# Statistical Symbols

## Statistical Symbols

Symbol | Symbol Name | Meaning |

∑ | summation | summation – sum of all values in range of series |

∑∑ | double summation | double summation |

μ | population mean | mean of population values |

E(X) | expectation value | expected value of random variable X |

E(X | Y) | conditional expectation | expected value of random variable X given Y |

var(X) | variance | variance of random variable X |

σ^{2} |
variance of population values | |

s ^{2 } |
sample variance | population samples variance estimator |

s | sample standard deviation | population samples standard deviation estimator |

std(X) | standard deviation | standard deviation of random variable X |

σ_{X} |
standard deviation | standard deviation value of random variable X |

Mo | mode | value that occurs most frequently in population |

MR | mid-range | MR = (x_{max} + x_{min}) / 2 |

Md | sample median | half the population is below this value |

Q_{1} |
lower / first quartile | 25% of population are below this value |

Q_{2} |
median / second quartile | 50% of population are below this value = median of samples |

Q3 | upper / third quartile | 75% of population are below this value |

_ X |
sample mean | average / arithmetic mean |

z_{x} |
standard score | |

X ~ | distribution of X | distribution of random variable X |

N(μ,σ^{2}) |
normal distribution | gaussian distribution |

gamma(c, λ) | gamma distribution | |

exp(λ) | exponential distribution | |

U(a,b) | uniform distribution | equal probability in range a,b |

Poisson(λ) | Poisson distribution | |