How “Science” Counts Bears

Guest essay by Jim Steele, director emeritus, San Francisco State University

The Inuit claim “it is the time of the most polar bears.” By synthesizing their community’s observations they have demonstrated a greater accuracy counting Bowhead whales and polar bears than the models of credentialed scientists. To estimate correctly, it takes a village. In contrast the “mark and recapture” study, which claimed the polar bears along South Beaufort Sea were victims of catastrophic global warming and threatened with extinction, relied on the subjective decisions of a handful of modelers.

In mark and recapture studies, the estimate of population abundance is skewed by the estimate of survival. For example, acknowledging the great uncertainty in his calculations of survival, in his earlier studies polar beat expert Steven Amstrup reported three different population estimates for bears along the South Beaufort Sea. If he assumed the adult bears had an 82% chance of surviving into the next year, the models calculated there were 1301 bears. If survivorship was 88%, the abundance climbed to 1776 bears. If he estimated survivorship at a more robust 94%, then polar bear abundance climbed to 2490.1 Thus depending on estimated survival rates, a mark-and-recapture study may conclude that the population has doubled, or that it has suddenly crashed.

Here are the simplified basics of estimating survival.

Assume the fenced-off area is your study area. For statistical reasons you ignore observations outside that designated area. During the first year, you reach into your study area and capture four bears, which you then mark by painting a big white cross on their chests. (Researchers first painted big numbers on polar bears for easy identification from a helicopter, but the tourism industry complained that it ruined photographs. They now use discreet ear tags and a tattoo under their upper lip in case the tag falls off.)

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The next year you return to your study area and randomly capture four more bears. However, only two are marked with a white cross. Now the researcher must decide what happened to the two missing bears that were marked last year. Did they die or did they avoid detection? Assuming they avoided detection, then survival is estimated to be 100%. Since the two recaptured bears represent half of last year’s marked bears, the models assume the four bears captured during the study’s second year similarly represent about half of the total population. So the models estimate that there were at least eight bears within the study area.

clip_image004However the calculations change if the researcher assumes the missing marked bears died. In this case, it means that in the second year you captured every possible marked bear. So your model assumes that you also captured every possible bear in the study area. Now the model estimates that there were only about four bears living in your study area. Because the survival rates are greatly affected by this guesswork, these estimates are called “apparent survival rates.”

Apparent survival rates are heavily biased by any migration in and out of the study area. The earliest mark and recapture models were tested on rodent populations, and the statisticians warned that barriers should be erected to prevent the rodents from moving. Otherwise all statistical calculations were totally unreliable. But that tactic is impossible for highly migratory polar bears.

Unlike other species that defend a territory with reliable resources, polar bears never defend territories. They walk and swim across great distances and will congregate wherever the Arctic’s ever-shifting food supply becomes most abundant. A study of radio-collared female bears denning on Wrangel Island determined that after the bears left the island they travelled an average distance of about 3700 miles.2 Although much of their travel is confined within a less extensive region, one radio-collared female was observed in Alaska in late May and tracked to Greenland by early October.3 Such wide-ranging movements allow rapid adjustments to the Arctic’s annually varying food supplies. However it presents great difficulties for any mark and recapture study. Deciding if a bear was travelling or died thus becomes guesswork, and the amount of guesswork increases with shorter studies.

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Instead of erecting barriers, a small percentage of female bears are equipped with radio collars. (Males have such big necks the collars will slide off. Young bears outgrow their collars too quickly and could choke themselves to death. So typically only adult females are collared.) Because collared bears can be tracked, there is no guesswork unless the batteries die. If a radio-collar remains in one spot for a long time, researchers locate the collar and determine if the bear died or just lost the collar. The vastly more accurate survival-rate data produced by collared bears is called “biological survival”. Researchers normally use biological survival to evaluate the accuracy of “apparent survival”. For example, if a large percentage of collared bears survived but simply moved out of the study area, then researchers assume a similar percentage of marked bears had also moved away. In that case, a low apparent survival rate was an illusion due to temporary migration and the avoidance of detection, not death.

