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When research psychologists run a study, they collect a set of measurements as numbers.

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In cognitive psychology experiments for example

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a common measurement is the participant's’ reaction time, measured in milliseconds.

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Each participant’s reaction time is referred to as their raw score or datum, which is the singular of the word data.

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All the raw scores from the study together make up a data set.

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To understand these data and identify patterns

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researchers often arrange the data in a histogram plot from lowest to highest values.

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The histogram allows them to see at a glance how the scores are grouped

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which helps them determine the results of the study.

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However, when data sets contain hundreds or even thousands of raw scores

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psychologists calculate numbers, called descriptive statistics

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that allow them to summarize important characteristics of the distribution.

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These statistics allow us to describe the data in terms of the center of the data and the spread of the data.

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Picking the right descriptive statistic is key to interpreting data correctly.

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That is what we will examine in this activity.