Deltoid

Steve D. Fischer writes:

Now, you've got 100 lines to convince me WHY I should risk getting myself into trouble with the law, when all I wanted to do was report a crime that happened to me.

The trouble is that Kleck would have you believe that this accounts for the discrepancy between his survey, that is, 97% of DGUs are by people who think they would get in trouble for it AND that these people would tell his interviewer but not one working for the NCVS. That is 97% of the population simultaneously believe that the government will lie to them (by promising confidentiality) and that the government would not lie to them (by pretending to be an interviewer working for Kleck). This is absurd.

I think the 97% figure is way too high, also. I have no problem with 50% though.

If it is 50% then the NCVS underestimates by a factor of 2 i.e. this implies 160,000 DGUs.

It's all just guesswork. The only way to get at this is to build in some kind of "lie scale" into the survey. You have to find some way to get at the respondent's level of trust of the government - you can't do that in a government survey, however, like the NCVS. As for "making up" DGUs, I have no crystal ball for estimating the magnitude of this. Perhaps you have some suggestions?

85% of Kleck's DG users reported that they personally (rather than some other household member) used the gun. The average household size is just slightly under 2, so only 51% of uses should be personal rather than household ones. The discrepancy may be because people are more likely to make up DGUs about themselves rather than others. If this is true, the difference between 85 and 15 (the number that would be equal to the number of DGUs by other household members) are "made up" DGUs. I.e 70% of Kleck's DGUs are made up, implying 450,000 DGUs after correcting for "made up" ones.

160,000 vs 450,000 is still an enormous gap, but at least they're closer....

You see, the NCVS has a problem too. Kleck reported 213 DGUs in a 5000 interview sampling. The NCVS interviewed something like 65,000 people as I recall, and "found" 80,000 DGUs. If you assume the NCVS is God's honest truth, then Kleck should have found only 7 DGUs in his sample of gun owners. That means 206 people lied.
That's only 4.1% of Kleck's sample. Lying on that scale is certainly not hard to accept, but this still poses a problem for the NCVS.

The NCVS should have found something like 88 DGUs if you assume, as Kleck did, that there are 59 million gun owners in the USA. If you also assume that the same number of people lied to the NCVS as lied to Kleck (4.1%), then 2665 people should have reported a DGU to the BJS! Both surveys used random sampling, and the number of households owning guns (48%) is large. There is no reason, a priori, to assume that more people would invent DGUs to a greater degree in one poll than the other.

So where are the missing liars in the NCVS poll?

Are we to believe that the NCVS filters out 97% of the liars who wrongly report DGUs? I find that rather hard to believe, and I'll bet you do too?

They may lie and and make up crimes, but not necessarily invent the detail of gun defence in their fictional crime.

Some people will keep quiet about DGUs, but they're not going to tell Kleck either.

Well, now that's the crux of the matter, isn't it? It all hinges on two differences between face to face polls versus phone polls.

No, because the NCVS is mostly conducted by phone. (Some interviews are face to face but the great majority are over the phone.)