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Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/evj.12380
Letter to the Editor Dear Editor, I read with interest the paper published online by EVJ, Descriptive analysis of longitudinal endoscopy for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses training and racing at the Hong Kong Jockey Club [1], because, contrary to my more than 30 years’ racing experience, it concluded there was no difference in racing career longevity between horses that experienced EIPH and those that did not while racing without furosemide. Although the paper purportedly was peer reviewed I noticed a number of very obvious data errors and inconsistencies by the authors, Preston et al, which call into question the scientific quality of their analysis and the scientific validity of their conclusion. First, the Figure 1 pie chart (Line 418), which divides the 822 imported gelding study population into four groups (EIPH, No EIPH, Epistaxis, No endoscopy), adds up to more than 100%. To be precise it adds to 115%. The explanation by the authors of Figure 1 does not clearly reveal that the figure itself is not designed to add up to 100% as would normally be the case in a pie chart. According to the explanation of Figure 1, some of the percentages are based on total population (822 horses) and some are based on the ‘scoped’ population (732 horses). Second, in the text Preston et al state the population of 822 was narrowed to a study of 732 horses that were subjected to endoscopic examination at least once. Of that number, 405 were reported as EIPH positive and 326 were EIPH negative (Lines 151–153). Apparently one horse got lost in the mix because 405 + 326 = 731. More significantly, in Table 2 (Line 349) the authors identify 157 EIPH negative horses in Column 2 (not 326 as stated in the text [Line 153]) and 767 EIPH positive horses in Columns 2 and 3 (not 405 stated on Line 152 of the text). In the last column of Table 2 the authors report a total sample size of 924 horses (not 731 or 732 stated in the text on Lines 151, 152 and 154 and not 822 as noted on Lines 19 and 151). Which numbers, if any, are correct? Without a doubt something is seriously wrong with the accuracy of the data that groups EIPH negative and EIPH positive horses from which Preston et al. conclude (on Lines 272–274 and 293–296) there was no difference in respective career longevity between the two groups of horses. The conflicts between the text and Table 2 suggest to me the authors may have compared a group of EIPH positive horses with a mixed group of EIPH positive and negative horses. If so that certainly skews the results and probably invalidates the authors’ ‘no difference’ claim. At Line 276 the authors assert that the mean number of lifetime starts by the gelding study population was 18 compared with 16 in the USA. From that they suggest horses in Hong Kong are able to train and race successfully with EIPH and without furosemide (Line 277). But the 18 lifetime starts number is clearly wrong because as shown in Figure 2 (Line 421) it excludes three groups of geldings (EIPH negative, epistaxis, and nonendoscoped), all with fewer than 18 mean lifetime starts. Factoring in those three groups reduces mean lifetime starts for the Hong Kong horses to about 15 per horse. Even if 18 was an accurate number of starts for the Hong Kong geldings the authors’ comparison with an average of 16 starts for American horses is erroneous. The reference cited by Preston et al. in Footnote 23 (Grayson-Jockey Club Research Today, Vol. 30, No. 1) for American lifetime starts clearly states the number 16 has to be qualified because it includes not only geldings, but also nongelded horses, colts, fillies and mares that often are retired from racing for breeding purposes before their careers on
Equine Veterinary Journal •• (2015) •• © 2015 EVJ Ltd
the track would normally end. Put simply, the authors compared apples, albeit the wrong number of apples, with oranges. For that reason their conclusion about racing without furosemide does not appear to be a scientifically valid one. I also note that in responding in the Thoroughbred Daily News to some of these points raised previously by Dr Clara Fenger, Dr Riggs indicated that ‘not all horses in the study experienced the event of interest (retirement)’ i.e., the horses in this study were NOT followed for their full racing careers in Hong Kong. Additionally, there is no indication that starts for a number of these horses prior to their arrival in Hong Kong have been included in their ‘lifetime starts’ figures (34% of the imported horses had raced before importation [Line 87]). Given this circumstance, any claims presented in the Preston paper that the figures being presented are ‘lifetime starts’, as noted above, are clearly misleading and any data points in either the text, tables or figures in this paper claiming to represent ‘lifetime starts’ for these horses are clearly in error and need to be withdrawn or corrected. More specifically, if Table 2 is based on a survival analysis as Dr Riggs seems to assert, this raises some additional questions and concerns: 1) Most of the numbers in the Preston paper are contingent on the horses racing until retirement (such as lifetime starts). Nowhere in the text of the paper does it state that some of the horses did not retire. 