# Chapter 5. Sensation and Perception

## 5.1Section Title

Topic: Finding the best way to describe experimental data

Statistical Concepts Covered: In this applet we will cover various measures of central tendency and how to model the relationships between data values using distributions.

Introduction

When we talk about sensation and perception, psychophysics plays a central role. Not only do we have to have accurate and reliable ways to measure stimuli and physical responses, but we must also be able to describe the results clearly and concisely. Unfortunately, there is not a one-size-fits-all solution when it comes to describing data. While you might think that talking about the average value of a data set is a reasonable approach (and often it is), the truth is that you must understand the shape of your data distribution and the point that you want to convey before you can decide on the best way to represent your data.

In this exercise, you will investigate several different data distributions and think about possible ways to describe the data. It will be helpful to you to review the text’s coverage of graphic representations and descriptive statistics (specifically mean, mode and median). Sometimes the mean value will be a fair and unbiased model of the data, but other times, the mean may misrepresent the data or even be completely uninformative. As you analyze these data and answer the related questions, you should begin to get a feel for how to select the most accurate methods for describing your findings.

Richard Alan Hullinger, Indiana University, Bloomington
Melanie Maggard, University of the Rockies

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Statistical Lesson. It may come as a surprise that more than half of the values in a distribution can be below (or above) average. You may sometimes hear friends or even professors say something like “75% of all students think that they are above average!”, implying that such a distribution is not possible. However, it is possible, and it is not even unusual. Whenever you are dealing with a skewed distribution, the mean value is pulled towards the tail and more than half of the values – sometimes far more than half of the values – can be above or below average. In fact, most Introductory Psychology classes have exam scores that are negatively skewed, so it’s quite likely that more than half of your classmates will have an above average score on the next exam!

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