to-Web. Among the primary items to look over when surveying a Latin America (LATAM) country are:

1. Telephone coverage and frame size
2. Language preferences
3. Access to reliable networks
4. Cultural sensitivity

Telephone coverage and frame size

Key metrics for determining whether a telephone sample frame is sufficient for covering the population are the telephone frame size, subscriber counts (active frame), and the population size of the countries:

• Telephone frame size – the sum of all possible telephone number combinations that can be generated according to the nation’s numbering plan, telephone number length, and available dialing codes and prefixes.
• Subscriber count – represents the populations that can be reached via a telephone number device and/or SIM card.
• Population size – the total count of residents that live in the country.

From these key metrics, we can derive crucial information such as how wide the Active rate (count of subscriptions/telephone frame*100)

And the telephone penetration rate:

(count of subscriptions/population*100) – calculate the number of telephone subscriptions per 100 inhabitants.
Phone coverage is the count of all inhabitants that have access to at least one mobile device or SIM card.

eg. In Brazil’s case, the metrics are:

Population*: 214,326,223 (2021)
Mobile phone frame size**: 1,378,700,000
Subscriber count*: 219,660,524 (2021)

Active Rate: 16% of the frame is active – 16 of 100 random numbers are expected to be working numbers.
Penetration rate (per 100 inhabitants): 102% – indicated that inhabitants have access to more than one mobile number device and or sim card – hence they have a larger probability of being over-selected in a random sample. Doesnt have any indication of non-coverage.

*Source: World Bank, 2021

**Source: ITU Numbering Plan for Brazil

One limitation when we have a high penetration rate among subscribers when calculating these metrics is the over-coverage of respondents owning 2 or more cellphone numbers. This may cause duplication and/or overlapping responses. If individuals provide different phone numbers for each survey, it becomes challenging to identify and eliminate duplicate entries. Additionally, multiple phone numbers may indicate a higher level of technology adoption or socioeconomic status, leading to a potential bias in the sample towards individuals with greater access and resources.

Language preferences

Although Spanish is spoken by a majority of the whole population in the region, Latin America is home to many different languages and dialects. hence the language preferences and fluency of the target population represent a major consideration when conducting RDD surveys.

As for literacy rates, unlike in Sub-Saharan Africa, Latin American literacy rates don’t pose a problem for undertaking any text-based surveys via cell phones as the average literacy rate is 94.5% for adult populations and 82.8% for the elderly. Also, a noteworthy indicator is the that youth portion (aged 15-24) is the highest literate segment of the adult population, with a rate of 98.7%.*
Enabling a text-based interviewing approach utilizing a WhatsApp or SMS ‘Push-to-Mobile’ online survey are cost-effective and convenient method compared to live caller CATI interviews which typically involve a fieldwork facility, field staff, and equipment.
For the elderly populations that have a higher degree of illiteracy or are not as technologically adapted to smartphone usage, a traditional Live caller CATI interview is a staple approach.

Spanish may be the predominant language among all LATAM Countries (except Brazil) The presence of multiple official and unofficial indigenous languages and dialects may pose a problem in getting sufficient responses across the whole region. For example, in Bolivia, in addition to Spanish, there are 3 other officially recognized languages: Quechua, Aymara, and Guaraní. IVR and SMS modes enable respondents to re-route the questionnaire to the desired language at the start of the interview, an option for which CATI interviewing will require interviewers to know more than one language of the most frequently spoken languages. Otherwise, the language barrier would risk non-response from the sampled respondent. On the other hand, there is the case of all Spanish-speaking countries which all distinct dialects and pronunciations, such as the case of Chile, Ecuador, and Argentina. For which a native speaker is needed to capture verbal survey responses correctly.

*Source: Statista, 2020

Access to reliable networks

As with Sub-Saharan Africa, most of the countries in LATAM are considered low or middle-income countries with vast geographic spawns, and network coverage among mobile services is not equally distributed across the entire geography of the county. Contributing to the undercover among certain populations in remotely far areas.

While mobile phone usage is high in LATAM, access to reliable network connections may vary across regions. Something to consider is the potential challenges posed by poor network coverage when conducting phone interviews and planning accordingly.

Certain remote areas may be disconnected from network service or the current network may not be permanently stable and would result in regular disconnections or power outages. Increasing decreasing response rates and increasing the disconnected rate of the screened active RDD mobile sample.

GSMA Network Coverage Maps provides a good and up-to-date overview of the geographical span of each country by the provider. Allowing researchers to foresee any possible under-coverages in rural areas or wider regions, and potential overrepresentation among urban areas such as major cities, as in the case of Cuba’s single state-owned mobile provider (ETECSA) coverage.

Cultural sensitivity

Each country in LATAM has its own unique cultural nuances. Researchers must take into account cultural differences and adapt their interviewing approach accordingly to ensure participants feel comfortable and understood.

To tackle this local expert team of researchers should provide comprehensive training to interviewers who will be conducting RDD survey interviews in specific countries. This should include cultural sensitivity training, language proficiency assessments, and guidance on navigating potential challenges specific to the region.

The region also has diverse socioeconomic conditions, which may impact access to mobile phones and willingness to participate in phone interviews. Take into account these factors when designing your sampling strategy and interpreting the results.

