Non-continuous variables 08B

Non-continuous variables 08B - 1 Regression with...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 Regression with categorical independent variables ESM 206B 15 Jan. 2008 2 Types of variables Numeric Continuous Observations can take on, in principle, any real number Infinite # of possible values between 1 and 10 Discrete Observations can take on, in principle, any integer 10 possible values between 1 and 10 Categorical Dichotomous: Male/Female Pre-regulation/Post-regulation Island/Mainland Nominal (nom = named) Continent Political party Soil type Ordinal (ord = ordered) Survey response: strongly disagree, disagree, neutral, agree, strongly agree Size classifications: small, medium, large Income ranges 3 Dummy variables How can we handle categorical explanatory (independent) variables in a regression? Answer: make a dummy! Dichotomous: zero or one Categorical with q categories: q-1variables each scored zero or one (examples to follow) 4 Alien Species Exotic species cause economic and ecological damage Not all countries equally invaded Want to understand characteristics of country that make it more likely to be invaded. Well measure invasiveness as fraction of species that are Alien Two hypotheses 1. Human population density plays a role in a countrys invasiveness. 2. Island nations are more invaded than mainland nations. 5 200 400 600 800 1000 1200 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Pop_dens Prop_exotic Mainland Island 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Island Prop_exotic 6 A Simple Model ISL is a Dummy variable , coded 0 if mainland, 1 if island Dummy changes intercept (explain). i i i i P ISL A + + + = 3 2 1 7 Call: lm(formula = Prop_exotic ~ Pop_dens + Island, data = ExoticSpecies) Coefficients: Estimate Std. Error t value Pr(>|t|) (Intercept) 7.944e-02 2.708e-02 2.934 2....
View Full Document

Page1 / 24

Non-continuous variables 08B - 1 Regression with...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online