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• Re:"Stroke incidence and association with risk factors in women: a 32-year follow- up of The Prospective Population Study on Women in Gothenburg.
  Cecilia Bjorkelund
  Published on: 14 November 2014
• Risk factors for stroke
  Alain Braillon
  Published on: 31 October 2014

• Published on: 14 November 2014

  Re:"Stroke incidence and association with risk factors in women: a 32-year follow- up of The Prospective Population Study on Women in Gothenburg.

  • Cecilia Bjorkelund, professor, GP
  • Other Contributors:
    • Ann Blomstrand, Christian Blomstrand, Nashmil Ariai

  Answer to Comment by prof Alain Braillon

  Thank you for commenting on our paper "Stroke incidence and association with risk factors in women: a 32-year follow- up of the Prospective Population Study of Women in Gothenburg". We appreciate your proposals for extension of the paper, and in this reply, we have clarified the study design and added the inquired information.

  1. We used continuous variables i...

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  Answer to Comment by prof Alain Braillon

  Thank you for commenting on our paper "Stroke incidence and association with risk factors in women: a 32-year follow- up of the Prospective Population Study of Women in Gothenburg". We appreciate your proposals for extension of the paper, and in this reply, we have clarified the study design and added the inquired information.

  1. We used continuous variables in the analysis of baseline data except for categorical data as the ordinal data for leisure time physical inactivity, self-perceived mental stress, education where a dichotomization was used in accord with given references and data in Methods and Supporting file with references. Smoking was assessed in three categories as described. Blood pressure, blood lipids were assessed and analyzed as continuous variables. The measures were repeated as described in the original papers with references given in the "supporting file". In addition to the baseline blood pressure values analyzed as continuous variables we also used baseline diagnosis of hypertension yes/ no according to present criteria at that time. The criteria are given in Methods. To add facts in the ongoing clinical discussion about low grade hypertension we studied three levels of hypertension 1-3 at baseline in accordance to modern guidelines. We further made a model-predicted risk plot for systolic and diastolic blood pressures. Risk factors as atrial fibrillation, myocardial infarction and diabetes during follow-up were analyzed through survival curves based on Cox regression analysis. We do not agree that the title is misleading; Studying associations between baseline risk factor levels in cohort studies (e.g. Framingham, Nurse's Health Study) is an accepted epidemiological method. However, as we have the advantage of access to 4 follow-up examinations in the Prospective Population Study of Women in Gothenburg (PPSWG) during the 32 year observation period (performed 1974,1980, 1992 and 2000), we could regard it as a limitation that we have not taken full advantage of the possibility to take into account also individual changes in risk factor levels during the 32 years. However, this was not within in the aim of this study which focused on associations between baseline risk factors and stroke during follow-up.

  2. You are quite right that hazard ratio is a relative measure and gives no information about how soon stroke will occur. We have calculated median time to stroke for the women with systolic blood pressure <140 and >= 140, respectively, during the 32 years (n=105 and n=81), which was 27 (95% CI 24.17 - 26.44) and 24 (95% CI 20.50- 24.14) years (significant difference); and with diastolic blood pressure <90 and >= 90 (n=111 and n=75), which was 26 (95% CI 23.84-26.12) and 24 (95% CI 20.65-24.47) years(non-significant difference). '

  3. We have calculated population attributable fraction (PAF) for hypertension as follows:

  PAF% =100 x (NO-NE)/NT where NE= numbers expected in the exposed group if the (age standardized) risk is the same as in the control group; NO= numbers observed in the exposed group; NT= total number of cases. PAF% for SBP >140=10.91% PAF% for DBP >90=15.89%

  Thank you once again for showing interest in our paper! Ann Blomstrand, Christian Blomstrand, Nashmil Ariai, Cecilia Bjorkelund

  Conflict of Interest:

  None declared

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  Conflict of Interest:
  None declared.

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• Published on: 31 October 2014

  Risk factors for stroke

  • Alain Braillon, Consultant

  Blomstrand et al's study on stroke incidence among women and associations with risk factors deserves comments.

  First, using arbitrary cut-points for risk factors is not appropriate when there is a continuous distribution of the values with no obvious modal values. Moreover, they risk factors were based on a single assessment at baseline and there are multiple dimensions including amount and duration as well as...

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  Blomstrand et al's study on stroke incidence among women and associations with risk factors deserves comments.

  First, using arbitrary cut-points for risk factors is not appropriate when there is a continuous distribution of the values with no obvious modal values. Moreover, they risk factors were based on a single assessment at baseline and there are multiple dimensions including amount and duration as well as timing. Accordingly, the title is misleading, although the incidence study is prospective, the risk factors study is cross sectional. Breaches in such basic principles contrasts with the use of Cox proportional hazards regression models with complex adjustments and may explain why hazard ratios were low. The box "Strengths and limitations of this study" must be modified.

  Second hazard ratio is a relative measure, it tells us nothing about absolute risk and no gives us no information about how soon the stroke will occur.

  Third, Blomstrand et al should provide the population attributable fraction (PAF) which facilitates the true understanding of the contribution of a risk factor to disease burden: PAF is the proportional reduction in population disease or mortality that would occur if exposure to a risk factor were reduced to an alternative ideal exposure scenario.

  1 Blomstrand A, Blomstrand C, Ariai N, et al. Stroke incidence and association with risk factors in women: a 32-year followup of the Prospective Population Study of Women in Gothenburg. BMJ Open 2014;4:e005173.

  Conflict of Interest:

  None declared

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  Conflict of Interest:
  None declared.

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