Measures of Central Location
The Mean
Learning Outcomes
- The sum of the numbers divided by the number of numbers.
- Also called the ‘Arithmetic Mean’ or Average
- The formula is: [latex]\bar{x} = \frac{\sum_{i=1}^{n} X_i }{n}[/latex]
Understanding Summation Notation (Σ)
- Σ means the summation (to add up all of the x terms).
- It is often used in Statistics
- Many metrics require us to sum up the values or squared values of a data set
- And it is quicker to use the ‘summation notation’ to express that sum.
EXAMPLE 1.1 — USING SUMMATION NOTATION
If the data set ‘X’ contains the following data:
x1 = 55, x2 = 62, x3 = 67, x4 = 60, x5 = 71, x6 = 66
then:
Σ xi = x1 + x2 + x3 + x4 + x5 + x6
= 55 + 62 + 67 + 60 + 71 + 66
= 381
Calculating Mean Values by Hand (Exercise)
To calculate an average (mean), we simply do the following:
- Sum up all of the values (Σ xi)
- Count the number of values in the data set (n)
- Divide the sum of all the terms by the number of data in the data set (Σ xi / n)
Knowledge Check 1.1.2
Calculating the MEAN USing Excel (Video)
We will use the average call in Excel:
- Type: ‘ = average()’
- Select all of the elements across the row or column you would like to average
- Hit enter
EXAMPLE 1.2 — USING EXCEL TO FIND AN AVERAGE
- Let us again, average out the incomes from the apartment residents,
- But this time, we will use Excel (see the video below).
- Click here to download the file shown in the video below:
Sample vs population Notation
Populations
- A population is the entire group that you want to draw conclusions about
- The population mean is indicated by the symbol μ (mu)
- Ex: All students currently registered in the BCIT School of Business make up the population
Samples
- A sample is the specific group that you will collect data from that will not include all members of the population
- The sample mean is indicated by the symbol x̄ (x-bar)
- Ex: A randomly selected group of students from BCIT whose last name begins with the letter ”B”.
Key Takeaways (exercise)
Key Takeaways: The Mean
Your Own Notes
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