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Stats (CH7 Random Variables and Discrete Probability Distributions…

- - - - calculate P(X = x)
      - estimate from relative probability
  - - - indicate the direction to which the two vars tend to move
  - - - Result in only one out of two outcomes
      - The probability p of success is the same for all the trials.
      - All the trials of the experiment are independent.
      - Symmetric if p = 0.5; Skew to the right if p < 0.5; Skewed to the left if p > 0.5
      - Example
        
        Let X be the binomial random variable indicating the number of defectives.
        Define a “success” as “a converter is found to be defective”.
    - - fits cases of rare events that occur over a fixed amount of time or within a specified region
        
        number of telephone calls received by a server per hour
        
        The number of errors a typist makes per page
      - All trials experiments are independent
      - The probability of a success
        
        the same for all time intervals
        
        proportional to the length of the interval
- - - - separate into stratums first: mutually exclusive sets (strata as homogeneous groups),
    - - small-scale version of the population (i.e. heterogeneous group).
      - application: area sampling
    - - draw a sample with a size of n from N. sample one element for every N/n
  - - - Mean absolute error (MAE)
      - Root Mean Squared Error (RMSE)
        
        more sensitive to outlier as the number is squared