Golden Retriever Dog Forums banner

Comparison of OFA Ratings and PennHIP DI Scores

6K views 5 replies 3 participants last post by  Tagrenine  
#1 ·
Being new to dog-ownership-in-general and owning-goldens-in-particular, I am fairly interested in OFA and PennHIP as it relates to anticipating health concerns with our puppy/dog. And, seeing as it's been a while since this topic was directly addressed on a GRF thread, it seemed like an appropriate time to "stir the pot". 😁

The following table is something I put together, using information from a slightly dated study (but, the only study I found that wasn't on a site that seemed like it might be biased). This study addressed 439 dogs, aged 2-or-older, that were assessed from June '87 to July '08.

875436


Based on my readings on the OFA site, a rating of "Excellent", "Good", or "Fair" is considered "passing". My assumption is that any other rating is considered "failed".

Based on my readings on PennHIP, the "magic number" for the diffraction index (DI) is 0.30. DI's above 0.30 are supposed to indicate an increased risk of hip issues. While I have not seen anything that explicitly correlates at PennHIP DI of 0.30 with an OFA rating of "Fair", most of the information I have found online seems to infer this association.

What I found interesting is that the OFA assessments indicated 84% of the dogs assessed were cleared for hips. The study used the inferred association of a DI of 0.30 to an OFA "Fair" as the line-in-the-sand, with significant numbers of the OFA-certified dogs not meeting the PennHIP metric. I then adjusted the numbers to reflect only those dogs that both met minimum OFA and PennHIP ratings. This resulted in a 5x increase in the numbers of dogs that would not be recommended for breeding.

Since I am not a breeder, this information is less of a concern, although these values greatly increase my interest in seeing how our Kona scores (for purposes of planning for health, and maybe preventative measures if warranted). But, if I were a breeder, I think I'd be concerned about the potential impact of such a significant decrease in the potential pool of dogs for breeding.

Thoughts?
 
Discussion starter · #3 · (Edited)
A DI of .30 would be great. The few dogs I have PH'd coincidentally were also OFA Excellent and one of them was .28/.30 and the other was .29/.30
Reworded in an attempt at clarity...

Part of me wonders "if a mechanism indicates >90% of dogs evaluated are at a higher risk for hip issues", then how should reliable/accurate is that mechanism if "only" 40% of the evaluated dogs manifest hip issues (i.e., a greater than 50% error rate)?

Or, if a second mechanism predicts that 25% of the same population of dogs are at a higher risk, then how reliable/accurate is the second mechanism when 40% manifest hip issues?

More to the point, which of these is "more accurate"? Or, better? Is the first mechanism "better" because it predicted 100% of the manifested hip issues, even though it over-predicted the expected hip issues by a factor of 2? Or, is the second mechanism "more accurate" because it had a lower absolute error rate, even though it failed to predict 1/3 of the eventual hip issues?
 
Discussion starter · #5 ·
I think its difficult to make proper comparisons when how the image is shot can have such an impact on the score received.
There are two claims made by proponents of PennHIP.

The first is that the DI score does not significantly change with time, so a DI score for a 5-month old puppy should stay fairly constant over the life of the dog.

The second directly addresses your point about the radiography for OFAs. PennHIP proponents make the claim that the results can be reliably replicated across practitioners.