Amstrup diligently followed up his earlier study on the apparent survival of South Beaufort Bears using radio-collared bears over a 12-year period. It turned out that his high-end apparent survival estimate of 94% was still too low. If only natural deaths were used, polar bears had a 99.6 % biological survival rate.4 Most bears died at the hands of hunters. If death at the hands of hunters was also considered, then biological survival was still higher than apparent survival, but fell to 96.9%. In 2001 Amstrup concluded that the South Beaufort Sea population was increasing and the current hunting quotas insured a growing population.

To appreciate the magnitude of the problem in estimating apparent survival rates, imagine a human mark-and-recapture study in which the local supermarket is your study area. For statistical reasons, you can only use observations inside your defined study area to determine whether or not your neighbors are alive or dead. (Because you recognize your neighbors’ faces, there is no need to add ear tags or body paint.) How often do you see your neighbors in that store? Although my neighbors and I shop at the same supermarket 2 or 3 times each week, 50+ weeks a year, I don’t see 90% of them at the supermarket more than once every 5 to 10 years. If I was doing a human mark and recapture study, and did not see my neighbors after 5 years, my model would assume most of my neighbors had died! For that reason mark and recapture studies must persist for several years in order to estimate the probability of marked animals being alive but not observed. Otherwise they will underestimate survival. Amstrup warned ““Models that predict rapid increases or decreases in population size would not mirror reality”

Perhaps it was the growing pressure from adversarial lawsuits, and speculation that the polar bears were endangered from CO2 warming, but in a subsequent series of USGS publications coauthored by Amstrup, they suddenly emphasized the illusion of apparent survival and downplayed biological survival to suggest the polar bears were facing extinction. The study was far too short to reliably estimate survival. Still during the first three years of their “extinction” study, the researchers reported apparent survival ranging from 92‑99%574. The higher estimate was the same as the biological survival rates of Amstrup’s radio-collared bears. However apparent survival dropped dramatically for the last two years of the study. The final years of a study always underestimate survival because newly marked are less likely to be observed a second time relative to bears marked in the first years of a study. Claiming “radiotelemetry captures present methodological difficulties” they oddly excluded radio-collared data from critical statistical tests!5 Despite knowing that biological survival rates had never rapidly changed before, and despite knowing more collared bears migrated outside their study area in 2004 and 2005, the USGS report argued polar bear survival had abruptly dropped from 96‑99% in 2003, down to 77% in 2004.6

In their first USGS report, the authors demonstrated high integrity in their analyses and were upfront about the problems of their models, writing, “the declines we observed in model-averaged survival rates may reflect an increase in the number of “emigrants” toward the end of the study, and not an actual decrease in biological survival”, and they noted male bears had exhibited unusually high transiency.5 When apparent survival rates were high, only 24% of the collared females had wandered outside the study area. In contrast during last two years of the study when apparent survival plummeted, the number of collared bears wandering outside the study area had nearly doubled to 47% in 2005 and 36% in 2006, but they never published their biological survival rates. They chose to dismiss the high percentage of bears migrating out of the study area and subjectively chose to argue fewer captured bears meant more dead bears. The authors oddly argued that using 18 years of data the bears are eventually observed in the study area. In keeping with my human/supermarket analogy, it was the equivalent of labeling all your neighbors dead if you don’t see them in the market over a two year span, because over a ten year period you always see them at least once. We need Steve McIntyre to do a polar bear audit!

The dramatic drop in survival meant 400 bears suddenly died but there were no carcasses. To support their unprecedented claims, one USGS report emphasized in the abstract that subadult males showed reduced body condition and that was evidence of nutritional stress that lowered survival.7 However if you read the results section and did some math, you discover that subadult males only represented 5% of all captures. The other 95% were stable or improving. In contrast, adult females represented about 34% of all captures, and despite being under the most stress due to an eight-month fast while giving birth and nursing their cubs, their body condition had improved. That good news wasn’t ever mentioned in the abstract, you had to search the results section: “There was no trend in mass of adult females during the study, but the mean BCI [body condition index] of females increased over time”.7

Their abstract also implied “a decline in cub recruitment” to support their model’s uncharacteristic dip in survival rates. But that too was an illusion. Recruitment compares the number of cubs in the spring with the number of cubs in the fall. Using older studies their observed results found that the number of cubs per female had increased between 1982 and 2006 during the spring. This would be expected. When the female body condition increases, they usually produce more cubs.8 To counteract that good news, the authors then argued there was a decline in cubs during the fall, and thus a decline in recruitment. However they had not surveyed in the fall since 2001.7 They were using deceptive zombie data to support a bad model.

