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# QQ Plot PowerPoint PPT Presentation

QQ Plot. Quantile to Quantile Plot Quantile: Points taken at regular intervals from the cumulative distribution function (CDF) of a random variable QQ Plot: Graphical method for comparing two probability distributions by plotting quantiles of their values against each other

QQ Plot

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### QQ Plot

• Quantile to Quantile Plot

• Quantile:

• Points taken at regular intervals from the cumulative distribution function (CDF) of a random variable

• QQ Plot:

• Graphical method for comparing two probability distributions by plotting quantiles of their values against each other

• Does not include spatial-temporal information

Wikipedia

### Quantiles

• If the data set have 10 values of:

• 3, 6, 7, 8, 8, 10, 13, 15, 16, 20

• 4 quantiles would result in:

• 10 x ¼ = 2.5, rounded to 3 => 7

• 10 x ½ = 5 => 8

• 10 x ¾ = 7.5, rounded to 8 => 15

### How could we do better?

• Integrate over space and time

• Use topographic surfaces as trends

### Resampling

• Bootstrapping

• Drawing sets of samples, with replacement from the original dataset

• Different results each time

• Jackknifing

• Repeat the estimation leaving out part of the dataset each time

• Repeatable

• Work with any interpolation or trend-surface method