6.5.7 Graphics

As in principal components analysis, the results of correspondence analysis are presented on graphs that represent the configurations of points in projection planes, formed by the first principal axes taken two at a time. It is customary to summarize the row and column coordinates in a single plot. However, it is important to remember that in such plots, one can only interpret the distances between row points, and the distances between column points, but not the distances between row points and column points. However, it is legitimate to interpret the relative positions of one point of one set with respect to all the points of the other set

The joint display of row and column points shows the relation between a point from one set and all points of another set, not between individual points between each set. Except in special cases, it is extremely dangerous to interpret the proximity of two points corresponding to different sets of points.

Some keys for interpreting the factorial maps are:

• Points near the origin have undifferentiated profile distribution as a consequence of the origin being placed at the center of gravity of both clouds N ( I ) and N ( J ).
• The points, which do not contribute essentially to the inertia of each axis, are virtually identical to the average profile.
• Points of a cloud (or set) situated away from the origin, but close to each other have similar profiles
• Geometrically, a particular row profile would be attracted to a position in its subspace, that corresponds to column variable categories prominent in that row profile.
• When correspondence analysis has more than two dimensions. Proximity with one pair of axes may disappear when other axes are (added) plotted.
• It is customary to summarize the row and column coordinates in a single plot. However, it is important to remember that in such plots, one can only interpret the distances between row points, and the distances between column points, but not the distances between row points and column points. cannot be interpreted. The joint display of coordinates shows the relation between a point from one set and all points of the other set and not between individual points between each set.
• A point makes a high contribution to the inertia of a principal axis in two ways –when it has a large distance from the barycenter, even if it has a small mass, or when it has a large mass, but a small distance. Considering all these points, it is necessary that the numerical results of correspondence analysis, viz. mass. Absolute contribution (CTR) and relative contribution COS² j are all taken into account for interpreting the results of correspondence analysis.