Stacked area charts work great when charting raw values, averages, counts, and percentage of total. The sum of the values across the different groups will add up to that of the entire set.
But what about in the case when the value being charted is a Median, Geo Mean, or any Percentile? In these cases the sum of the values (say Media) across the categories will not add up to the Median value of the entire set.
Example: We have the data on the consumption of Meat, Vegetables, Fruits, and Dairy for a country. For each category (and the entire set) we have the median pounds consumed per person, each year, for the last 10 years. If we were to draw them in a stacked area chart, the sum of the values for a given year would not equal the median pounds consumed per person across all the categories.
Is it fair to assume that the stacked charts should be avoided in these cases as they will cause confusion?