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AAEC 4302 ADVANCED STATISTICAL METHODS IN AGRICULTURAL RESEARCH

AAEC 4302 ADVANCED STATISTICAL METHODS IN AGRICULTURAL RESEARCH. Chapter 7.3 Dummy Variables. Use of Dummy Variables. is the skull length (mm) of the i th mouse: X 1i sex: male or female (two categories), X 2i specie (three categories), and X 3 age. Use of Dummy Variables.

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AAEC 4302 ADVANCED STATISTICAL METHODS IN AGRICULTURAL RESEARCH

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  1. AAEC 4302ADVANCED STATISTICAL METHODS IN AGRICULTURAL RESEARCH Chapter 7.3 Dummy Variables

  2. Use of Dummy Variables • is the skull length (mm) of the ith mouse: • X1i sex: male or female (two categories), • X2i specie (three categories), and • X3 age.

  3. Use of Dummy Variables Model to estimate: Estimated Model:

  4. Use of Dummy Variables • For a male mouse of the first specie: 1 1 0 D11: 1 if sex = Male, 0 otherwise D21: 1 if species = 1, 0 otherwise D22: 1 if species = 2, 0 otherwise

  5. Use of Dummy Variables • For a male mouse of the second specie: 1 0 1 D11: 1 if sex = Male, 0 otherwise D21: 1 if species = 1, 0 otherwise D22: 1 if species = 2, 0 otherwise

  6. Use of Dummy Variables • For a male mouse of the third specie: 1 0 0 D11: 1 if sex = Male, 0 otherwise D21: 1 if species = 1, 0 otherwise D22: 1 if species = 2, 0 otherwise

  7. Use of Dummy Variables • For a female mouse of the first specie: 0 1 0 D11: 1 if sex = Male, 0 otherwise D21: 1 if species = 1, 0 otherwise D22: 1 if species = 2, 0 otherwise

  8. Use of Dummy Variables • For a female mouse of the second specie: 0 0 1 D11: 1 if sex = Male, 0 otherwise D21: 1 if species = 1, 0 otherwise D22: 1 if species = 2, 0 otherwise

  9. Use of Dummy Variables • For a female mouse of the third specie: 0 0 0 D11: 1 if sex = Male, 0 otherwise D21: 1 if species = 1, 0 otherwise D22: 1 if species = 2, 0 otherwise

  10. Use of Dummy Variables • measures the skull length for a female mouse of specie 3 at birth, i.e. age = 0 • : The skull length for a female mouse of specie 3 at birth is 33 mm.

  11. Use of Dummy Variables • measures the difference in skull length (for any age) between male and female for any specie • : means that regardless of age, a male mouse will have a skull length 3.05 mm larger than a female mouse

  12. Use of Dummy Variables • measures the difference in skull length (for male mouse of any age) between species one and three • : means that a mouse of species 1 will have a skull length 4.9 mm smaller than a mouse of species 3, regardless of sex and age.

  13. Use of Dummy Variables • measures the difference in skull length (male or female mice of any age) between species two and three • : means that a mouse of species 2 will have a skull length 0.22 mm smaller than a mouse of species 3, regardless of sex and age.

  14. Use of Dummy Variables • measures the difference in skull length (for male or female mice of any age) between species one and two • (-4.9) – (-0.22) = -4.68 means the skull length for species 1 is 4.68 mm shorter than for species 2, regardless of age and sex.

  15. Use of Dummy Variables • Dummy variables in models are often called “intercept shifters”

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