time. when smaller changes exist, line graphs are better to use than bar graphs. line graphs can also be used to compare changes over the same period of time for more than one group.
pie charts are best to use when you are trying to compare parts of a whole. they do not show changes over time.
bar graphs are used to compare things between different groups or to track changes over time. however, when trying to measure change over time, bar graphs are best when the changes are larger.
area graphs are very similar to line graphs. they can be used to track changes over time for one or more groups. area 