Reply to letter to editor regarding: Correlation between uterine artery Doppler indices and menstrual irregularities among levonorgestrel-releasing intrauterine system and depot medroxyprogesterone acetate users: a prospective observational study

Response to letter to editor entitled ‘Uterine artery Doppler among hormonal long acting reversible contraceptive methods users: Statistical concerns’ [1]. It’s our pleasure to see the interest of some readers in our published research work [2]. Indeed, our observational study was based on previous studies’ reports which were conducted on a smaller number of participants such as what reported by Pakarinen et al. [3] who enrolled 10 women, Bastianelli et al., [4] who conducted a longitudinal study on 32 women and lastly the study by Hussein [5] which was conducted on 40 women. Our sample size (206 women) was far larger than all of them. In fact, we did not measure the correlation statistically, but it was intuitively ‘indirectly’ inferred according to statistically significant differences between menstrual irregularities and Doppler indices when compared to the baseline Doppler indices. For that reason in our conclusion, we added the phrase; larger multicentre studies are warranted to potentiate our findings. It is a commonly held misapprehension that for normally distributed data one uses the mean, and for non-normally distributed data one uses the median. Albeit the use of the median and interquartile range is advised for presentation of abnormal data distribution in some areas of the statistical literature, the use of both the mean and the standard deviation cannot absolutely be denied. If the data are not normally distributed, the mean still can give useful information [6]. Three factors drive the statistical significance, namely the amount of study data (sample size), the differences between the mean study variables and the standard deviation of the differences. Concerning the statistically significant relationships presented in the results; the difference between the mean values of the uterine artery resistance index (RI) after 6 months and 3 years in the study groups was 0.01 and the same figure is also found considering the difference between their related standard deviations but because of a relatively large sample size, p value was less than . 05 in both conditions. The fair amount of data (large sample size) can yield significant statistical significance in spite of small differences of the means or their standard deviations. This concept also applies to the significant statistical difference in the mean values of RI in study groups at two and three years for from the initial RI. In women with heavy bleeding, the mean values of the pulsatility index (PI) in study groups did not differ statistically to a significant level as ‘p’ value was > . 5. Indeed, the probability value (p) mentioned by our dear reader was the outcome result value of Mann–Whitney test which mistakenly thought of him as ‘p’ value. It seemed that the underlying presence of outliers’ data variables together with some abnormal data distribution may have led to slightly higher mean value of (PI) in women with abnormal bleeding than those with either spotting or heavy bleeding. Inquiry about adverse effects was done at each scheduled visit with an appropriate undertaking management of symptoms. Accurate evaluation of the symptoms was done to verify their affiliation to the used method. Of course patients adverse effects were thoroughly managed and these symptoms did not affect the overall satisfaction as in a previous study by Lessard et al. [7] who conducted a 7-year follow up study of 187 women who had an LNG-IUS inserted for contraception and reported a high frequency of candidiasis among participants from the 4th through the 7th year of use in comparison to the first year without request for method withdrawal.