2) If, in fact, the table represents a survival analysis, then all of the lines in the table still cannot add up to more than the number of horses in the study. They can add up to less, but not more. 3) If only the EIPH negative group had horses that did not retire, then this is meaningful all in itself: EIPH positive horses all retired, and EIPH negative horses still racing? 4) The Cox survival curves in the paper show every single curve going to zero, indicating all of the horses retiring. For this reason the authors’ conclusion about racing without furosemide does not appear to be a scientifically valid one. Finally, the ultimate quality control for any scientific paper is the ability to repeat the experiment, in this case to simply repeat and verify the data analyses. The National Horsemen’s Benevolent & Protective Association (NHBPA) therefore plans to take Dr Riggs up on his offer, contained in his Thoroughbred Daily News letter, for a ‘fair and honest debate’ by inviting the Hong Kong Jockey Club to share with the NHBPA (or a mutually agreeable organisation or individual) the data provided to the authors of this study for independent review. The NHBPA intends to make this request of Dr Riggs so that the NHBPA and the Thoroughbred breeding and racing industry may confidently revisit and re-evaluate the relevant analyses of this data set presented by Preston and her colleagues at the University of Kentucky in this very unusual e-published EVJ article. A. D. Richards President and Chairman of The National Horsemen’s Benevolent and Protective Association, Lexington, Kentucky, USA.
Reference 1. Preston, S.A., Riggs, C.M., Singleton, M.D. and Troedsson, M.H.T. (2014) Descriptive analysis of longitudinal endoscopy for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses training and racing at the Hong Kong Jockey Club. Equine Vet. J. doi:10.1111/evj.12326 [Epub ahead of print].
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Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/evj.12380
Letter to the Editor Dear Editor, I read with interest the paper published online by EVJ, Descriptive analysis of longitudinal endoscopy for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses training and racing at the Hong Kong Jockey Club [1], because, contrary to my more than 30 years’ racing experience, it concluded there was no difference in racing career longevity between horses that experienced EIPH and those that did not while racing without furosemide. Although the paper purportedly was peer reviewed I noticed a number of very obvious data errors and inconsistencies by the authors, Preston et al, which call into question the scientific quality of their analysis and the scientific validity of their conclusion. First, the Figure 1 pie chart (Line 418), which divides the 822 imported gelding study population into four groups (EIPH, No EIPH, Epistaxis, No endoscopy), adds up to more than 100%. To be precise it adds to 115%. The explanation by the authors of Figure 1 does not clearly reveal that the figure itself is not designed to add up to 100% as would normally be the case in a pie chart. According to the explanation of Figure 1, some of the percentages are based on total population (822 horses) and some are based on the ‘scoped’ population (732 horses). Second, in the text Preston et al state the population of 822 was narrowed to a study of 732 horses that were subjected to endoscopic examination at least once. Of that number, 405 were reported as EIPH positive and 326 were EIPH negative (Lines 151–153). Apparently one horse got lost in the mix because 405 + 326 = 731. More significantly, in Table 2 (Line 349) the authors identify 157 EIPH negative horses in Column 2 (not 326 as stated in the text [Line 153]) and 767 EIPH positive horses in Columns 2 and 3 (not 405 stated on Line 152 of the text). In the last column of Table 2 the authors report a total sample size of 924 horses (not 731 or 732 stated in the text on Lines 151, 152 and 154 and not 822 as noted on Lines 19 and 151). Which numbers, if any, are correct? Without a doubt something is seriously wrong with the accuracy of the data that groups EIPH negative and EIPH positive horses from which Preston et al. conclude (on Lines 272–274 and 293–296) there was no difference in respective career longevity between the two groups of horses. The conflicts