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roachboy · 12-19-2005, 06:57 PM

did anyone actually read the report? i am going through it now--the definition of "center" is really quite odd, based on voting patterns in congress. so the whole study cuold also be showing that congress is right of the public. duh. but i am still working through and havent yet researched the writers.

search the press release title and you'll find a few versions of the whole thing to look at (pdf, website, etc.)--have a look--potentially a more interesting discussion than what there now is--which amounts to:

"does this press release indicate a study that conforms to your expectations about media biais? and of course there is no reason to note any information about where you get those expectations from..."

caveat lector: i paraphrased a bit.

by the way, here's the defintion itself:

Quote:

Digression: Defining the ?Center?

In discussing left- or right- wing biases of the media, one should be careful how he or she defines center. We think the most appropriate definition refers to a central voter, as opposed to a central member of Congress. Accordingly, we think that it is more appropriate to compare media scores to the House as opposed to the Senate, since the Senate disproportionately represents small states. Next, we think it is more appropriate to use the median House member, instead of the mean. One reason is that, because of The Median Voter Theorem (Black, 1957), one should expect policy to be at the median instead of the mean. Another reason is that comparisons to a mean can be manipulated by the ADA?s choices of roll call votes, whereas comparisons to a median are not subject to such manipulation.

To see this, first note that the ADA has considerable leeway in the roll call votes that it chooses. For instance, suppose it chooses many roll calls such that the cut point of the roll call lies between moderates and extreme liberals. Such a cut point would cause moderates to form a coalition with extreme conservatives on the roll call. (An example of such a roll call would be a bill to ban partial-birth abortions. Here, moderates and conservatives favor the ban, and only extreme liberals oppose it. ) A prevalence of such cut points would cause moderates to have ADA scores more similar to conservatives than liberals. Meanwhile, if it predominantly chose cutpoints on the other side, then the ADA would cause moderates to have ADA scores more similar to liberals than conservatives.

Because of this leeway, with one set of roll calls, the ADA could make a member of Congress or media outlet appear more left-wing than the mean score. However, with a different set of roll calls the ADA could make the same member of Congress or the same media outlet appear more right wing than the mean score. To see this, consider the following example. Suppose there are only five members of Congress. The most left-wing legislator is Member 1, who is more left-wing than member 2, who is more left-wing than member 3, and so on. Suppose media outlet A has an ideology identical to member 2. Consequently, its ADA score (that our method estimates) will be identical to member 2?s score (at least in expectation).

Now suppose that the ADA chooses four roll calls, such that the first roll call has a cut point between members 1 and 2, the second has a cut point between members 2 and 3, and so on. Because the distribution of cut points is uniform, member 1 receives 100 ADA score, member 2 and media outlet A to receive a 75, member 3 receives a 50, and so on. The mean ADA score of the legislators is 50. Thus, this set of roll calls makes media outlet A appear more left-wing than the mean score.

Next, instead suppose that the ADA chooses four roll calls such that each has a cut point between members 1 and 2. This would cause member 1 to receive a 100 score. Media outlet A and members 2, 3, 4, and 5 would receive a 0 score. The mean ADA score in this case would be 20. Thus, this set of roll calls makes media outlet A appear more right-wing than the mean score.

Meanwhile, for this example, regardless of the ADA?s choice of cut points, media outlet A?s score will necessarily be greater than or equal to the median?s score (member 3). That is, unlike the case where we use the mean score as a comparison, it is impossible to make media outlet A appear more right-wing than the median score.

The point of this example is not to suggest that the ADA might intentionally choose roll calls to manipulate a legislator?s or media outlet?s perceived ideology relative to the mean. Rather it is to demonstrate an arbitrariness that exists when one uses a mean score for comparison. The same arbitrariness does not exist with median scores. As a consequence, we think it is appropriate to compare the scores of media outlets with the House median, 39.0.