Finding scientific papers for free, part II: comparing methods

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Sandra Porter

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This is the second part in a three part series on finding free scientific papers. You can read the first part here: Part I: A day in the life of an English physician

Today, we do an experiment with PubMed and PubMed Central to determine the best way to search for free articles.

The biggest problem that our doctor friend, from part I, faced, wasn't that he couldn't find the information he wanted. His problem was that he found too much information. And, most of what he found, he couldn't get at. He wasn't happy about following several links only to find that he couldn't read the articles.

I thought that he might be happier and certainly save some time by limiting his search to the articles that are free and skip the others. The problem is that there are a few different ways to do this. So, I decided to compare them and determine which method would give the largest number of free articles, and the most recent publication dates.

Here is the method to my madness: I searched either PubMed or PubMed Central through the National Center for Biotechnology Information (NCBI) with the term "cancer." Then, I either limited the search (using Limits, shown as "PubMed Limits" in my graphs below) or I used the Display menu to filter the results (shown as "PubMed PMC" links in the table). Last, I sorted the results by date to see which search method gave the newest publications.

The results:
It's not surprising that our physician friend from the National Health Service was frustrated when he searched PubMed and then tried to look at the articles. In my experiment, only 11 percent of the articles that I found were freely available, and that was when I used the best method.

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So what does this all mean?

The first column shows all the cancer citations that I found with PubMed. The next three columns show the results from three methods I use for finding free articles. The least successful method was to use the PMC links filter. When I took my PubMed results and filtered by PMC (PubMed Central) Links, I only found a fraction of the articles that were really available, and the most recent article was from April 28, 2007. This is because filtering is limited to the first 10,000 items for this database.

If I searched PubMed Central directly, I obtained more articles, but the most recent articles were from May. My PubMed search, on the other hand, had located articles, from June. (Yes, June hasn't happened yet, but some articles can be found before they're officially published.).

Overall, I found the best method, with the most results, was to use PubMed and limit the articles to those with free full text. While it's certainly true that 219,985 articles are way too many for me to read, at least I know I'm getting the most recent articles, and that I will be able to view the articles that I choose to investigate.

Plus, one of the tabs limits the results to review articles. (Review articles, for those who don't already know this, summarize the results of other articles.) With 14,819 reviews, I can limit the search criteria even more, have a much better chance of finding what I want and I don't have to waste my time trying to look at articles that I can't access.

Read the whole series:

  • part I A day in the life of an English physician,
  • part II Comparing different methods,
  • part III My new favorite method,
  • part IV One last experiment