Scree plot

[1] The scree plot is used to determine the number of factors to retain in an exploratory factor analysis (FA) or principal components to keep in a principal component analysis (PCA).

According to the scree test, the "elbow" of the graph where the eigenvalues seem to level off is found and factors or components to the left of this point should be retained as significant.

Scree plots can have multiple "elbows" that make it difficult to know the correct number of factors or components to retain, making the test unreliable.

There is also no standard for the scaling of the x and y axes, which means that different statistical programs can produce different plots from the same data.

[clarification needed][1] As the "elbow" point has been defined as point of maximum curvature, as maximum curvature captures the leveling off effect operators use to identify knees, this has led to the creation of a Kneedle algorithm.