A single answer to a single opinion question does not give us a clear understanding of how people feel. However, a set of opinions can be combined to provide reliable and valid measures of belief systems.

What is a belief system? Imagine that a belief system is like our solar system. At the center is the core belief. Individual opinion statements orbit the 'star' (belief system) at the center. Unlike real stars, however, we can't actually 'see' belief systems directly. These are ideas and beliefs locked away in people's minds. They are like 'dark' stars in space. Even though we can't 'see' the stars at the center of belief systems, we can understand beliefs by looking at the opinions that are 'in the orbit' of a particular belief system. Opinions are expressions of those beliefs. Not all opinions are equal. Some are 'closer' to the core belief than others, just as Mercury is 'closer' to our Sun than Pluto.

Learn more about reliability when studying belief systems. Learn more about validity when studying belief systems.

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