That is how global warming advocates counted bears to refute the claims of the Inuit. That was the driving evidence that led to the uplisting of the polar bear as threatened species. Based on such studies Dr. Derocher, chairman of the IUCN’s Polar Bear Specialist Group (PBSG) warned, “It’s clear from the research that’s been done by myself and colleagues around the world that we’re projecting that, by the middle of this century, two-thirds of the polar bears will be gone from their current populations”.

Don’t count on it!

Jim Steele monitored bird populations on the Tahoe National Forest for 20 years using mark and recapture. Director emeritus, Sierra Nevada Field Campus, San Francisco State University

Adapted from the chapter “Inuit and Illusions in the Time of the Most Polar Bear” in Landscapes & Cycles: An Environmentalist’s Journey to Climate Skepticism

Literature Cited

1. Amstrup, S. C., Stirling, I., and Lentfer, J. W. (1986), “Past and Present Status of Polar Bears in Alaska,” Wildlife Society Bulletin, 14, 241–254.

2. Garner, G. et al. (1994) Dispersal Pattersn of Maternal polar bears from the denning concentration on Wrangel Island. Int. Conf. Bear Res. and Manage. vol. 9, p. 401-410.

3. Durner, G., and Amstrup, S. (1995) Movements of a Polar Bear from Northern Alaska to Northern Greenland. Arctic, vol. 48, p. 338– 341

4. Amstrup, S. and Durner, G. (1995) Survival rates of radio-collared female polar bears and their dependent young. Canadian Journal of Zoology, vol. 73. P. 1312‑1322.

5. Regehr, E.V., Amstrup, S.C., and Stirling, Ian, 2006, Polar bear population status in the southern Beaufort Sea: U.S. Geological Survey Open-File Report 2006-1337, 20 p.

6. Regehr, E., et al. (2010) Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice. Journal of Animal Ecology 2010, 79, 117–127

7. Rode, K. et al. (2007) Polar Bears in the Southern Beaufort Sea III: Stature, Mass, and Cub Recruitment in Relationship to Time and Sea Ice Extent Between 1982 and 2006. USGS Alaska Science Center, Anchorage, Administrative Report.

8. Derocher, A., and Stirling, I., (1998) Offspring size and maternal investment in polar bears (Ursus maritimus). Journal of Zoology (Lond.) vol. 245, p.253–260.

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Harold Ambler

Thank you.

johnmarshall

Very interesting, thanks.
So, there are lies, damn lies and bear stats.

Txomin

Thank you essay, indeed. These kinds of frauds should be prosecuted.

Very good post. Thanks

Joe Public

If you’ve been captured once, experience gained helps you evade recapture.

Peter Miller

Just another excellent reason why it is so important to spend trillions of dollars on ‘climate change’.
Data can be manipulated by statisticians to prove whatever you want, which is about the only thing you can be sure of in ‘climate science’.

A demographic study of radio-collared professors should yield even more shocking results.

Thanks, Jim.

Alan D McIntire

“If only natural deaths were used, polar bears had a 99.6 % biological survival rate.”
That can’t be right. With a 99.6 survival rate, an average bear’s life expectancy would be
100/0.4 = 250 years
” Most bears died at the hands of hunters. If death at the hands of hunters was also considered, then biological survival was still higher than apparent survival, but fell to 96.9%”
That would give a life expectancy of 100/3.1 = 32.26 years, plausible, but I think that would still be pretty high for creatures in the wild.

commieBob

I haven’t read past the first couple of paragraphs and seen a couple of illustrations. This post set off my crap-o-meter.

… which you then mark by painting a big white cross on their chests.

