An ideographic measurement measures something in an individual without making a comparison to other people. For instance in an IQ test, my IQ score can be compared to other people. If I’m 110 and the person next to me is 140, we know who is higher in this variable. With an ideographic measurement, such as a Q-sort or repertory grip, no comparison is made. For instance, imagine there’s a list of words representing different areas of life; love, work, money, recreation, family – and the task is to place them in order of how much we agree with them, to see what importance we place on different things. We couldn’t say who was ‘highest’ – there’s nothing to be highest in.
Unlike an ideothetic measure, a nomothetic measure compares individuals against each other. Most tests and measurements fall in this group. For example, if you and I take an IQ test, we can compare our scores and see who is highest, or if we both run 100m we’ll know who is fastest.
An interval scale is similar to an ordinal scale in that the data points are ordered, however in an interval scale, the distances between these points are equal, and run on a linear scale. For instance, the distance between 5 and 10 is the same as the distance between 25 and 30, whether that’s increase in severity of symptoms, how strongly a person exhibits a personality trait, distance, etc.
Unlike a nominal scale, an ordinal scale measures a variable along an ordered scale. So if you measure something like depression on a 1 to 7 Likert scale, this is ordinal because higher numbers represent higher levels of depression.
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