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Lesson 1  Introduction to Statistical Research Methods 
Lesson 2  Visualizing Data 
Lesson 3  Central Tendency 
Lesson 4  Variability 
Lesson 5  Standardizing 
Lesson 6  Normal Distribution 
Lesson 7  Sampling Distributions 
Lesson 8  Estimation 
Lesson 9  Hypothesis Testing 
Lesson 10  tTests for Dependent Samples 
Lesson 11  tTests for Independent Samples 
Lesson 12  Intro to OneWay ANOVA 
Lesson 13  OneWay ANOVA: Test significance of differences 
Lesson 14  Correlation 
Lesson 15  Linear Regression 
Lesson 16  ChiSquared Tests 
Afterward  
Index 
Let’s say you have these two salary distributions. They have the same mean, median, and mode.
The main difference between them is the spread. One way we can see this is by looking at the range of each dataset.
The range in the top distribution is $78,600 – $21,180 = $57,420
The range in the bottom distribution is $116,020 – $7350 = $108,670
You can see from the range that the salaries of the general population are much more dispersed whereas salaries of those with social networking accounts are more concentrated.
While range is one method to describe the spread of data, it has limitations. Namely, if the data includes more people within that range, the range will not change. Take these four distributions, for example.
They all have the exact same range, and similar means, medians, and modes, but they all have very different shapes. The top left is relatively uniform; the top right is normal; the bottom left is bimodal; and the bottom right is also normal, but with more data points. Therefore, you see that the range itself does not adequately describe the spread of data.
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