Line diagrams are used to show the trend of events with the passage of time, hence incidence change ( a trend) is best depicted by a line diagram. Other options: In pie cha, areas of the segments of a circle are compared. Extremely popular but statistically inferior to bar chas. Histogram is a pictorial diagram of frequency distribution for continuous class intervals Scatter diagrams show the relationship between two objects. Eg: Positive correlation between the intakes of fat and sugar in average diets.