Line graphs are useful for showing trends in quantitive data. They use a qualitative value on the y axis and can have a qualitative or quantitive value on the x axis.
When To Use a Line Graph
Use a line graph when you want to show a trend. The line between points makes it clear to viewers that there is a trend between consecutive points.
Line graphs can become really hard to read if there is a lot of data, or the trend is not very clear. In these cases, a scatter plot can be a more useful tool.
Trends can be quantified using regression or correlation. Regression is usually more useful because it shows how one variable affects the other. While correlation just indicates whether there is a relationship.
What Is The Difference Between a Line Graph and a Regression Plot
Line graphs connect each point to its next point. It does not matter if there is a big difference between the points, they will get connected.
Regression plots don't connect each point. Instead, they calculate a line of best fit and use that. The line of best fit tries to get close to as many of the data points as possible where it is allowed by the regression analysis. If the line of best fit goes through all of the data points then there may be overfitting.