C. Everett's ejectives/altitude correlation is not significant

I've now had a chance to take a closer look at Caleb Everett's recent PLoS ONE article on the correlation between ejective consonants and altitude, and I think the ejective
distribution is explainable on purely classical grounds, that is,
common inheritance and areal diffusion. That is, it is NOT necessary to resort to
an explanation in terms of altitude. The classical explanation is preferable
since the mechanisms of inheritance and diffusion are observable in
plenty, whereas noone has yet observed the hypothesized mechanism whereby
the speakers start using more ejectives in response to moving to higher
altitudes.

Here's why: The UPSID database via WALS contains 527 languages coded
for ejectiveness, with 87 with ejectives (having WALS value 2, 5, 6,
or 8) and 440 without ejectives. The 87 languages with ejectives
belong to 54 families (ejectives_families). The 54 families are not necessarily
independent because some of them are geographically contingent. I
grouped the 87 languages into areas such that the languages within an
area could plausibly be connected by adjacency or via a path of
adjacent languages also known to have ejectives. There is some amount
of leeway here but if there really is a causal link between altitude
and ejectives it should survive nevertheless. The 87 languages divide
into 19 areal groups (listed in ejectives_areal).

Now if we pick languages such that no two of them belong to the same areal
group or the same family, then there are arguably genealogically and areally
independent. Since there are 19 areal groups (and 54 families) one cannot
pick more than 19 independent languages, but it turns out that it is
possible to pick 19 languages which are indeed both areally and
genealogically independent. I picked a random such set, shown below,
together with their altitude (as per the Shuttle Radar Topography Map at
their centre coordinate):

Hadza [hts] 1049
Yapese [yap] 0
Hamtai [hmt] 1175
Hausa [hau] 594
Yuchi [yuc] 263
Trumai [tpy] 312
Southern Nambikuara [nab] 640
Zuni [zun] 2009
Itelmen [itl] 35
Itonama [ito] 156
Michoacan Mazahua [mmc] 3399
Ona [ona] 117
Tsimshian [tsi] 177
Soqotri [sqt] 364
Korean [kor] 158
Shua [shg] 1057
Wichi Lhamtes Guisnay [mzh] 208
Abkhaz [abk] 0
Central Aymara [ayr] 4298

The mean elevation of these languages is 842.6 m and the median elevation 312 m. Is
this higher than expected for "random" languages? I took 1000 samples of
19 languages from different families and checked their mean and median
altitude. 56 of the 1000 random samples had a higher mean altitude than
842.6 m and 296 of the 1000 random samples had a higher median than 312 m,
giving p-values of 0.056 and 0.296 respectively. In other words, NOT
SIGNIFICANT by conventional significance limits.

So why does Everett claim to have controlled for areality and genealogy
and still reports a significant correlation (in his Table 3 and associated
text)? (The remainder of the significance results reported in his paper
treats languages as independent, not controlling for areality/genealogy.)

1. Everett doesn't measure the direct altitude of a language but the
proximity to a "major region" of high elevation. What counts as a
major region is never objectively defined, and clearly there is some
cheating going on when using the distinction "major/non-major" because
the proposed theory (which has to do with air pressure etc) is
oblivious as to whether the speakers are in a "major" or "minor"
region of altitude. The difference is significant because it turns over
many datapoints, so that, e.g., the New Guinea Highlands is not counted
as a high-altitude region!

2. The division of the non-ejective languages into clusters "by assuming
clusters contain ten languages each, in keeping with the approximate size
of the clusters of languages with ejectives" is underspecified. This is
a highly non-trivial step (there are *many* ways to divide non-ejective
languages into clusters containing ten each) and the fact that it is not
explained means that the experiment is not reproducible. If I was the
reviewer I would never have let that through.

3. There is arbitrariness with measures such as 200 km and 500 km from a
major region, and some comments in the paper suggest that data dredging
has taken place. That is, comments of the kind "only marginally further
away from high elevation at 380 km", might reflect that different thresholds
have been tried and 200/500 km are included in the paper because they
happened to give the best results. If so, all p-values should be corrected
for multiple testing. Because of the irreproducibility (as of point 2 above)
I cannot re-do the test with other thresholds than 200/500 km to check.

One should perhaps also not forget that the UPSID database in the first
place is not a random sample of the languages (or families or regions) of
the world and therefore it is not legitimate to draw statistical
conclusions based on it. It would be better to re-check it on Steven Moran's or
Mark Donohue's databases.


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One Response to C. Everett's ejectives/altitude correlation is not significant

  1. One should not forget that the location points for the languages in WALS are another source of potential arrors. The location points are misleading because first they reduce a language's distribution to one point while in most cases it ought rather be an area (which might very well span quite various altitudes) and second because the points were arranged to allow maximum visibility / minimum point overlap.

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