between the text and Table 2 suggest to me the authors may have compared a group of EIPH positive horses with a mixed group of EIPH positive and negative horses. If so that certainly skews the results and probably invalidates the authors’ ‘no difference’ claim. At Line 276 the authors assert that the mean number of lifetime starts by the gelding study population was 18 compared with 16 in the USA. From that they suggest horses in Hong Kong are able to train and race successfully with EIPH and without furosemide (Line 277). But the 18 lifetime starts number is clearly wrong because as shown in Figure 2 (Line 421) it excludes three groups of geldings (EIPH negative, epistaxis, and nonendoscoped), all with fewer than 18 mean lifetime starts. Factoring in those three groups reduces mean lifetime starts for the Hong Kong horses to about 15 per horse. Even if 18 was an accurate number of starts for the Hong Kong geldings the authors’ comparison with an average of 16 starts for American horses is erroneous. The reference cited by Preston et al. in Footnote 23 (Grayson-Jockey Club Research Today, Vol. 30, No. 1) for American lifetime starts clearly states the number 16 has to be qualified because it includes not only geldings, but also nongelded horses, colts, fillies and mares that often are retired from racing for breeding purposes before their careers on
Equine Veterinary Journal •• (2015) •• © 2015 EVJ Ltd
the track would normally end. Put simply, the authors compared apples, albeit the wrong number of apples, with oranges. For that reason their conclusion about racing without furosemide does not appear to be a scientifically valid one. I also note that in responding in the Thoroughbred Daily News to some of these points raised previously by Dr Clara Fenger, Dr Riggs indicated that ‘not all horses in the study experienced the event of interest (retirement)’ i.e., the horses in this study were NOT followed for their full racing careers in Hong Kong. Additionally, there is no indication that starts for a number of these horses prior to their arrival in Hong Kong have been included in their ‘lifetime starts’ figures (34% of the imported horses had raced before importation [Line 87]). Given this circumstance, any claims presented in the Preston paper that the figures being presented are ‘lifetime starts’, as noted above, are clearly misleading and any data points in either the text, tables or figures in this paper claiming to represent ‘lifetime starts’ for these horses are clearly in error and need to be withdrawn or corrected. More specifically, if Table 2 is based on a survival analysis as Dr Riggs seems to assert, this raises some additional questions and concerns: 1) Most of the numbers in the Preston paper are contingent on the horses racing until retirement (such as lifetime starts). Nowhere in the text of the paper does it state that some of the horses did not retire. 2) If, in fact, the table represents a survival analysis, then all of the lines in the table still cannot add up to more than the number of horses in the study. They can add up to less, but not more. 3) If only the EIPH negative group had horses that did not retire, then this is meaningful all in itself: EIPH positive horses all retired, and EIPH negative horses still racing? 4) The Cox survival curves in the paper show every single curve going to zero, indicating all of the horses retiring. For this reason the authors’ conclusion about racing without furosemide does not appear to be a scientifically valid one. Finally, the ultimate quality control for any scientific paper is the ability to repeat the experiment, in this case to simply repeat and verify the data analyses. The National Horsemen’s Benevolent & Protective Association (NHBPA) therefore plans to take Dr Riggs up on his offer, contained in his Thoroughbred Daily News letter, for a ‘fair and honest debate’ by inviting the Hong Kong Jockey Club to share with the NHBPA (or a mutually agreeable organisation or individual) the data provided to the authors of this study for independent review. The NHBPA intends to make this request of Dr Riggs so that the NHBPA and the Thoroughbred breeding and racing industry may confidently revisit and re-evaluate the relevant analyses of this data set presented by Preston and her colleagues at the University of Kentucky in this very unusual e-published EVJ article. A. D. Richards President and Chairman of The National Horsemen’s Benevolent and Protective Association, Lexington, Kentucky, USA.
Reference 1. Preston, S.A., Riggs, C.M., Singleton, M.D. and Troedsson, M.H.T. (2014) Descriptive analysis of longitudinal endoscopy for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses training and racing at the Hong Kong Jockey Club. Equine Vet. J. doi:10.1111/evj.12326 [Epub ahead of print].
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