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Chapter 4

PSYC 201W Chapter 4: Psyc 201W - Chapter 4 Notes

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A.George Alder

Chapter 4 – Defining and Measuring Variables Types of Variables • Variable – any factor or attribute that can assume two or more values o Examples  factors such as depression, externalizing behaviours, weight, and sleep habits can vary, not only across different people but also within the same person over time • Constant – a value that does NOT change o Example  mathematical constant pi (3.1416) Qualitative and Quantitative Variables • Qualitative variables – represent properties that differ in “type” (i.e., type of attribute or quality) o Examples: ▪ Sex ▪ Religious affiliation ▪ Eye colour ▪ Marital status ▪ Type of navigation error • Quantitative Variables – represent properties that differ in “amount” o Examples: ▪ Height ▪ Weight ▪ Degree of shyness ▪ Time spent learning a task ▪ Blood alcohol levels on a Saturday night • Qualitative variables, like quantitative variables, can generate numerical data and be statistically analyzed • With qualitative variables we can: o Count the number of instances that occur within each category o Report that information as frequencies, percentages, or proportions; and o Perform statistical tests Discrete and Continuous Variables • Discrete variables – between any two adjacent values (e.g., 1 or 2 or 3 children), no intermediate values are possible o Example  people might make zero, 1, 2, 3, 4, or more errors on a task, but they can’t make 1.5 or 3.789 errors • Continuous variables – in principle, between any two adjacent scale values, further intermediate values are still possible o Example  no matter how close the times are that two people take to finish a task, it is always possible for another score to exist in between o If their times are 4.0 and 5.0 seconds, then times of 4.1, 4.2, 4.3, 4.4, and so on are possible • Continuous quantitative variable appropriate to display data in line graph • Qualitative variables appropriate to display findings in bar graph Independent and Dependent Variables • Independent variable – presumed causal factor in a cause-effect relation between two variables; in an experiment, it is a factor that the researcher manipulates, or systematically varies • Dependent variable – presumed effect in a cause-effect relation between two variables; in an experiment, it is the behaviour or outcome that the researcher measures to determine whether the independent variable has produced an effect o Example  Is the speed with which people react to stimuli affected by the intensity of those stimuli? ▪ Independent variable  stimulus intensity ▪ Dependent variable  reaction time • Situational variable – characteristic that differs across environments or stimuli o Example  stimulus intensity • Subject variable – personal characteristic that differs across individuals o Example  spirituality and their degree of self-esteem • In non-experimental studies, researchers may conceptualize and discuss certain variables as if they were independent variables, but these variables are not manipulated as in an actual experiment o Example  whether religiousness and spirituality causally influence people’s physical health and longevity o For ethical and practical reasons we’re not likely to manipulate whether or how deeply people are religious o Instead we can use interviews or questionnaires to measure people’s religiousness and spirituality Constructs • Constructs – underlying, hypothetical characteristics or processes that are not directly observed but instead are inferred from measurable behaviours or outcomes o Example  Can observe you eating a huge amount of food, or observe you wolfing down food quickly, or note that you just said me, “I’m famished; time for pizza!” o Can take any of these measurable behaviours as indicators of an underlying psychological state: hunger Mediator and Moderator Variables • Mediator variable – a variable that provides a causal link in the sequence between an independent variable and a dependent variable o Example  distraction of attention occupies an intermediate position in which it is influenced by cell phone use and in turn influences driving performance • In behavioural research, mediator variables are often internal psychological constructs o Examples  distraction of attention or negative appraisals of children behaviour • Mediator variables help explain WHY an independent variable influences a dependent variable • Moderator variable – a factor that alters the strength or direction of the relation between an independent and dependent variable o Example  high traffic density vs. low traffic density and cell phone usage while driving • Moderator variables are often situational factors, but they can also be personal attributes • Moderator variables inform us about WHEN and FOR WHOM an independent variable produces a particular effect Conceptual Definitions • Scientists may disagree about how to define certain concepts or variables • Disagreement about how best to define concepts spark healthy debates and lead to new research Operational Definitions • Operational definition – defining a variable in terms of the procedures used to measure or manipulate it • In the case of constructs, operational definitions translate abstract concepts that cannot be directly observed into tangible, measurable variables o Example  In an experiment, we might operationally define stress by manipulating the environmental conditions – the situational demands – to which participants are exposed Operational Definitions in Everyday Life • Examples include: o Course syllabus o Homework handouts that describe grading criteria o Legal contracts including the lengthy “terms of use” that you typically have to agree to when downloading software or accessing services via the Internet o Job descriptions at work • People operationally define concepts in their own minds Scales of measurement • Measurement – the process of systematically assigning values (numbers, labels, or other symbols) to represent attributes of organisms, objects, or events o Systematic – values are assigned according to some rule • Scales of measurement – rules for assigning scale values to measurements o Example  for movie critics, the scale values are the number of thumbs or stars that represent the measure of “movie quality” • Although numbers can be assigned to any variable, the mathematical operations that researchers can meaningfully perform on those numbers (e.g., add, subtract, multiply, or divide them), and thus the ways in which researchers analyze and interpret their data, are influenced by the scale of
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