Collecting Same Data Four Months Later

On Oct. 7, 2006, I requested HRD Crew members to respond to the following two questions:
1. What experience(s) have you had in using pod technology?
2. What are your barriers to using pod technology?

After sharing the data analysis with the Crew and waiting four months, I asked the same two questions to the HRD Crew.

The similarities of the two surveys are:
1. Same two questions
2. Same group of participants, HRD Crew. Although a few members may have left HRD since Oct. 6, 2006 and a few members may have been hired after Oct. 6, 2006, all members are encouraged to respond.
3. Request was sent by email
4. The request to reply was a one work week, Mon. through Fri.

The differences between the Oct. 7, 2006 survey and Feb. 12, 2007 survey procedures are:
1. The word "all" was added to the email greeting. If I spoke to a clerical staff member, I mentioned the email request.
2. The time is four months later
3. The February replies are in reference to their experiences after Oct. 7, 2006

I wanted to ask the question, What contributed to the change, if any, from Oct., ? However, to be consistent, I only asked the same two questions.

There is the possibility that I could consider asking particular respondents further question(s) based on their responses. I will wait at this time to ask other questions.

I believe this is a longitudinal study and will do some research on that topic.