Trend lines

# Trend lines

A trend line is a visual representation of the direction of values over a period of time. Trend lines show trends over time, by visualizing the direction of values and how fast the values change.

## Which visualizations have trend lines

Visualization Trend lines
Bar chart Yes
Line chart Yes

## When to use trend lines

A single trend line can be added to a chart to smooth out fluctuations in data, and to show any trends more clearly.

More than one trend line can be added to a chart, showing different types of trends or different values.

## Types of trend lines

### Average

An average trend line shows the average value of the data, for the time period being analyzed.

A bar chart showing sales per month. An average trend line is shown with a dashed red line.

### Linear

A linear trend line shows increase or decrease of values at a steady rate. Linear trend lines are usually used with simple linear data sets.

A bar chart showing sales per month. An linear trend line is shown with a dashed red line.

### Polynomial (second, third, fourth degree)

A polynomial trend line is a curved line used on fluctuating data.

The number of data fluctuations can determine the order of the polynomial. A second degree polynomial trend line has one hill or valley, a third degree polynomial trend line has up to two hills or valleys, and a fourth degree polynomial has up to three hills or valleys.

A bar chart showing sales per month. Polynomial trend lines of second, third, and fourth degree are shown with dashed red, yellow, and green lines respectively.

### Exponential

An exponential trend line is a curved line used when data values rise or fall at increasingly higher rates.

A bar chart showing sales per month. An exponential trend line is shown with a dashed red line.

### Logarithmic

A logarithmic trend line is a curved line used when the rate of change in data increases or decreases quickly, before leveling out.

A bar chart showing sales per month. A logarithmic trend line is shown with a dashed red line.

### Power

A power trend line is a curved line used with data sets that compare measurements that increase at specific rates.

A bar chart showing sales per month. A power trend line is shown with a dotted red line.