How Fresh is the Field: An Initial Look

I run into a ton of really, really old studies and books while researching space habitation. For example, I found books on space habitation from my school's and my local library that look like they have not been opened since the Apollo program. All the articles I read seem to be from the 80's. This has built the impression in my mind that the field of space settlement is stale. However, before I make this claim, I have to prove it. This is my plan to prove of disprove my idea:

I want to look at every database I have access to and generate a list of every article I can field that is directly related to space settlement and articles where the author claims the paper be applied to space habitation. I also will include books on the field in the list. But, before I do that, I want to see if there is any value in doing this. So, I did a smaller version of the massive study I want to do. 

I went to Google Scholar and ran a search for "Space Settlement". Out of the 500 articles found, 161 seemed to be related to this field after reading the abstract. I looked at the date of publishing, not the date it was written. Now, I know this isn't a random sample, the term space settlement could be more popular in our politically correct age then in the past and Google may only find newer articles. But, if, despite all those reasons for the data set to be made of mostly articles that are older then 1989, I find that most articles are that old, then I have a very strong reason to think most of the articles on space settlement are old.

Here's what I found:

In math speak:
The average is 1997.75
The median is 2002
The first quartile is 1990
The third quartile is 2006.25

But, all in all, it looks like this study, if fully done, could prove that the space settlement field is expanding. One of the things I think that helped accelerate research into space settlement is the growing fields of astrosociology and space law; I ran into tons of those articles in those two fields and they were newer. It would be worth looking into how much those fields make up for the academic work on space habitation.

So, I turn it over to you, the readers. Did you see any errors in the way I put this together? Do you think it is worth doing?

Edit: Here's my data, I forgot it. I also feel like I should point out that this is very subjective.