Title:Decisions on statin therapy by patients' opinions about survival gains: Cross sectional survey of general practitioners.

Transcription

1 Author's response to reviews Title:Decisions on statin therapy by patients' opinions about survival gains: Cross sectional survey of general practitioners. Authors: Peder Andreas Halvorsen Olaf Gjerløw Aasland Ivar Sønbø Kristiansen Version:3Date:8 April 2015 Author's response to reviews: see over

2 Dear Editor, Thank you for the opportunity to revise our paper, which is now entitled Decisions on statin therapy by patients opinions about survival gains: Cross sectional survey of general practitioners. Below we provide a point-by-point response to the thoughtful comments and suggestions from the 2 reviewers. Furthermore, we have uploaded two versions of the paper; a clean version and another with all changes marked in yellow. We believe that the paper has improved, but are happy to make further revisions if you so wish. Sincerely, Peder A. Halvorsen, MD PhD UiT the arctic university of Norway Reviewer 1 Participants: Random sample? The physicians taking part in the other survey were a random sample of Norwegian GPs. Thus we reckon that the remaining sample available for our study was also a random sample. We have clarified this on page 5, lines 5-6. Description of risk profile used in the scenario unfavorable : Thank you for pointing this out; it was a slip in language. In the scenario sent to the practitioners we stated that after 3 months the situation was virtually unchanged. On page 5 line 17 we have changed the text accordingly. Selection of survival gains The survival gains used in the scenarios to test whether GPs were sensitive patients preferences (3,6, 12m and 2,4,8yrs) were not based on discussion with patients. Our aims were to 1) cover a broad range of survival gains, 2) include the correct average survival gain of statin therapy given the patient s risk profile (6 months) and 3) limit the number of scenarios to retain power in the statistical analyses. The scale offered to practitioners for estimating the survival gain was based on informal discussions with physicians, who tended to believe that the survival gain of statin therapy must be several years, rather than several months (which was actually confirmed in our study). We have not included this information in the manuscript but are happy to do it if you so wish. Number of scenarios offered to each clinician offering more scenarios could remind GPs that patients differ Thank you for this suggestion! Since this study was part of a survey covering several other topics, we chose to have only one scenario to limit the length of the questionnaire. We now acknowledge this as a limitation in the Discussion section (page 9, lines 15 17). Discussions about the motivation for the study during the data collection period

3 We have deleted this information from the Methods and Discussion sections. Outcome measure Although our 4 point outcome measure was not field tested for this particular study, we have used similar outcome measures in several previous studies: 1: Halvorsen PA, Wisløff TF, Støvring H, Aasland O, Kristiansen IS. Therapeutic decisions by number needed to treat and survival gains: a cross-sectional survey of lipid-lowering drug recommendations. Br J Gen Pract Aug;61(589):e : Halvorsen PA, Selmer R, Kristiansen IS. Different ways to describe the benefits of risk-reducing treatments: a randomized trial. Ann Intern Med Jun 19;146(12): : Halvorsen PA, Kristiansen IS. Decisions on drug therapies by numbers needed to treat: a randomized trial. Arch Intern Med May 23;165(10): : Halvorsen PA, Kristiansen IS, Aasland OG, Førde OH. Medical doctors' perception of the "number needed to treat" (NNT). A survey of doctors' recommendations for two therapies with different NNT. Scand J Prim Health Care Sep;21(3): The reviewer rightly suggests that dichotomisation of outcome measures like ours is not generally recommended. Furthermore, we did not invite free text responses from the GPs, so dichotomisation was not justified by interpretation of data in any way. Rather, we use dichotomisation as a convenient way to present the results, so that the readers can grasp the essence of the data more easily. A sensitivity analysis showing how the odd ratios for trend presented in our table 2 would vary by choice of cutoff for the dichotomised outcome is provided below: Certainly Certainly and probably Certainly, probably and probably not Patient s required 1.00 ( ) 1.07 ( ) 1.18 ( ) survival gain 1 Physician s perception 1.72 ( ) 3.05 ( ) ( ) of survival gain 2 Physician s perception of survival gain ( ) 3.07 ( ) ( ) 1) Unadjusted odd ratios (participants randomised to different survival gains). n=1,296 2) Unadjusted odds ratios. n= 1,270 3) Adjusted for the GPs age, sex, specialty attainment and number of patients listed. n=1,217 due to missing responses. The table shows that our main finding holds regardless of how we dichotomise: The GPs response to the scenario was associated with the GPs own estimates of survival gain, but not with the patient preferences for survival gain. Alternatively, we could analyse the outcome (the GPs recommendation) as a graded 4-point outcome using ordinal regression analysis; again the GPs responses to the scenario was associated with the GPs own estimates of survival gain, but not with the patient preferences for survival gain (data not shown). However, in the analysis of the GPs perception of survival gain, the parallel lines assumption did not hold, so a partial proportional odds model would have to be fitted. The reviewer also wondered whether the impact of missing data should be explored in the analyses of GPs perception of survival gain. The table shows that the bivariate analysis, which had fewer missing

