It’s been three days now since “Summer Storm 2003”, as the local media have christened it, and like 175,000 other Memphians, I’m still without power. I’m guessing I’ll be among the last to get power back, since my power line is lying in the middle of my back yard, having been downed by a neighbor's falling tree.

I discovered an interesting fact about homeowner’s insurance: if your neighbor’s tree falls and does damage to your property, your neighbor (or his insurance company) is only liable if the tree was damaged or diseased. Falling tree damage is handled by a negligence rule, not a strict liability rule.

I’m wondering whether this is the correct rule, from the perspective of economic efficiency. Generally, a rule that places liability with the party most likely to prevent an economic harm is the more efficient one. The negligence rule for tree damage shifts some of the economic risk from the tree owner, who could easily trim his trees, to potential neighbor, who can at best choose not to buy property next to people with towering trees.

The negligence rule will be more efficicient, economically, only if there are sufficient positive externalities to having towering trees in residential neighborhoods. There are some externalities, of course. I like living in neighborhood with tall trees, and I get to enjoy this even though there aren’t any tall trees on my property. If enough other people enjoy this as well, this will be reflected in the market value of the property. But are these externalities sufficient to overcome the problem of property owners ignoring tree maintenance, and letting trees grow to the point where they could easily damage the property of others?

Thanks to Kevin of WizBang! and a little bit of cleverness on my own part, you can now manually enter a TrackBack to any post here at Signifying Nothing; just click on the TrackBack link on the entry (it looks like « and has a tooltip saying “TrackBack”), then click on the “Register a TrackBack manually” link. The needed manual URL will be filled in for you; all you need to enter is the post’s permalink URL, the title of your post, an excerpt, and the name of your blog. Ideal for those of you still slumming on Blogger or other weblog tools that don’t support TrackBack.

One of the more bizarre questions revolving around the Iraq war is that there is a large proportion of the American public who believe that Saddam Hussein was involved personally in the 9/11 attacks on the World Trade Center and Pentagon and the foiled attack on the White House.* This belief persists despite there being no evidence of a direct link, no statements by any credible source that there is a direct link, and repeated refutations of a direct link. (Many leftists want to pin this belief on the Bush administration, but I don’t think the charge sticks without showing that Bush et al. deliberately fostered this belief; there’s simply no evidence of that.)

Being a good empirical social scientist, I was curious about who would believe this assertion. Again, I used the second March 2003 CBS/New York Times poll (conducted March 5-7, 2003). The poll doesn’t have much useful data for testing any psychological theories, but a sociological model seemed to work fairly well. I produced both maximum-likelihood (ML) and MCMC estimates; since the ML estimates were basically identical to the MCMC estimates (the missing data problem was less acute in this model), for ease of interpretation I stuck with them. Here are the probit results (I’m too lazy to build a proper table from the R output; sue me):

            Estimate Std. Error z value Pr(>|z|)
(Intercept) -0.01797    0.26186  -0.069 0.945277
pid         -0.09596    0.04594  -2.089 0.036699 *
college     -0.27348    0.14702  -1.860 0.062858 .
male        -0.62078    0.14587  -4.256 2.08e-05 ***
black        0.17079    0.17603   0.970 0.331934
catholic     0.05115    0.11446   0.447 0.654921
jewish      -1.18340    0.49424  -2.394 0.016649 *
atheist     -0.41736    0.14938  -2.794 0.005208 **
haskids     -0.04056    0.10507  -0.386 0.699462
agecat       0.01696    0.05475   0.310 0.756710
libcon       0.25993    0.07314   3.554 0.000379 ***
pid:college -0.10990    0.05790  -1.898 0.057699 .
pid:male     0.12066    0.05629   2.144 0.032059 *
---
Signif. codes:  0 `***' 0.001 `**' 0.01 `*' 0.05 `.' 0.1 ` ' 1
N: 782
Percent correctly classified: 64.83%
Proportional reduction in Error: 27.25%
McKelvey/Zavonia Pseudo-R^2: 0.214

Jewish and atheist voters are significantly less likely than Protestant voters (the omitted reference category) to believe Saddam was personally involved in 9/11, while there is no difference between Catholics and Protestants. Conservatives are significantly more likely to believe in the Saddam-9/11 link than liberals.

The other significant effects are expressed in interactions between multiple variables. I estimated interactions between gender (male) and party identification (pid) and between level of education (college) and party identification. These effects are shown in this graph. The horizontal axis is the respondent’s party identification, where 0 is “strong Republican”, 1 is “independent leaning Republican”, 2 is “true independent”, 3 is “independent leaning Democratic”, and 4 is “strong Democrat.” (Age is set to the mean value; other variables are set to the modal category.)

Males in general, particularly male Republicans, are much less likely than females to believe the Saddam-9/11 link, regardless of education level. However, among Democrats, the primary difference is between the college educated and the less-well educated, with the gender difference being relatively small.

What does this mean? There are a few possibilities. The most compelling one is that people who don’t know are guessing, drawing on some vague association between Saddam Hussein and radical Islam. The demographic variables may be indicators of attentiveness to the media; those who pay more attention to the media may have a more nuanced understanding of Middle Eastern politics. The partisan effects suggest that some voters may be projecting their own belief systems onto the question; strong Republicans may be projecting hawkish attitudes onto questions about Saddam, while strong Democrats may be projecting a belief that Saddam isn’t a threat onto him, at least among the better-educated.

More generally, the results suggest that trying to argue Saddam wasn’t linked to terrorism may be a losing strategy among their own base for Democratic presidential candidates that opposed the war or are having second thoughts now. Strongly Democratic voters without a college education are more likely than not to believe that Saddam was involved in 9/11, and it will be difficult to reeducate them on this point. These findings suggest that however candidates like Bob Graham and Howard Dean try to spin things, many Democratic voters think Saddam Hussein was a legitimate target in the war on terror, and they will cross these voters at their own peril.

Then again, maybe all these people think Saddam was involved in 9/11 because his regime actually was, at least to some degree.

Sorry, I meant to write up the results from the Saddam-9/11 analysis last night so I could post them here today. In the meantime, though, you can look at the pretty graphs. Not sure if they’ll make much sense without the writeup though…