Telephone phone coverage and survey topics:

Top 3 Countries with the Highest Cellphone Ownership in LATAM:

• Colombia: Colombia has a large population and a rapidly growing mobile market. With a high smartphone adoption rate and widespread availability of mobile networks, Colombia is likely to have one of the highest mobile phone penetration rates in Latin America, estimated at 95.2%
• Uruguay: Same as the previous entry, the country has a tech-savvy population, and mobile phones play a crucial role in their daily lives. With the availability of affordable smartphones and widespread access to mobile networks, Uruguay is expected to have a high mobile phone penetration rate of 94.8%.
• Costa Rica: Costa Rica is another country with a significant mobile phone penetration rate. The country has a large population and a strong demand for mobile connectivity. With the presence of major mobile operators and increasing smartphone usage, Costa Rica is also likely to be among the top countries in terms of mobile phone penetration. With a comfortable rate of 94%

Top 3 Countries with the Lowest Cellphone Ownerhsip in LATAM:

• Cuba: This country has one of the lowest mobile phone ownership rates in the Caribbean and the whole of LATAM. Despite advancements in technology, a significant portion (47%)of the population still does not have access to mobile phones.
• Bolivia: Another country in South America with poor mobile phone penetration (70%) in Bolivia. The country faces challenges such as limited network coverage, high costs of mobile services, and a lack of investment in telecommunications infrastructure.
• Nicaragua: The mobile phone ownership rate in this country is among the lowest in Central America. Factors such as affordability, lack of network coverage, and limited access to technology contribute to this low rate (80%).

Sample Solutions has provided sampling for all South and Central American and Caribbean countries for surveys that occupy strategic fields for the regions such as:

The report showcases mobile phone coverage on the individual level among all LATAM nations in the region.

In this section, we will outline the key facts and figures relevant to mobile sampling for all countries in LATAM as well as in which programs and evaluation studies our sampling efforts have been implemented.

Our sampling has over the years enabled studies to be conducted using phone interviewing and has played an integral role in study design development for multiple international survey efforts for various fields and by many international organizations and Think Tanks like Pew Research Center, World Bank, Gallup, and other United Nations Agencies, PAHO in fields such as:

• Public health: COVID-19 monitoring, measuring public health risk factors, disease monitoring, and eradication, food security and nutrition.
• Education: Monitoring the quality of education and access to resources.
• Economic development: Microfinancing, agriculture, and job opportunities.
• Infrastructure projects: Development planning for roads, electricity, and telecommunications.
• Rule of Law and Civil Rights: Corruption Monitoring, Migration, and Indigenous People’s and Women’s Rights.

Advantages and Disadvantages of sampling survey respondents Using RDD for phone survey research in LATAM

Advantages of Random Digit Dialing (RDD) sampling for mobile phone surveys

Among the biggest advantages of mobile RDD in the LATAM region, we list:

Increased Reach:

RDD mobile sampling allows researchers to reach a larger and more diverse population. With the widespread use of mobile phones in LATAM, this method provides an opportunity to include individuals who may not have access to traditional landline phones or internet connections.

Cost-effectiveness:

Conducting surveys through mobile devices can be more cost-effective compared to traditional methods. By eliminating the need for paper-based surveys or in-person interviews, the research team can save on printing costs and travel expenses.

Real-time Data Collection:

Mobile surveys can be conducted in real-time, enabling researchers to gather data quickly and efficiently. This is particularly advantageous when studying time-sensitive topics or capturing immediate responses from participants.

Disadvantages of Random Digit Dialing (RDD) sampling for mobile phone surveys

Disadvantages to take into consideration for cell phone surveys conducted via RDD and Mobile surveys in the LATAM region may include:

Sample Bias:

Although RDD mobile sampling offers a wider reach, it may still suffer from sample bias. Not everyone in the Latin American region owns a mobile phone, which could result in the underrepresentation of certain demographic groups. Researchers need to be aware of this limitation and carefully consider their target population.

Response Rates:

Obtaining high response rates can be challenging when conducting surveys through mobile devices. Participants may be less inclined to respond to phone calls or text messages from unknown numbers, leading to lower rates compared to other survey methods.

Technical Limitations:

Mobile surveys may face technical limitations such as compatibility issues with different devices and operating systems. Researchers must ensure that their surveys are optimized for mobile viewing and consider offering alternative survey modes for participants who may encounter technical difficulties.

Best Practices for RDD Mobile Sampling in LATAM:

Localization:

To ensure survey questions are culturally appropriate and relevant, researchers should consider localizing their surveys for the Latin American region. This includes using appropriate language and accounting for cultural nuances.

Incentives:

Offering incentives can help increase response rates in RDD mobile sampling. Pollsters can consider providing small rewards or entering participants into a prize draw to encourage participation.

Data Security:

Researchers must prioritize data security and ensure that participants’ personal information is protected. This includes obtaining informed consent, anonymizing data, and securely storing survey responses.

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In conclusion, RDD mobile sampling offers an innovative and efficient approach to survey research in the Latin American region. By leveraging the widespread use of mobile devices, research efforts can reach a larger and more diverse population. However, it is important to be mindful of the challenges associated with sample bias, response rates, and technical limitations. By following best practices and adapting surveys to the local context, RDD mobile sampling can be a valuable tool for collecting data in Latin America.

About Sample Solutions

Sample Solutions is a member of the World Association for Public Opinion Research(WAPOR), the organization has presented on numerous occasions related to this topic and provides Dual-frame and single-frame RDD sampling for 170+ countries, including all countries in Latin America for CATI, SMS, and interactive voice response survey (IVR) survey modes. If you have a research project that may require an RDD phone sampling approach for a specific country, we warmly welcome you to request our complimentary Sampling Methodology Whitepaper and country factsheet from our RDD Sample Coverage Page.

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