Dear Trish Groves!
Paper - Differences in therapeutic consequences of exercise testing in a rural and an urban Danish county
Thank you very much for your letter and for giving us the opportunity to revise and resubmit the manuscript.
We would furthermore like to thank the reviewer for the constructive and pertinent comments of our study.
Enclosed a triplicate of our revised manuscript, now a "short communication", and an electronic disk version of the article.
Our response to the comments is as follows:
Reviewer N. Black:
| 1. | The authors do not make clear what their hypothesis is in the Introduction. There is a clue on page 13 when they state "we therefore expected to find the same difference in bicycle exercise test rates" as they found for coronary angiography rates. If this is their theoretical starting point, they need to consult the literature. There is a considerable amount of published evidence that distance from a service is associated with its use. Specifically in the field of CHD management I know of two - one from the US (Every NR et al. NEJM 1993; 329: 546-51) and one I published (Black N et al. JECH 1995; 49408-12). This study is therefore a confirmatory rather than an innovative contribution. It is of interest that similar findings are obtained in Denmark as have been reported from the US and UK. | |
| Ad. 1: Introduction has been changed according to the comments. Our object of the study is the relation between exercise testing and coronary angiography in a population based setting. We are puzzled about the published evidence of distance and that the study is confirmatory. We have found a few articles about accessibility, ie on-site invasive facilities or not, but no references about angiography in relation to distance and no population based references about the impact of exercise testing in the decision making of referral to angiography. The references mentioned are also about accessibility and supply factors, and not distance. In the reference of Black N et al. distance as a predictor is mentioned, but the only cited reference (nr. 16) is a congress abstract. | ||
| 2. | Methods. It was unclear (page 7 line 8) what was meant by clinicians deciding upon pre-examination waiting times. Does this mean they used an urgency rating scheme? | |
| Ad. 2: In the shortening of the article the question of waiting times has been deleted. | ||
| 3. | Results. Page 10 para 1: the variations in exercise test and angiography rates between hospital catchment areas quoted do not appear to take random variation into account. If this is true, then the authors need to use a method such as the Systematic Component of Variation to access just how much the observed differences are simply random. | |
| Ad. 3: Rate-ratios and confidence limits are calculated by epidemiological methods that do takes random variation into account, and correct for the observed number. The hospital catchment areas are only used in the linear regression model of fractions of patients with a pathological exercise test. The random variation of the fractions is not mentioned specifically, but is taken into account in the regression model by weighting by the inverse number of angiographies. | ||
| 4. | Discussion. The authors demonstrate that: | |
| (a) | levels of need (morbidity) are similar in urban and rural counties (RR 1.03) | |
| (b) | the likelihood of undergoing an exercise test is similar (RR0.96) | |
| (c) | the likelihood of an abnormal test result is similar (RR 0.88) | |
| (d) | but the likelihood of undergoing angiography differs (RR 1.40) - men 1.27, women 2.06 - and was associated with distance from the facility (b =-0.78) | |
| They offer the explanation that this was due to differences in clinical judgement (i.e.) a supply factor. For this to be true, there would have to be a systematic relationship between distance and judgement (i.e.) the further a clinician is from an angiography centre, the less likely he is to refer patients. This may be true but for economic reasons rather than cultural reasons (as suggested on page 14). In addition though, they need to consider a demand factor - that patients are less likely to want to be referred the further they have to travel. The latter is discussed on page 12 "There were no economic restrictions upon referral of patients" - maybe not to the health service but there certainly is to patients in terms of direct (travel) and indirect (loss of working time) costs. | ||
| The issue of gender differences in use of exercise tests have been investigated before. There is a new systematic review of that literature by Raine available in the October issue of J Health Services Research and Policy. The authors might want to look at it. | ||
| Ad. 4: The question about a patient barrier to referral for angiography is interesting, but due to the reduction in the original paper this is excluded. We have no data about patients willingness to undergo angiography, and do believe that this factor must be minor, because transportation to a procedure is for free and income during sick leave is guaranteed by law. Further, as mentioned on page 14, the angiography activity rose significantly during establishment of a satellite unit for coronary angiography. | ||
We hope that the paper has been revised in a manner that will make it acceptable for publication.
Yours sincerely
Troels Niemann