The mandatory American Community Survey (ACS) takes 40 minutes to complete on average and i s often answered using the ACS online instrument on a desktop or laptop computer. However, recent analysis has indicated that there is a small but growing segment of respondents who answer the ACS using their mobile devices (Horwitz, 2015). While the current ACS instrument can be completed using a mobile device, at the time of this study, it had not been optimized for viewing on a small screen. While ACS had plans in development to make the screens more mobile friendly, the team wanted to test it prior to the mobile optimization changes in order to have a baseline to compare the optimized version against. Given these developments, members of the Center for Survey Measurement (CSM) and the Decennial Statistical Studies Division (DSSD) collaborated to investigate how respondents interact with the ACS online instrument, prior to the screens being optimized for a smartphone or tablet. The goal of the usability evaluation was to identify how the online ACS performed for respondents who answered while using their own mobile device (e.g., smartphone or tablet) as well as to identify screens which were more challenging to complete on a mobile device. Usability findings indicated that for most small devices, it was very difficult to complete the survey without a lot of extra manipulation, such as zooming in to read the survey question and response options. This was time consuming and frustrating to the user. Recommendations for improvement are to optimize the ACS for mobile devices. This includes implementing design changes that were already made for the Decennial 2015 census online questionnaire, based on a style guide created by an inter-departmental Census Team (see Nichols et al., 2015). The guide suggests:

• Reduce the use of white space and increase the font size so that the screen is filled primarily with just the question and the response options
• Allow more space between response options
• Reduce the amount of text on the screen, (e.g., login page, instructional texts, etc.)
• Minimize the size of the banner

Not in the guide, but for ACS specifically, we recommend removing the right-hand navigation menu.