A probability-based mixed-mode approach for RDD Sample in Germany

The probability-based mixed-mode approach enhances participant selection by ensuring each person in the target population has a chance of being chosen for the survey. It combines various data collection methods to improve response rates, data quality, and representativeness. In this article, we investigate how this approach is gaining popularity in Germany as it overcomes the limitations of traditional phone surveys through the use of multiple modes such as telephone interviews, SMS surveys, and mail questionnaires. Overall, the probability-based mixed-mode approach improves sample representativeness and provides a comprehensive understanding of the population being studied.

How probability-based mixed-mode surveys can be implemented?

In a mixed-mode approach, the distribution of data collection modes can be tailored based on the characteristics of the target population and research objectives. To ensure comprehensive coverage and account for the non-internet population, it is possible to allocate a larger proportion of the sample to online surveys while incorporating other modes, such as telephone interviews, to capture respondents who do not have internet access or prefer alternative modes of participation.

Most commonly, the mixed-mode approach combines telephone and online data collection. You could be collecting data via online and phone at the same time in order to achieve consistently high response rates.. Here is a more detailed outline of how a mixed-mode approach would be implemented:

Probability-based Sampling

Begin by conducting a random selection of households or individuals from the target population using probability-based sampling techniques like random digit dialing (RDD. This step forms the foundation of the mixed-mode approach, ensuring the sample is representative.

Probability-based mixed-mode panel

Probability-based mixed-mode panel refers to a research methodology that combines multiple modes of data collection (such as online surveys, telephone interviews, face-to-face interviews, etc.) in a panel study, where participants are selected based on probability sampling methods.

Participation in a probability-based panel

The panel members are then invited to participate in various surveys or interviews through different modes of data collection, depending on their preferences or the requirements of the study.

Overall, probability-based mixed-mode panels offer a flexible and efficient approach to collecting data by combining different modes of data collection while maintaining the rigor of probability sampling.

Online web surveys (85%)

To realise this aim in a cost-efficient way, a first mode is often an online questionnaire, towards which the target persons are pushed. The majority of the panel sample is conducted through online surveys, leveraging the advantages of cost-effectiveness, efficiency, and scalability. Online surveys can be distributed via email invitations, panel member portals, or online survey platforms. This mode is particularly suitable for participants who have full access to the internet and are comfortable with online data collection.

Telephone Interviews (15%)

To ensure representation of the people who do not use the internet and reach individuals who may have limited internet access, a portion of the sample is allocated to telephone interviews as a second mode. This mode allows for direct communication with respondents and can be conducted using landline or mobile phones. Telephone interviews can be especially useful for targeting specific demographics, such as older adults or individuals residing in areas with lower internet penetration.

Advantages of using the Probability-Based Mixed-Mode Approach:

Applying a mixed-mode approach for surveys offers several advantages and can help overcome various challenges associated with data collection. This approach allows for flexibility, allows researchers to collect better data quality, helps in terms of response rates, allows respondents to choose the participation mode, allows the respondents the participation in a probability-based panel, and provides a comprehensive understanding of the target population while adhering to the principles of probability sampling.

Using a mixed-mode approach can enhance survey quality in several ways. Here are some of the benefits of a mixed-mode survey:

Reducing nonresponse in a probability-based panel study 

Mixed-Mode surveys increase survey participation. Incorporating alternative modes, such as online surveys or mail questionnaires, provides respondents with more flexible options. Individuals who are reluctant to participate in telephone interviews may prefer these alternative modes, resulting in higher response rates and reduced nonresponse bias.

Maximizing Data Quality with different effects of modes

If you find yourself grappling with concerns about the quality of your survey data, adopting a mixed-mode survey may hold the key to resolving them. Mixed-mode surveys offer a compelling solution to address data quality concerns effectively and ensure more reliable and valid results. Different modes may influence respondents‘ answers, resulting in mode effects. For example, sensitive or personal questions might be better suited for online surveys to encourage more candid responses. This flexibility in mode selection contributes to improved data quality and enhances the richness of the collected information. Each mode has its strengths and weaknesses, and employing a mixed-mode approach allows researchers to leverage the advantages of each mode to optimize data quality and to compensate for their weaknesses.

Cost-Effectiveness of online panel research and offline modes

Mixed-mode surveys may offer positive effect on overall survey costs and time efficiencies. For example, online surveys can be more cost-effective compared to face-to-face interviews, as they eliminate the need for interviewer travel and can reach a larger audience. By strategically combining modes, researchers can optimize resource allocation while maintaining data quality.

Longitudinal Surveys

Mixed-mode approaches are particularly valuable for longitudinal studies, where data is collected from the same individuals for multi-wave panel study over time. Using a single mode throughout the study may lead to panel attrition or decreased respondent engagement. The idea of a sequential mixed-mode strategy does work even in the case of competing risks in the choice of a survey mode. By offering multiple modes, researchers can maintain panel participation and gather data from individuals who may prefer different modes at different points in time.

