Background:
Data collection for the 45 and Up Study, a cohort of quarter of a million people age 45 years and over in NSW, had been undertaken via postal questionnaires since its inception in 2006. Access to the internet and the use of the electronic communications such as email is becoming increasingly common however less so with people aged 65 years and over. Although contact with study participants using such electronic methods has the potential to be more efficient and more cost-effective than traditional postal methods there were concerns that this may result in lower response rates. Although online data collection has been used in the general population for health and social surveys and for longitudinal studies there is little knowledge on how the mode impacts on response in elderly populations.

Methods:
As part of the 2015 routine follow-up 10,000 participants who had an email address were randomised to either receive their invitation and questionnaire using email and the internet or to receive their invitation and questionnaire via post. Email invitations included up to two email reminders and postal invitations included one reminder.

Results:
It was feasibility to invite a sample of 45 and Up Study participants to complete their follow-up questionnaire via the internet and to use a web-based questionnaire. The postal data are still being scanned and collated. However early results are showing that for those participants with email addresses, response rates between the online and postal questionnaires are similar. Analysis will include comparisons by age, sex, socio-demographics, the quality of survey completion, time to completion and cost.

Conclusion:
Email invitation and online data collection is possible for longitudinal studies on health and ageing, and is substantially less expensive than the postal equivalent. However only a third of the participants had provided email addresses and so the data collection will always need to be mixed mode.