What Does the Mean Mean?
نویسندگان
چکیده
As the Internet has become a big business, its performance has become an important question. Several companies have started monitoring Internet performance, many ISPs now conduct internal performance measurements, and there are also independent organizations such as RIPE that conduct regular performance monitoring of ISPs. The exact form of measurements may vary, but typically they are based on active probing. A common result presented is an overall statistic combining the measurements over a whole network, and this is frequently used to rate, or rank ISP performance, and is sometimes used as a metric for overall network health. Of course, a single number cannot hope to validly represent all of the information gathered in these types of measurements, but nevertheless, this type of measure is used, and we should ensure that the methodology for compiling the measurements is robust, and appropriate. Most methods that have been used are based on the mean, but it is surprising how diverse the “mean” can be. There are several alternatives (e.g. arithmetic mean versus geometric mean), and each company applying these methods seems to use a different approach. This paper considers five approaches in detail and, explains which of these is the best, and why. In particular, we show that the geometric, and harmonic means, while appealing because of their robustness to outliers, are actually very poor statistics to use when combining Internet measurements, and can cause changes in apparent performance without any real change in the network performance.
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