Polar bears are white folks. Polar bears are always white except when they come out of their dens and are dirty white. You can’t identify them by painting them with white paint. Whoever produced this post clearly isn’t intimately familiar with polar bears.
Notwithstanding the above, this isn’t a defense of the polar bear scientists. I have known some and they’re not nearly as stupid as some people paint them. I have also known some of the Inuit. Neither group has a lock on the truth. In spite of the fact that there are no trees to hide them, polar bears are hard to count. They’re white, the snow is white, the sky is often white, the bears are invisible.
REPLY: Note, the title says “bears”, which include white, brown, black, and the occasional pink bear – Anthony

Geoff Sherrington

How science counts sheep.
A man was driving his shiny new BMW and came across a farmer and a huge flock of sheep. He told the shepherd, “I will bet you $100 against one of your sheep that I can tell you the exact number of sheep in this flock.”
The shepherd thinks it over; it’s a big flock so he takes the bet. The driver pulls out his WiFi laptop, gets a a pattern recognition count working on Google Earth.
Inside 3 minutes, “It’s 973,” says the man. The shepherd is astonished, because that is exactly right. He says “OK, I’m a man of my word, take an animal.” The man picked one up and began to walk away.
“Wait,” cried the shepherd, “Let me have a chance to get even. Double or nothing that I can guess your exact occupation.” The man thought for a moment a said “sure.”
“You are a top economist for the federal government,” said the shepherd.
“Amazing!” responded the man, “You are exactly right! But tell me, how did you deduce that?”
“Well,” said the shepherd, “Put down my dog and I will tell you.”

stan stendera

I love polar bears. I think they are one of the ecological marvels of the age. That being said I would not want to meet one in a dark alley without a large gun in my hands, and even then I would not be sure of my survival. That is why in a nutshell they are an ecological marvel of the age.

There ought to be some sizable differences in male vs female travels. Perhaps people could get a grant from Coca Cola to come up with a good radio tracking harness for males.
I know some human females who’d like a radio tracker for their males….

Gaudenz Mischol

“Polar bears are white folks. Polar bears are always white except when they come out of their dens and are dirty white. You can’t identify them by painting them with white paint. Whoever produced this post clearly isn’t intimately familiar with polar bears.”
If you read carefully you will see that this is thought as an example and has nothing to do with the studies mentionend

Alan Watt, Climate Denialist Level 7

Very interesting and informative. Thank you.
You mentioned changes to marking techniques due to complaints from the tourist industry (polar bear safaris, I assume). Did anyone think to correlate data from the tourist industry? If bear populations are declining I would expect that to mean fewer sightings on these safaris.

Once again, this reminds me of the statistics course I had to take in college. Early on in the class, we were taught how to make stats lie while still telling the truth. That is the only thing I remember from that class because because I didn’t need statistics for my computer science degree.

kakatoa

Dr. Steele,
Thank you for an insightful post. I concur with the overview of your new book
“Landscapes and Cycles will enlighten anyone concerned with climate change and the fate of endangered species. Not only is it fascinating reading for the general public, it should required reading for every high school and college environmental studies class.”

Alberta Slim

Obama and the EPA are closing Coca Cola f because they are producing product that is releasing CO2 into the atmosphere, causing CAGW ;^)

commieBob

Gaudenz Mischol says:
July 3, 2013 at 5:21 am
… If you read carefully you will see that this is thought as an example and has nothing to do with the studies mentionend

At some point it is important to understand your subject material. No matter how good your logic and statistical methods, you can still arrive at absolutely laughable conclusions if you don’t understand the material. Geoff Sherrington makes the point elegantly.

Geoff Sherrington says:
July 3, 2013 at 5:05 am
How science counts sheep. … “Well,” said the shepherd, “Put down my dog and I will tell you.”

What I said was: “Whoever produced this post clearly isn’t intimately familiar with polar bears.” I stand by that unless someone can produce evidence to the contrary.

William McClenney

So, sadistics, again…..
Thanks Dr. Steele.

commieBob says: I haven’t read past the first couple of paragraphs and seen a couple of illustrations. This post set off my crap-o-meter. … which you then mark by painting a big white cross on their chests.
Of course polar bear are white, and I was worried the brown bears may confuse some, but the illustrations are meant to show how any mark and recapture works.

Gary

The difference between the Inuit and scientists, as far as estimating polar bear population size is concerned, is that one group is expert and the other amateur. Always consider the source of information when judging its value. Meta-data are important.

Jim Steele, this is a great article. Ignore the noisy drunk in the back of the bar.

commieBob [July 3, 2013 at 5:01 am] says:
commieBob [July 3, 2013 at 5:51 am] says:

Sleep it off and then ask one of the moderators to strike those two posts. You’ll be thankful later.

