"Expression of Interest" rate reflects what percentage of her mail the lady returns. It does not, however, show if the lady answered positively or negatively to the "Expressions of Interest". Most women seek a special person, not just anybody, so they are very selective. If a lady's response rate is 100%, it only means she returned all enquiries she received, i.e. this lady answers her mail. If a lady's response rate is 0%, it means she does not check her mails or have not had a chance to check them yet.

For example, if a lady received 10 "Expressions of Interest" and answered 4 of them (either positively or negatively), her response rate will be 40%. 

Usually "Expression of Interest" rate will be lower for new ladies because they have just started their search, and if she received 5 enquiries yesterday and returned them, and she received 5 new enquiries today and have not returned them yet, her response rate will be only 50%. For the ladies that are longer on the website, if she received 95 enquiries before and returned them, and she received 5 new enquiries today, her response rate will be 95%.