# PennHip vs OFA article



## CelticKitti (Jul 1, 2010)

Hip Dysplasia Susceptibility in Dogs May Be Underreported, According to Penn Vet Comparative Study | Penn News

Was wondering if anyone else had read this and what your thoughts were. If not here you go!

I'm leery of taking this to much to heart because PennHip has the potential to benefit financially from this research. They could have presented it so that it looks the best for them.

I really think there needs to be a head to head study funded by an outside source. Dogs should be tested with both methods and followed through their lifetime to determine which dogs really develop HD. This would be a VERY HARD and EXPENSIVE study!! If we really are going to see which is "better" and more accurate this is the only way I see it happening. 

I'm not an expert but just a thought. Am currious of what others think.


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## CelticKitti (Jul 1, 2010)

I would love to read the actual journal article published in the AVMA journal but I don't have access to it.


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## ziggylu (Jun 26, 2010)

I am able to access the original article in the JAVMA. If you would like me to send you a copy, please send me your email via PM.


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## Feralpudel (Jun 28, 2010)

ziggylu said:


> I am able to access the original article in the JAVMA. If you would like me to send you a copy, please send me your email via PM.


Ziggylu, I sent Celtickitty a copy of the article. But it's good to know that somebody else has access, lest I wear out my welcome with my brother.


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## Feralpudel (Jun 28, 2010)

A friend sent me this abstract the other day. I've been busy with work, of all things, and finally got around to reading the actual article today. 

This article annoys me in so many ways, I am tempted to use it in a research methods course I teach. 

Long story short, as best I can tell, there is a longstanding academic pissing match between OFA and Pennhip in the veterinary literature, but no really good, definitive study that compares the two methods head to head. You might think from reading the abstract that this is that study, but it is not, IMO, for reasons I'll go into in a moment. The study is by the Pennhip guys, and--quelle surprise--they find that the Pennhip method is much better at detecting dogs at risk of developing osteoarthritis later in life (and by extension, of passing on risk of HD to their offspring). 

They do this by looking at the relationship between DI scores<.30 and OFA scores. They look at dogs that are OFA fair, good, and excellent, and if those dogs have DIs >30, then they consider those OFA false negatives. (A false negative is when a test indicates you are clear of something when you're not.) 

The first problem with this is that they assume that they, Pennhip, are the gold standard--the test by which the other test is to be judged. Given that OFA is the much older, more widely used test, that is a strong assumption in the absence of clear evidence of greater predictive validity of Pennhip. 

The second, related problem is their use of .30 as the magic cutoff point between acceptable and unacceptable hips. Why .30? Because Pennhip has determined that a dog with a DI of less than .30 has virtually no risk of developing hip OA. That's nice to know, but if you use that as a hard cutoff for breeding decisions, a number of breeds would go extinct. You can see that from Pennhip's own mean DIs for some breeds, including spoos. I include here the means and the standard deviations (SDs). The SDs are useful because if you assume a normal distribution, you can subtract one SD from the mean and assume that only approximately 15% of the population falls below that value. You can subtract 2 SDs from the mean and assume that only about 2.5 percent of the population falls below that value, i.e., has hips with a DI less than that value. So, for example, if a breed has a mean DI of 60 (Newfoundland) and a SD of 16, then only 15% of Newfies have hips with a DI of less than 44! The other thing to remember is that these are all dogs considered potential breeding stock, i.e., they had hips done. 

So here are some breeds with mean DIs and SDs. (Some of these come from this article, while some come from another Pennhip article I have on four breeds, including spoos):

Golden retriever .50 (.11)
Labs .48 (.14)
Rotties .45 (.12)
Am. Bulldogs .55 (.14)
Bernese Mtn Dog .55 (.16)
Newfies .60 (.16)
Std Poodles .49 (.13)

The Pennhip folks argue that you improve hips over the generations via selection pressure. The more pressure, i.e., the more stringent your criteria for which hips you'll use (e.g., only DIs under 30), the faster hips will improve in the breed towards greyhound quality hips (greyhounds tend to have excellent hip conformation). But as you can see above, that stringent a criteria implies using only a tiny percentage of the dogs in a breed that are considered potential breeding stock, e.g., 12 percent of those who get hip x-rays to begin with. That *might* be worth doing if you have a breed with a very broad gene pool and crappy hips. Otherwise, your gene pool is going to take a huge hit, and you're going to "pressure" some breeds right out of existence. 

Now, I would have a little more respect for this approach if the Pennhip folks put their money where their mouth was, and actually used .30 as a hard cutoff in their reports to owners. But of course, they don't--they emphasize where your dog is vis a vis other dogs in the same breed, and encourage breeders to use stock in the tightest half. Using the median as a suggested cutoff is a lot different from using the top 10% as a cutoff! They are quick to call OFA acceptable dogs with DIs >30 "false negatives," but by their own logic, they are also encouraging the use of a lot of potentially problematic dogs. 

So sorry to geek out on everybody like this! Geez...you sign on for a little poodle fun and find yourself in a stats class. But this sort of crap in journals really bothers me. It especially bothers me given that IMO, we have a small problem with HD in spoos and a huge problem with genetic diversity. We can't afford to be throwing the baby out with the bath water.


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## ziggylu (Jun 26, 2010)

Heh. I haven't actually read the article, but I appreciate your rant from a methods point of view. I"m a very applied person and so much of what goes on in academic research drives me crazy, even as I work towards becoming part of the problem myself. 

Your points about genetic diversity are well taken. Animal genetics is not anywhere related to what I study but I do study resilience and adaptive capacity of systems from a sustainability context. Anytime diversity is removed from the system, overall resilience and sustainabilty of the given system will suffer. Doesn't matter what the system is.


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## CelticKitti (Jul 1, 2010)

Yes I have the full article but I have not had a chance to sit down and read it yet. From a quick overview I was not pleased with the methods either. I'll try to get my thoughts posted for those who are interested. 

Don't worry Feralpudel I'll proboblay geek out too!


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