5.3 Identification

Identification: finding and isolating part of variation that answers research question

Example of Family Dog, Rex, Escaping House

• Rex escapes house each night while owners sleep

• One of the owners, Annie, believes dog is escaping through basement window

• The owners close-off possible causes of escape in sequential evenings:

  • doggie door
    
  • back door, doggie door
  • blinds, back door, doggie door
    
  • air vent, blinds, back door, doggie door
  • Additional cumulative steps taken (e.g., closing off chimney)

• Rex still escapes each night after owners address potential causes

• Only remaining escape hatch is basement window

Identification Process

Broad overview

• Research question takes us from theory to hypothesis
  
• Identification takes us from hypothesis to data

Identification in Dog Example

• Hypothesis: Rex escapes through basement window
• Testing hypothesis involves removing alternative explanations, and isolating the basement window as the single cause of escape.

Identification in Practice

• Use statistical procedures to remove unwanted sources of variation
  
• Still need theory and assumptions about DGP

Steps to answer research question:

• Use theory to describe DGP
  
• Use DGP to to find reasons why data appear a certain way that doesn’t address research question
  
• Block alternate reasons to isolate variation of interest