seriograph()produces a Ford diagram highlighting the relationships between rows and columns.
eppm()computes for each cell of a numeric matrix the positive difference from the column mean percentage.
seriograph(object, ...) eppm(object, ...) # S4 method for matrix eppm(object) # S4 method for data.frame eppm(object) # S4 method for matrix seriograph(object, weights = FALSE) # S4 method for data.frame seriograph(object, weights = FALSE)
The positive difference from the column mean percentage (in french "écart positif au pourcentage moyen", EPPM) represents a deviation from the situation of statistical independence. As independence can be interpreted as the absence of relationships between types and the chronological order of the assemblages, EPPM is a useful tool to explore significance of relationship between rows and columns related to seriation (Desachy 2004).
seriograph() superimposes the frequencies (grey) and EPPM values (black)
for each row-column pair in a Ford diagram.
Desachy, B. (2004). Le sériographe EPPM: un outil informatisé de sériation graphique pour tableaux de comptages. Revue archéologique de Picardie, 3(1), 39-56. doi:10.3406/pica.2004.2396 .