Variable

Definition of Variables

  • Variables: Properties or characteristics of an event, object, or person that can take on different values or amounts.

    • Contrast with Constants: Constants, such as the mathematical constant pi ($ ext{π}$), do not vary.

Examples of Variables

  • Example 1: Dogs

    • Three dogs of different breeds demonstrate various properties:

    • Height

    • Weight

    • Color

    • Length of Hair

    • Body Shape

    • Purpose for Breeding

  • Example 2: Fish

    • Fish can vary in:

    • Species

    • Shape

    • Weight

    • Type of Water (Saltwater vs. Freshwater)

Manipulating Variables in Research

  • When conducting research, experimenters often manipulate variables to test hypotheses.

    • Independent Variable: The variable manipulated by the experimenter (e.g., type of antidepressant).

    • Dependent Variable: The variable measured to assess the effect of the independent variable (e.g., level of depression).

    • Dependency: Dependent variables are sometimes referred to as dependent measures.

Identifying Variables in Research

  • Identifying independent and dependent variables is among the foremost tasks of a researcher.

    • This can be challenging for students but improves with practice.

Practice Example 1: Blueberries and Aging

  • Research Question: Can blueberries slow down aging?

  • Study Design:

    • Participants: 19 old rats (equivalent to 60-year-old humans).

    • Diets fed:

    • Standard diet

    • Supplemented with:

      • Blueberry powder

      • Strawberry powder

      • Spinach powder

    • Duration: Eight weeks

  • Dependent Variables:

    • Motor and memory tests performed afterward.

    • Findings: All supplemented rats showed improvement, but those with blueberry powder exhibited the most significant improvement.

  • Identifying Variables:

    • Independent Variable: Type of diet (rat's diet: control, blueberries, strawberries, spinach).

    • Dependent Variables: Motor and memory task performance.

Practice Example 2: Beta Carotene and Cancer

  • Research Question: Does beta carotene protect against cancer?

  • Study Design:

    • Participants: 39,000 women aged 45 and up.

    • Randomly assigned:

    • Beta carotene supplement

    • Placebo

  • Dependent Variable: Cancer rates studied over time.

  • Findings: No evidence that beta carotene affected cancer rates.

  • Identifying Variables:

    • Independent Variable: Supplement type (beta carotene vs. placebo).

    • Dependent Variable: Cancer rate.

Practice Example 3: Brake Light Brightness

  • Research Question: How bright should brake lights be to minimize stopping time?

  • Identifying Variables:

    • Independent Variable: Brightness of the brake lights.

    • Dependent Variable: Time taken for a driver to notice and react, measured in seconds.

Types of Variables

  • Qualitative Variables:

    • Express qualitative attributes without implying ordering.

    • Examples: Hair color, eye color, religion, favorite movie, gender.

    • Example from Blueberry Study: The variable "type of supplement" is qualitative (none, strawberry, blueberry, spinach).

  • Quantitative Variables:

    • Measured in numbers and imply meaningful numerical order.

    • Examples: Height, weight, shoe size.

    • Example from Blueberry Study: Memory test score is a quantitative measure of performance (measured on a scale of number correct).

  • Discrete vs. Continuous Variables:

    • Discrete Variables: Can take only specific values (e.g., number of children in a household).

    • Example: A household can have 3 or 6 children but not 4.53.

    • Continuous Variables: Can theoretically take any value within a range (e.g., time to respond).

    • Example: A response time could be 1.64 seconds or 1.64237 seconds.

    • Practicality of Measurement: Most measured variables are limited in precision, preventing them from being truly continuous.