CENTER FOR EDUCATION STATISTICS
OFFICE OF EDUCATIONAL RESEARCH AND IMPROVEMENT 
U.S. DEPARTMENT OF EDUCATION


 

Suggestions for Use of Graphics

         
             
o simplicity is critical; cluttered graphs are ineffective. Generally no more than 7 segments in a pie graph and 4 time series in line and bar graphs should be used.    
             
o When using longitudinal data, horizontal axes intervals should be equal to time intervals.  
             
o Ordinarily, the vertical scale should start at zero. Otherwise, scale breaks should be clearly and unmistakably visible.      
             
o Vertical rather than horizontal bar graphs should be used for showing changes over time.      
             
o Stacked bar graphs, stacked area line graphs, histograms and scattergraphs are hard to read and easily misinterpreted and should be avoided.    
             
o The use of multiple pie charts to compare similar items is generally inappropriate because of the difficulty in comparing the relative sizes of wedges.  
             
o On the axes of a line graph, labels for months or years should be placed in the interval between the tick marks, but numerical values such as 1, 2, 3 should be placed on the tickmarks.
             
o In using black and white maps, areal data should contain only one variable and no more than 5, preferably 3, levels of distinction.        
             
o Because of the visual break between increments, high-low graphs, while not often used, should be considered as an alternative to line graphs when the purpose is to compare two cases of the same variable over time.