Lect. 9 Quantitative and Qualitative Predictors | Notion

Lecture Overview:

Qualitative Predictors
Interaction between variables
Some considerations in using indicator variables

Qualitative Predictors

One Factor with Two Classes

A study of the effects of childhood sexual abuse on adult females
Y: post-traumatic stress disorder (PTSD)
$X_1:$ Chldhood sexual abuse (csa); Abused or Not abused (Qualitative)
$X_2:$ The childhood physical abuse (cpa) (Quantitative)

abuse = read.table("Abuse")
head(abuse)

abuse$csa <- as.factor(abuse$csa) # Convert character into factor

class(abuse$csa)
levels(abuse$csa)

We consider the model with “csa” first
Quantitative indicators for the classes of the qualitative variable must be employed

Using Indicator Variables

There are many ways of quantitatively identifying the classes of a qualitative variable.
Let’s use 0 and 1.

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