Access to a wider demographic range

The digital aspect of the mixed-mode approach allows for greater accessibility to various demographic groups, including younger individuals who may be less likely to participate in telephone surveys.

Applications of the probability-based mixed-mode surveys in Germany 

Recognizing the changing landscape of communication and the need to adapt to technological advancements, Germany embraced the concept of mixed-mode data collection like the GESIS Panel uses it for multiple panel waves. This approach combines RDD sampling with online surveys, providing researchers with an opportunity to tap into a wider range of participants while maintaining the representative nature of the sample.

Germany, like many other countries, has experienced a decline in response rates to traditional survey methods, such as face-to-face or telephone interviews. By offering respondents multiple survey modes of participation and the choice of a survey mode, such as web-based surveys or mail surveys, researchers in Germany can increase the chances of engagement and improve overall response rates for their web survey. Individuals who may be less inclined to participate in one mode may find another mode more convenient or preferable, leading to enhanced participation and reduced non-response bias.

Germany has a diverse population with varying preferences for communication modes. Some individuals may prefer online platforms and mobile devices, while others may still rely on traditional telephones or face-to-face interactions. By incorporating different modes, researchers can cater to these preferences and ensure that a broader range of individuals are included in the survey sample using a push-to-web approach. This approach helps maintain the representativeness of the sample and reduces potential biases associated with relying on a single mode.

The probability-based mixed mode approach holds great potential for enhancing RDD sampling in Germany across various domains. Researchers can employ this approach to conduct public opinion polls, social science research, market studies, and even longitudinal data more.

A probability based mixed-mode approach for CATI centers

A probability-based mixed-mode approach for Computer-Assisted Telephone Interviewing (CATI) centers involves combining telephone interviews with other data collection methods, such as online surveys or face-to-face interviews. Mixed-mode surveys aim to leverage the strengths of various modes, creating a comprehensive approach that combines the advantages of different modes. The goal is to improve response rates and representativeness by offering respondents multiple options to participate in the survey.

Here are some key considerations for implementing a probability-based mixed-mode approach in CATI centers:

Sampling: Start with a probability-based sampling frame that includes telephone numbers for potential respondents. Ensure that the sample is representative of the general population.

Telephone Interviews (CATI): Begin the data collection with telephone survey as the initial mode process with traditional telephone interviews conducted by trained interviewers. This approach allows for standardized data collection and minimizes nonresponse biases commonly associated with other modes.

Recruitment and Incentives: Encourage respondents to participate in the survey by explaining the purpose and benefits of the study. Offer appropriate incentives, such as cash rewards or gift cards, to increase participation rates.

Follow-Up Strategies: Implement effective follow-up strategies to minimize nonresponse rates. This may involve multiple call attempts at different times of the day or week, using different interviewers, and employing persuasive methodological techniques to engage potential respondents. This feature of survey management is effective in countering panellists’ procrastination in regard to responding to a survey. The use of reminders might be useful in solving this problem of competing risks. It is confirmed that reminders increase the response rate.

Online Surveys: Provide respondents with the option to complete the survey online as a subsequent mode. This allows participants who prefer or are more comfortable with online surveys to contribute their responses.

Data Integration: Merge data collected through telephone interviews and online surveys to create a unified dataset.


Implementing a probability-based mixed-mode approach offers a comprehensive sampling strategy to ensure representativeness and coverage of diverse demographics. By combining online surveys and telephone interviews, researchers can capture insights from both internet and non-internet populations, obtaining more robust and inclusive data.

In summary, the probability-based mixed mode approach serves as an effective strategy to overcome challenges in survey research, including declining response rates, mode preferences, accessibility issues and mode effects. By combining multiple modes, researchers can enhance response rates, reach diverse populations, ensure representation, and improve the overall quality of survey data.

The mixed-mode surveys appear to offer opportunities for broader reach and increased participation, leading to more representative and reliable survey results.

About Lifepanel – Probability-based Online Panel

With over a decade of experience in sampling and CATI Data Collection, Lifepanel – a probability-based online panel research is founded in 2022.
We designed a probabilistic panel, based on a representative, dual-frame RDD sample.
Membership to our panel is by invitation only, we use the RDD telephone sample to invite the respondents to join Lifepanel. All panel members are phone verified and randomly selected.
Panelists are recruited from landline and mobile telephone frames. With close to full coverage in most European countries, coverage bias is significantly reduced. Respondents without internet are re-contacted via phone. The recruitment is done via CATI, SMS and Whatsapp.

Lifepanel Demographics
Lifepanel uses a variety of key demographics such as: Age, Gender, Household size, Level of Education, Current Employment Status.

Medina Zhaku
Medina Zhaku