Re: Manual Evaluation of Algorithm Performance on Identifying OA

From: Stevan Harnad <>
Date: Tue, 28 Mar 2006 00:47:21 +0100

    Previous AmSci Topic Thread:
    "Manual Evaluation of Algorithm Performance on Identifying OA"
    (Dec 2005)

    Antelman, K., Bakkalbasi, N., Goodman, D., Hajjem, C. and
    Harnad, S. (2005) Evaluation of Algorithm Performance on Identifying
    OA. Technical Report, North Carolina State University Libraries,
    North Carolina State University.

    Hajjem, C., Harnad, S. and Gingras, Y. (2005) Ten-Year
    Cross-Disciplinary Comparison of the Growth of Open Access and How
    it Increases Research Citation Impact. IEEE Data Engineering Bulletin
    28(4) pp. 39-47.

In an unpublished study, Antelman et al. (2005) hand-tested the
accuracy of the algorithm that Hajjem et al.'s (2005) software robot
used to identify Open Access (OA) and Non-Open-Access (NOA) articles in the
ISI database. Antelman et al. found much lower accuracy (d' 0.98, bias
0.78, true OA 77%, False OA 41%), with their larger sample of nearly 600
(half OA, half NOA) in Biology (and even lower, near-chance performance
in Sociology, sample size 600, d' 0.11, bias 0.99, true OA 53% false OA
49%) compared to Hajjem et al., who had found with their smaller Biology
sample of 200 (d' 2.45, beta 0.52, true OA 93%, false OA 16%).

Hajjem et al. have now re-done the hand-testing on a still larger sample
(1000) in Biology, and we think we have identified the reason for the
discrepancy, and demonstrated that Hajjem et al.'s original estimate of
the robot's accuracy was closer to the correct one.

The discrepancy was because Antelman et al. were hand-checking a sample
other than the one the robot was sampling: The templates are the ISI
articles. The ISI bibliographic data (author, title, etc.) for each
article is first used to automatically trawl the web with search engines
looking for hits, and then the robot applies its algorithm to the first
60 hits, calling the article "OA" if the algorithm thinks it has found
at least one OA full-text among the 60 hits sampled, and NOA if it does
not find one.

Antelman et al. did not hand-check these same 60 hits for accuracy,
because the hits themselves were not saved; the only thing recorded
was the robot's verdict on whether a given article was OA or NOA. So
Antelman et al. generated another sample -- with different search
engines, on a different occasion -- for about 300 articles that the
robot had previously identified as having an OA version in its sample,
and 300 for which it had not found an OA version in its sample; Antelman
et al.'s hand-testing found much lower accuracy.

Hajjem et al.'s first test of the robot's accuracy made the very same
mistake of hand-checking a new sample instead of saving the hits, and
perhaps it yielded higher accuracy only because the time difference
between the two samples was much smaller (but the search engines were
again not the same ones used). Both accuracy hand-tests were based on
incommensurable samples.

Testing the robot's accuracy in this way is analogous to testing the
accuracy of an instant blood test for the presence of a disease in a
vast number of villages by testing a sample of 60 villagers in each (and
declaring the disease to be present in the village (OA) if a positive
case is detected in the sample of 60, NOA otherwise) and then testing the
accuracy of the instant test against a reliable incubated test, but doing
this by picking *another* sample of 60 from 100 of the villages that had
previously been identified as "OA" based on the instant test and 100 that
had been identified as "NOA." Clearly, to test the accuracy of the first,
instant test, the second test ought to have been performed on the very
same *individuals* on which the first test had been performed, not on
another sample based only on the overall outcome of the first test,
at the whole-village level.

So when we hand-checked the actual hits (URLs) that the robot had
identified as "OA" or "NOA" in our Biology sample of 1000, saving all
the hits this time, the robot's accuracy was again much higher:
d' 2.62, bias 0.68, true OA 93%, false OA 12%.

All this merely concerned the robot's accuracy in detecting true OA.
But our larger hand-checked sample now also allowed us to check whether
the OA citation advantage (the ratio of the average citation counts for
OA articles to the average citation counts for NOA articles in the same
journal/issue) was an artifact of false OA:

We accordingly had the robot's estimate of the OA Advantage of OA over
NOA for this sample [(OA-NOA)/NOA = 70%], and we could now partition this
into the ratio of the citation counts for true (93%) OA articles to the
NOA articles (false NOA was very low, and would have worked against an OA
advantage) versus the ratio of the citation counts for the false (12%)
"OA" articles. The "false OA" advantage for this 12% of the articles
was 33%, so there is definitely a false OA Advantage bias component in
our results. However, the true OA advantage, for 93% of the articles,
was 77%. So in fact, we are underestimating the OA advantage.

As explained in previous postings, the purpose of the robot studies is
not to get the most accurate possible estimate of the current percentage
of OA in each field we study, nor even to get the most accurate possible
estimate of the size of the OA citation Advantage. The advantage of a
robot over much more accurate hand-testing is that we can look at a much
larger sample, and faster -- indeed, we can test all of the articles in
all the journals in each field in the ISI database, across years. Our
interest at this point is in nothing more accurate than a rank-ordering
of %OA as well as %OA citation Advantage across fields and years. We will
nevertheless tighten the algorithm a little; the trick is not to make the
algorithm so exacting for OA as to make it start producing substantially
more false NOA errors, thereby weakening its overall accuracy for %OA
as well as %OA advantage.

Stevan Harnad
Received on Tue Mar 28 2006 - 00:54:20 BST

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