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Recent statistics in the relevant knowledge and learning, reading "Head First Statistics" in the process, encountered the concept of standard deviation, then understanding is not very thorough, so skip reading the following sections.
Until recently saw Yang said the teacher to explain the concept of standard deviation of PMP in the learning process, although simple, but my understanding of the standard deviation of the suddenly improved a part of it, so here I am trying to record, to consolidate a understanding, and second, to test whether they really understand the place, after all, only said that to understand, be considered really understand .
1. The standard deviation $ \ sigma $ What is the role of real life?
Basketball coach at the time to recruit players into the team, need to have a series of indicators as standard into the team; when two players physique so similar, it is difficult to choose who choose the team, this is a very poor standard time good reference;
Also, we are doing the time gap between the two players, the size of the gap can be very effective description of standard deviation.
Kobe vs 1.1 Yi
In fact, sigma standard deviation is a measure of fat or thin curve data or probability distribution.
2. Therefore, what is the standard deviation
Standard deviation data describing the degree of concentration or probability distribution. Size standard deviation, data / probabilities are not far from the expected value; on the contrary, if the large standard deviation indicates that the data / probability expectations very far away, anything can happen .
3. Q & A Q &
3.1 So, with mean not also reflect the gap between the two players do?
To take an extreme case of instability, a player playing either 60 points or 0 points, it seems to mean 30 points, and Kobe Bryant as high yet. But such a player you dare to send him to play in the finals the day it? You send him to play, he sends you to heaven.
So apparently did not reflect all the mean things I really like, you need to know is that the magnitude of change (Variance). It gives the average mean, and standard deviation are given degree of dispersion.
3.2 So, the smaller the standard deviation is always better?
Not necessarily, if you are to find out every solid player, a small standard deviation is your man; you are living or machine parts, small standard deviation then the more consistent parts.
If you prepare the entry of a new company ready to go to war, if the company is small standard deviation of wages, that you almost have a big fight or quit, you should probably find a standard deviation of big companies big fight .
3.3 standard deviation and variance What is the relationship
Standard deviation is the square of the variance. Since the statistical data with a negative sign when the standard deviation if you do not seek out the last square may be 0, so it produced a variance. Specific relationship between the two can refer to the "Head First Statistics"
3.4 Finally, the standard deviation formula
Is the root of the variance:
Wherein: x represents the data of each data set within a group, u represents the mean of these data sets, n is the number represented in the data set.
It can be simplified to:
