2022 Introduction to Statistics in Research Mitchell 2nd ed

I N T R O T O R E S E A R C H : D A T A V I S U A L I Z A T I O N & C O M M O N S T A T T E S T S

reviewing patterns, a person can determine the best course of action (more medicine, change food choices, exercise, etc.).

In our example, using the crimes column, the range is 29.

For the student numbers at the colleges, the range is 47,301 (a difference of the highest value of 47,993 and the lowest of 692). This is quick and easy, but the disadvantage is that range only uses two values and ignores the rest.

So we need another way to consider variability and that's where standard deviation can help.

Table 66: Crime Data at colleges (FAKEData)- Repeated for convenience.)

What is interquartile range? We already talked some about quartiles when we talked about the (Q1) 25% and the (Q3) 75% quartiles. The interquartile range (IQR) describes the middle 50% of values. Essentially, the IQR is the difference between Q3 and Q1. That’s one reason box plots can be so h elpful in understanding the data since the box outlines 50% of the values.

Table 67: Interquartile Range

You now know that 50% of your data falls between 78.5 and 59.5.

What is variance? These previous examples show specific values used to understand the data, but variance combines all the values to produce a measure of spread. The variance (S 2 ) and standard deviation are the most common measures of spread. Variance is calculated by squaring deviations, so you almost need to

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