He's just completed a survey of more than 13,000 voters in 41 of the most marginal seats in the country *. (conservativehome.blogs.com)
You could earn miles and points for completing surveys and these rewards can be redeemed for airline and hotel rewards. (theglobetrottingteacher.com)
We explored whether participants who had invalid email addresses were different from those who had valid addresses and we compared those who completed the survey with those who did not. (link.springer.com)