STATISTICAL CONCEPTS FOR PRECISION AGRICULTURE

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STATISTICAL CONCEPTS FOR PRECISION AGRICULTURE
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Statistics are important because ...

• Precision ag techniques generate lots of numbers.
• Management decisions are based on statistical
  descriptions.
• Inappropriate values can create unprofitable
  decisions.

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Statistical terms

• Population - all possible values of a variable.
  A dense yield map can be considered a population
  for a field.
• Sample - a selection of observations from a
  population. Ex soil samples

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Statistical terms

• Frequency distribution - the number of times a
  given value occurs in a population.
• Histogram - a graphical representation of a
  frequency distribution using classes of values.

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Two distributions with mean25
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Measures of Central Tendency
Mean
xi where n/2 values are ltx and n/2 values and gtx
Median
Mode
Xi that occurs most often
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Normal mean25, mode25, median25Uniform
mean25, modeall, median25
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Measures of dispersion
Variance
Standard Deviation
Coefficient of Variation
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Normality of Data?

• The classical measures of tendency and variance
  are based on assumptions that the data described
  are normally distributed
• In PA dataset, this is often a bad assumption

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Corn Yield in North Texas
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Parameter Relationships

• Covariance the expectation that two variables
  will vary together (e.g. percent clay and soil
  moisture)
• Correlation a measure of the strength of
  association between variables