Most mobile devices nowadays have a camera. Besides, posting and sharing images have been found as one of the most frequent and engaging Internet activities. However, to our knowledge, no research has explored the feasibility of asking respondents of online surveys to upload images to answer survey questions. The main goal of this article is to investigate the viability of asking respondents of an online opt-in panel to upload during a mobile web survey: First, a photo taken in the moment, and second, an image already saved on their smartphone. In addition, we want to test to what extent the Google Vision application programming interface (API), which can label images into categories, produces similar tags than a human coder. Overall, results from a survey conducted among millennials in Spain and Mexico ( N = 1,614) show that more than half of the respondents uploaded an image. Of those, 77.3% and 83.4%, respectively, complied with what the question asked. Moreover, respectively, 52.4% and 65.0% of the images were similarly codified by the Google Vision API and the human coder. In addition, the API codified 1,818 images in less than 5 min, whereas the human coder spent nearly 35 hours to complete the same task.

Passive data from a tracking application (or “meter”) installed on participants’ devices to register the URLs visited have great potential for studying people’s online activities. However, given privacy concerns, obtaining cooperation installing a meter can be difficult and lead to selection bias. Therefore, in this article, we address three research questions: (1) To what extent are panelists willing to install a meter? (2) On which devices do they install the meter? (3) How do panelists who installed the meter differ from those who were invited but did not install it? Using data from online non-probability opt-in panels in nine countries, we found that the proportions of panelists installing the meter usually vary from 20% to 42%. Moreover, 20–25% of participants installed the meter on three or more devices. Finally, those who were invited but did not install the meter differ from those who did.

Millennials have been the focus of quite some research because of their differences with older cohorts. Besides, young respondents have been considered as a hard target population for surveys. However, to our knowledge, no research has compared the levels and types of survey participation of the Millennials versus the older generations. Using a dataset of 1,570,301 panelists of an opt-in online panel in eight countries from Europe, Latin America, and North America, we show that Millennials differ from older cohorts in terms of survey participation. Millennials show lower participation rates than older cohorts. Moreover, they present significantly higher proportions of surveys answered using smartphones. However, differences across cohorts in terms of break-offs and survey evaluation are mainly nonsignificant and/or nonmeaningful.

The increasing use of mobile devices in the frame of online surveys has been accompanied by the development of research apps. These research apps have the potential to facilitate the process for respondents (e.g. being able to complete surveys when Internet is not available provides more freedom on when and where participants can participate) and fieldwork companies (e.g. the possibility to use push notifications could lead to higher participation rates). However, previous research suggests that panelists may also be reluctant to install an app. In this study, we answer research questions related to the knowledge and use of the Netquest app. We found that a majority of panelist did not know about the app and although sending invitations significantly increased its installation, the overall total of respondents installing the app remained low. Furthermore, the profile of those who installed the app differs from those who did not. The participation of panelists after they installed the app seems stable. The main reason for installing the app is comfort while the main reason for not installing relates to space/battery usage. Most of those who did not install could accept to install the app.

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