Elementary Statstics

5.2.3.2 False Base Line

One of the fundamental rules while constructing graphs is that the scale on the Y-axis should begin from zero. Where the lowest value to be plotted on the Y scale is relatively high and a detailed scale is required to bring out he variations in all the data, starting the Y scale with zero introduces difficulties. For example, if we have a series of production figures over a number of years ranging from 15000 units to 25000 units, then starting with a zero origin would have one of two undesirable consequences: either (i) the necessarily large intervals (say 5000 units) on the Y scale would make us lose sight of the extent of fluctuations in the curve : (ii) a necessarily large graph to permit small intervals (say 1000 units) would entail a waste of a large part of the graph, in addition to poor visual communication.

The solution is to break the Y scale : If the zero origin is the shown then the scale is broken by drawing a horizontal wavy line (also called kinked or zig-zag line) or a vertical wavy line between zero and the first unit on the Y scale which in our illustration would be 15000 units. These lines are drawn to make the reader aware of the fact that false base has been used. Three important objects of false base line are :

1. Variations in the data are clearly shown

2. A large part of the graph is not wasted or space is saved by using false base.

3. The graph provides a better visual communication.