Chapter 3- Defining and Measuring Variables Flashcards
Variable
any characteristic of a person, non-human subject (rat), situation, environment, or research condition that can vary or change. If we are talking about variables that have to do with people, we may study characteristics that vary within a person at different times (mood, exercise) or characteristics that vary between people (personality, demographic characteristics).
hypothetical construct
A hypothetical characteristic or mechanism that helps explain and predict behaviour or attitudes. Typically, these characteristics or mechanisms are not directly observable, but we know (or believe) they are there
operational definition
specifies a procedure (exact steps) for measuring or manipulating a construct or variable. As with construct definitions, we can (should!) consult the literature for “established” methods if these exist! It is generally fine (and encouraged) to use measures (or manipulations) of constructs created by other researchers so long as we properly cite them.
reliability
refers to how consistent or stable our measurements are.
validity
unlike reliability, evaluates whether or not we are actually measuring what we claim we are.
correlation coefficient (r)
(usually denoted by the letter r) looks at the strength of a relationship between two variables. The correlation can range in value from -1 to + 1. It has two components:
Correlations have a strength –The closer the value is to 1 (it doesn’t matter if it is positive or negative.), the stronger the relationship between the variables.
Correlations also have a direction;
negative correlation
(e.g., -0.8) means that as one variable increases, the other decreases. So, you might see a negative correlation between students’ study time and stress during a test– the more hours you put in studying, the less stress you will experience on test day.
positive correlation
(e.g., +0.8) means that as one variable increases, so does the other. So, you might see a positive correlation between time spent studying and grades– as time spent studying increases, grades also increase.
Combining these, then, r=:0 = no relationship,1 = strong positive relationship, -1 = strong negative relationship
test-retest reliability
established by comparing the scores obtained from two successive measurements of the same individuals and calculating a correlation between the two sets of scores. If alternative versions of the measuring instrument are used for the two measurements, the reliability measure is called parallel-forms reliability.
inter-rater reliability
the degree of agreement between two observers who simultaneously record measurements of the behaviours.
split-half reliability
obtained by splitting the items on a questionnaire or test in half, computing a separate score for each half, and then calculating the degree of consistency between the two scores for a group of participants.
scale of measurement
The set of categories used for the classification of individuals. The four types of measurement scales are nominal, ordinal, interval, and ratio.
nominal scale
A scale of measurement in which the categories represent qualitative differences in the variable being measured. The categories have different names but are not related to each other in any systematic way.
ordinal scale
A scale of measurement on which the categories have different names and are organized sequentially (for example, first, second, third).
interval
A scale of measurement in which the categories are organized sequentially and all categories are the same size. The zero point of an interval scale is arbitrary and does not indicate a total absence of the variable being measured.
