Describing a Simple plot of Data
When you examine a plot of data, you should:
- First, look ar the abcissa (horizontal) value, and try to
determine what it means. Is it time? If so, does time flow
from left to right or right to left? Is it vertical (or horizontal)
distance on the earth? If so, which way is up (or north or east).
Examine the units, too, to get a feel for the amount of time or
distance (or whatever) that is being graphed.
- Second look at the overall range of variation of the
ordinate (vertical) value. What does it represent, physically?
Is its range small or large, compared to the typical values? A curve
that varies between 0 and 100 is probably telling you something
different than one that varies between 99.999 and 100!
- Third, look at the shape of the curve:
--Does the ordinate increase or decrease consistently with
increasing abcissa value? If so, the curve is said to 'monotonically'
increase or decrease. Even if it is somewhat variable, if there a general
trend? Does it mostly increase or decrease with increasing abcissa value?
--Does the curve have a series of peaks? If so, how many peaks occur?
How wide are they, and how wide is the space between them? A curve might
have sharp peaks separated by flat intervals, or broad peaks.
--Does the curve have any sharp steps or jumps. If so, how
many? How much does the ordinate change across the steps?
--Does the overall appearance of the curve remind you of anything:
a straight line, a bell curve, waves on the ocean; a staircase; a sawtooth pattern; scallops, etc.?