4 data, and the multivariate analysis yielded very similar odds ratios, at least for two of the cut-off points. Therefore we do not believe that our main findings could be attributed to missing data. In summary, we believe that our choice of dichotomisation conveys our main message in an easily understandable format without loss of essential information. In the Methods section (page 6, lines 14-19) we have now added the following: Although the survey provided the respondent with 4 graded response options, we dichotomized this variable when we analyzed the survey data so that certainly and probably were counted as yes, whereas probably not and certainly not were counted as no. Analysis of this variable as a 4-point response instead of as a dichotomous response yielded similar results, but for ease of understanding, we present the results with the responses grouped as described. However, we would be willing to include any of the additional analysis provided above if you so wish. It is incorrect to state that GPs own estimate of survival had greater impact on (line3, page 11) We have now deleted this sentence. Too early to make recommendation for guidelines (line 20-23, page 10) We have deleted the recommendation for authors of guidelines, which has been replaced with the following sentences: Future studies could explore whether GPs are sensitive to the patients assessment of treatment effectiveness when expressed in terms of more traditional effect measures such as absolute or relative risk reduction, or in terms of qualitative statements such as this treatment effect is good (or bad). Besides varying preferences for treatment effectiveness, patients may differ with respect to preferences regarding risk of side effects [22, 25], taking pills [22], desire to participate in decision making [25], and also with respect to the social context in which decisions are made [26]. Further insight into whether and how GPs take the patient perspective [26] into account when considering statin therapy could be important to understand enablers and barriers for shared decision making in this area. Included in this paragraph are a couple of new references to the shared decision making literature. A couple of typos Regarding cholesterol levels, both 7.5 and 7.1 are correct. The scenario provided both an initial risk profile and a new risk profile after 3 months. The figure shows the latter profile. The typo in the figure (diastolic) has been corrected. Reviewer 2 Participants: Random sample? Please see comment above. Statistically significant differences between the sample and the total population of GPs?

5 In the first paragraph of the results section (page 8, lines 4 9) we have added means, proportions and confidence intervals for the respondent characteristics, so that the readers can see statistically significant differences between the sample and the total and judge for themselves whether our sample was fairly representative: The respondents were fairly representative of Norwegian GPs with respect to age (mean 47 years, 95% CI 46 to 48), sex (36% females, CI 33 to 39) and number of patients listed (mean 1209, CI 1189 to 1229), although the total population of Norwegian GPs were slightly older (mean 49 years) and had slightly fewer patients listed (mean 1182, see table 1). The proportion with specialty attainment was somewhat higher among the respondents (66 %, CI 63 to 68) than among Norwegian GPs in general (55%). Title We have changed the title to include cross sectional survey rather than randomised trial.