The American Libertarian refers to these times as “the time of much fudged data”.

Mike Bromley the Canucklehead

Why would they be trying to refute the Inuit? I mean, after all, what do the Inuit know? There’s no point in trying to refute them, it’s a waste of resources that could be better spent staying south of the Arctic Circle, employing robust models and making videos of polar bears raining from the sky.

Chris4692

commieBob says:
July 3, 2013 at 5:51 am

What I said was: “Whoever produced this post clearly isn’t intimately familiar with polar bears.” I stand by that unless someone can produce evidence to the contrary.

The thought expeiriment example does not mention the type of bear. In the illustration the bears are clearly not white, so presumably not intended to be specifically polar bears. The type of bear is clearly not important to the example.

Lyle

Zak Unger’s book “Never Look A Polar Bear In The Eye” relates some of the biases that biologists like Amstrup hold.

@ Alan D McIntire. That would give a life expectancy of 100/3.1 = 32.26 years, plausible, but I think that would still be pretty high for creatures in the wild.
Your math is good. Typically bears over 20 years old are labeled as “senescent”. It is hard to definitively determine their natural longevity as trophy hunters sought the biggest bears a bush pilot could fine. With modern hunting regulations percentage of bears over 20 years as risen. Based on “harvested bears” in the western Hudson Bay, 5% of the population in 1985 and 15% in 2003 were bears older than 20 years. I haven’t seen a recent study that breaks down each age.but a 1988 study reported 2 out of 52 captured bears 24 years or older. Based on Canadian Wildlife Service mark and recapture older bears make up 8 to 9% of the population

kent Blaker

“It’s clear from the research that’s been done by myself and colleagues around the world that we’re projecting that, by the middle of this century, two-thirds of the polar bears will be gone from their current populations.”
Only 2/3? it is about 40 years before the middle of this century. Of the current population of polar bears how many will be alive in 40 years.?

Excellent essay Jim!
Very clearly presented and exceptionally useful.
I’d like to reblog this at PolarBearScience, if you don’t mind. It would make an excellent companion piece to my post from yesterday http://polarbearscience.com/2013/07/02/did-polar-bear-numbers-in-e-beaufort-fluctuate-each-decade-due-to-thick-ice-years/ and the follow-up later this week about Southern Beaufort polar bear studies.
Susan

@ Susan
Yes of course. I was going to pull another essay from the book on the effects of sea ice that would also fit support your article at PolarBear Science. It was the heavy ice years that detrimentally affected the ringed seals and thus the bears, even the CO2 advocates acknowledge that. For example Ian Stirling, PBSG expert, Canadian Wildlife Service wrote “Heavy ice conditions in the mid-1970s and mid-1980s caused significant declines in productivity of ringed seals, each of which lasted about 3 years and caused similar declines in the natality of polar bears and survival of subadults, after which reproductive success and survival of both species increased again.”

@commieBob
Obviously your intent is to discredit the essay versus discuss the validity of the methods or my critique. You remind me of the critics of Pixar’s “Its a Bug’s LIfe”. They denigrated the artists for portraying ants with only 4 legs and not accurately portraying the correct anatomy. As if that mattered when the ants were talking Engilsh. So to be clear, giant hands are not used to sample bears either.
If the color threw you I don’t expect you to understand the grave implications of the bad model and skewed presentation of data which is the important point

Thank you Jim, a good informative piece. And for all of you interested in the colour of Polar bears, their skin is actually black. Not many people know that …
Pointman

Steve Oregon

How many times in how many more ways will the Climate Brigade be shown to have colluded to present entirely false data and conclusions before they are suffocated under embarrassment and shame?
Just wondering.
It would seem they are approaching sufficient exposure.
What single or several things would be a nice trigger?
A ClimateGate III with Mann, Schmidt & Hansen caught ginning up tall tales?
Or did that already happen?

Jack Simmons

The real reason polar bears are thriving:
http://www.cocs.com/imagegallerydetail.asp?ImageID=516

Mikeyj

kent Blaker says:
July 3, 2013 at 6:44 am
“Only 2/3? it is about 40 years before the middle of this century. Of the current population of polar bears how many will be alive in 40 years.?”
Probably not 2/3 of the readers here today either.

jlurtz

Is there anything that we have been taught that is correct? I mean anything about anything!

