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7 – Measuring Variables

Why should I care?

The accuracy of your project depends on whether or not you are measuring the right phenomenon. The type of measurement determines what kind of tables and calculations you can generate, and also determines how far you can go when you interpret the data.

Variable:  Any aspect or characteristic that varies from case to case or over different times of observation.

Definitions      Example       Instrument
Object of Measurement

Aptitude or Ability Creativity Interview
Behaviour Physical Violence Laboratory
Level of knowledge Do you know about chemistry? Questionnaire
Opinion Wrong for psychologists to advertise? Questionnaire
Perception, Self-Perception What Churchill saw in Hitler  Content Analysis
Personal characteristic Eye Colour, Age, Skin Colour, Height Recording
Physical Trace    Kitchen Technology  Artefacts
Socio-demographic characteristic  Income Questionnaire
Type of Data

Qualitative Objects of quality, not measured by numbers. (Eye colour)
Quantitative Objects measured in quantities, using numbers. (Income)
Levels of Measurement (pp. 217-218)

Nominal   Categories. Music preference? Jazz, Rock, Classical.
Ordinal Ordered Categories. Music? Jazz 1, Rock 2, Classical 3.
Interval  Equal space scale.  From 1 – 10. Jazz 10, Rock 4, Classical 1.
Ratio Scale with absolute zero. Income scale: 0 – 10 M$

 

Why is it so useful to aim for ratio data?

Exercise

Answer the question as if you were the respondent of a survey. (You don’t have to be honest)

Then, indicate the 4 characteristics of the data, such as:

  • mutually exclusive or not
  • rank ordering or not
  • equal and measured spacing or not
  • comparing scores as ratios of each other or not

Finally, state the type of level of measurement = nominal, ordinal, interval or ratio

  1. “How many credit cards do you have?”_______6__________

_______ME______   ______RANK____   ___INTERVAL___   __RATIO_____  = __RATIO_


  1. “On average, how many packages of cigarettes do you smoke each day?” _____2____

____ME____   _____RANK__   ___INTERVAL____   ___RATIO____  = ____ RATIO ___


  1. “What languages do you speak at home?” __Cantonese, Swahili, Flemish, Congolese _

__ME_   ____   ____NO____   ___NO___    ___NO___    = ____NOMINAL____


  1. “Are you over 20 years old?” __ YES ____

___ME____   ___RANK____   ___NO SCALE___   __NO RATIO____  = ___ORDINAL___

 

  1. “What were the traffic conditions yesterday afternoon?” ___FLUID, SLOW, STOPPAGE__

____ME_____   __RANK___   __NO SCALE___   __NO RATIO____   = ___ORDINAL____


  1. “What percentage of the population earns less than $5,000 annually?” ____20 percent_______

__ME__   ___RANK__   ____ SCALE ___   ___RATIO__   = ___RATIO___


  1. “What is your gender?” (Trichotomy) ___ MALE, FEMALE, OTHER ____

__ME______   ___NO RANK ___   __NO SCALE___   ___NO RATIO___   = ____NOMINAL____

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