RELATIONSHIP BETWEEN TWO NUMERICAL VARIABLES

By Farrokh Alemi, Ph.D.

Investigators are often interested in relationship between variables

Relationships

Multiple observations needed

Anecdotal Data

I have smoked all my life and I do not have cancer

Anecdotal Data

Relationships

Independent X & Y

Explanatory Variable𝐸𝑥𝑝𝑙𝑎𝑛𝑎𝑡𝑜𝑟𝑦 𝑣𝑎𝑟𝑖𝑎𝑏𝑙𝑒 𝑚𝑖𝑔ℎ𝑡 𝑎𝑓𝑓𝑒𝑐𝑡

ሱۛ ۛ ۛ ۛ ۛ ۛ ۛ ۛ ሮ 𝑅𝑒𝑠𝑝𝑜𝑛𝑠𝑒

Association Is Not Causation

Causation Requires: Association Sequence (causes preceded effects) Mechanism Counter factual (no effect when causes

are absent)

Causation Requires: Association Sequence (causes preceded effects) Mechanism Counter factual (no effect when causes

are absent)

Causation Requires: Association Sequence (causes preceded effects) Mechanism Counter factual (no effect when causes

are absent)

Causation Requires: Association Sequence (causes preceded effects) Mechanism Counter factual (no effect when causes

are absent)

Association Is Not Causation

A Scatterplot can show the association between two variables

Take Home Message

Do one: