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Mean, Median, Mode

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Mean (Arithmetic Mean)

Definition

The arithmetic average of all values, representing the central tendency of the data.

Formula

Mean=1ni=1nxi=x1+x2+...+xnn\text{Mean} = \frac{1}{n} \sum_{i = 1}^{n} x_i = \frac{x_1 + x_2 + ... + x_n}{n}

Example

For the numbers: 2,4,6,82, 4, 6, 8

Mean=2+4+6+84=204=5\text{Mean} = \frac{2 + 4 + 6 + 8}{4} = \frac{20}{4} = 5

Key Points

  • Sensitive to extreme values (outliers)
  • Best used when data is symmetrically distributed

Comparison of Different Means

TypeFormulaExample
Arithmetic Mean1ni=1nxi=x1+x2+...+xnn\frac{1}{n}\sum_{i=1}^n x_i = \frac{x_1 + x_2 + ... + x_n}{n}2+4+6+84=5\frac{2 + 4 + 6 + 8}{4} = 5
Geometric Meani=1nxin=x1×x2×...×xnn\sqrt[n]{\prod_{i=1}^n x_i} = \sqrt[n]{x_1 \times x_2 \times ... \times x_n}2×4×6×844.4\sqrt[4]{2 \times 4 \times 6 \times 8} \approx 4.4
Harmonic Meanni=1n1xi=n1x1+1x2+...+1xn\frac{n}{\sum_{i=1}^n \frac{1}{x_i}} = \frac{n}{\frac{1}{x_1} + \frac{1}{x_2} + ... + \frac{1}{x_n}}412+14+16+183.8\frac{4}{\frac{1}{2} + \frac{1}{4} + \frac{1}{6} + \frac{1}{8}} \approx 3.8

Arithmetic Mean(Current)

Best For:
  • Simple averages of quantities
  • Calculating central tendency
  • Equal weight to all values
  • Linear relationships
Common Uses:
  • Test scores
  • Heights/weights
  • Daily temperatures
  • Income levels
Limitations:
  • Sensitive to outliers
  • Not ideal for ratios or rates

Geometric Mean

Best For:
  • Growth rates
  • Percentage changes
  • Ratios and proportions
  • Exponential relationships
Common Uses:
  • Investment returns
  • Population growth
  • Interest rates
  • Price indices
Limitations:
  • Only works with positive numbers
  • More complex calculation

Harmonic Mean

Best For:
  • Rates and speeds
  • Per-unit quantities
  • Reciprocal relationships
  • Density measurements
Common Uses:
  • Average speed over different distances
  • Price per unit calculations
  • Density measurements
  • Circuit calculations (parallel resistors)
Limitations:
  • Only works with positive numbers
  • Gives more weight to smaller values

When to Use Each Mean

Use Arithmetic Mean when you need a simple average and all values should have equal weight

Use Geometric Mean when dealing with growth rates, returns, or multiplicative changes

Use Harmonic Mean when working with rates, speeds, or other measures where using reciprocals makes sense

Median

Definition

The middle value in a sorted set of numbers. For an even number of values, it's the average of the two middle numbers.

Formula

Median={x(n+1)/2if n is oddxn/2+xn/2+12if n is even\text{Median} = \begin{cases} x_{(n+1)/2} & \text{if n is odd} \\ \frac{x_{n/2} + x_{n/2 + 1}}{2} & \text{if n is even} \end{cases}

Example

For odd number of values: 1,3,5,7,91, 3, 5, 7, 9

Median=x(n+1)/2=x(5+1)/2=x3=5\text{Median} = x_{(n+1)/2} = x_{(5+1)/2} = x_3 = 5

For even number of values: 1,3,5,71, 3, 5, 7

Median=xn/2+xn/2+12=x4/2+x4/2+12=x2+x32=3+52=4\text{Median} = \frac{x_{n/2} + x_{n/2 + 1}}{2} = \frac{x_{4/2} + x_{4/2 + 1}}{2} = \frac{x_2 + x_3}{2} = \frac{3 + 5}{2} = 4

Key Points

  • Not affected by extreme values (outliers)
  • Best used when data is skewed or contains outliers

Mode

Definition

The most frequently occurring value(s) in a set of numbers. A dataset can have no mode, one mode, or multiple modes.

Formula

Mode=value(s) with the highest frequency\text{Mode} = \text{value(s) with the highest frequency}

Example

For the numbers with multiple modes: 1,2,2,3,4,4,51, 2, 2, 3, 4, 4, 5

Mode=2,4\text{Mode} = 2, 4

Because 2 and 4 each appear twice, more than any other number

For numbers 1,2,3,41, 2, 3, 4, there is no mode because all numbers appear exactly once.

Key Points

  • Can have multiple modes (bimodal, trimodal, etc.) or no mode
  • Particularly useful for categorical data and discrete numerical data

Calculating Mean, Median, and Mode from a Bar Chart

Mean Calculation

1. Multiply each value by its frequency:

2 × 1 = 2
4 × 2 = 8
6 × 3 = 18
8 × 2 = 16
10 × 1 = 10

2. Sum all products: 2 + 8 + 18 + 16 + 10 = 54

3. Sum all frequencies: 1 + 2 + 3 + 2 + 1 = 9

4. Divide: 54 ÷ 9 = 6

Mean = 6

Median Calculation

1. List all values (including duplicates):

2, 4, 4, 6, 6, 6, 8, 8, 10

2. Find middle position: (n+1) ÷ 2 = (9+1) ÷ 2 = 5th

3. Find 5th value in ordered list

Median = 6

Mode Calculation

1. Count frequency of each value:

2: occurs 1 time
4: occurs 2 times
6: occurs 3 times
8: occurs 2 times
10: occurs 1 time

2. Find highest frequency (3)

3. Identify value(s) with that frequency

Mode = 6

Related Links

Range, Variance, Standard Deviation Calculator

Skewness Calculator

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