so here in our screenplay notice first
of all that on the x-axis the component
number is plotted so this is the first
component second component third and so
on and on the y-axis we have our eigen
value plotted and in fact if you think
about it this graph is really just
plotting notice this first value three
point one three six that is right here
component two is somewhere between point
six and point seven and if you look here
here we go component two 0.63 5 notice
component three drops off just a little
it is 0.53 for component four is 0.46
three and then component five is 0.23
one so this scree plot is literally just
these eigen values plotted from left to
right
now the rule of thumb for interpreting
the scree plot is as follows what we
want to do is retain the number of
components that are above what's known
as the scree or where this plot tends to
not drop much when it tends to I
wouldn't say flat line but taper off
very gradually notice how these four
points here are these four eigenvalues
the rate of change or the slope here is
quite minimal as we move across but this
value there's a big drop from component
one to component 2 and then from
component two all the way through five
there's not much of a change anymore so
according to the scree plot we interpret
the number of components above where
they tend to not change much anymore and
where this name comes from the scree
plot scree is a geological term which
indicates the ruble or the stones that
fall from a cliff so if you think of a
cliff you're driving along a road you're
gonna see a lot of stones smaller sized
rocks than some bigger rocks but they're
all collecting along the side of the
mountain right well this is the scree or
the rubble that is collected off the
cliff so that's where this name comes
from so we want to retain the number of
components above the scree so the scree
plot would indicate to us here that we
want to retain one component suppose
there was a component right here as well
well notice that it still drops quite a
bit from here to here and then it
flatlines so if we had a component here
as well then we would retain two
components in that case but since we
only have one before the drop off then
we're just going to retain the one
component