Reblogged this on makeaneffort and commented:
Please, please, please read this.
It’s applicable to almost everything Scientists predict or “guess” at.
It should leave you with the question… “If “guessing” or “assuming” is required, then why not guess or assume the outcome which best fits consciously, or unconsciously, desired outcome?”
Remember, Bias is everywhere. It is unavoidable.
Where it should not be is in Science. But when your next years funding depends on a certain outcome…

JohnWho

@Dr. Lurtz
Of course there is.
Hold on while I Google that, I am sure I will find something…

JohnWho

Still searching…

JohnWho

Uh, Google says to try Bing.
Binging now…

KNR

The endlessly changeable ‘standards ‘ of climate science ‘ deals with this easily ‘native wisdom’ is wonderful thing when it supports ‘the cause ‘ but when it does not its meaningless rubbish as their not ‘climate scientist’ and can only see the local picture .

DonS

In the world of the hunter a dog which chases the wrong species is said to exhibit unsatisfactory behavior and lack attention to the task at hand. Think of a stag hound chasing a raccoon. The stag hounds posting here should stop chasing commieBob.

JohnWho

Bing put me on it’s “Subversive watch list”!
Maybe someone else can help.

eyesonu

Alan D McIntire says:
July 3, 2013 at 4:54 am
Re: lifespan of bears in the wild
=================
http://wiki.answers.com/Q/What_is_the_lifespan_of_a_bear
Seems that bears have a life expectancy of over 30 years in the wild. Hunting would likely target the largest and therefore likely the oldest individuals. It would be like harvesting a resource just prior to the eventual waste (death) by natural cause.
—-
This is an excellent article by Prof Jim Steele. Thank you.
If Steve McIntyre were to find time and the inclination to deal with this in his analytical manner and co-author a paper with Steele and Amstrup, the polar bears crises could be laid to rest. That would certainly ease the minds of those fearing for the safety of polar bears, I would hope. 😉

… by the middle of this century, two-thirds of the polar bears will be gone from their current populations”.
================
Duh! The lifespan of polar bears is 45 years max, so it is quite likely 2/3 of those alive today will be dead in 40 years.
Great article. Hopefully the census bureau will start a catch and release program soon in the local supermarkets to replace that nuisance questionnaire they have you fill out regularly under pain of death or worse – endless hounding phone calls as soon as your sit down to dinner.
Fishermen have relied on catch and release for years. Every time they come home after a “fishing” expedition there is infinite opportunity to tell tales of the humongous fish they caught, only to have to let it go under “catch and release”. Glad to see $cientist$ have caught on. Infinite opportunity to catch and release bears as well as fish.

LamontT

Ah computer models. Unfortunately the public isn’t cautious about them and appear to believe that it is possible to accurately predict the future with a computer.
Can a model be helpful for trying to figure out what is going on? Certainly, but they can’t accurately predict the future like a crystal ball.

Is it racist of me to ask why the polar bears in the drawings aren’t white?
I don’t think your supermarket analogy is quite right, I see my neighbors a lot more often in my neighborhood than I do at the supermarket, even though I know they must go there at least once a week. The supermarket is a place we migrate to and from, isn’t the place we live, or if you like it is our hunting grounds ,but we always return home.
This way of “counting” reminds me of Bush V.S. Gore where statisticians claimed that Gore must have won, even though two actual counts showed he did not. Then of course Gore later went on to claim that the center of the earth was millions of degrees.

markx

commieBob says: July 3, 2013 at 5:01 am
…..and his over sensitive crap-o-meter.
Ah, Bob, you are such a joker! Jim Steele clearly mentions how the bears are really marked, and that “painted cross” is clearly just a tongue in cheek simplified phrase to fit the neat explanatory cartoons … (though, perhaps not simple enough for some).
“….use discreet ear tags and a tattoo under their upper lip in case the tag falls off….”
BTW, Great article, Jim Steele, I enjoyed the read; very educational and very well explained.

juan slayton

Dr. Steele,
If I understand correctly, the last PBSG census put the bears into 19 different population groups, and offered a map of their respective areas. The extreme migratory range that you describe in this post raises a question in my mind of how such grouping can have any validity. I’d like to know your opinion.