Vector plots of raw data with various summary statistics. The base of the arrows (closed circles) are the number of taps (x-axis) and UHDRS scores (y-axis) upon entry into the study (A). The tip of the arrows represent the number of taps and UHDRS scores several years later. For example, the orange patient could perform 85 taps initially, but only 40 at the final assessment (compare with Fig 1A), whereas this patient had an initial UHDRS score of approximately 40 and a final score of 50 (compare with Fig 1B). The length of the arrow has a straightforward interpretation: the longer the arrow the greater the disease progression, and with this dataset arrows pointing up and to the left indicate disease progression. The black arrow is the mean vector, and thus offers a visual summary of the raw data. In graph (B) the initial values are highlighted by plotting them in a different colour, and instead of a mean vector, the mean of the initial (blue circles) and final (red diamonds) values are shown on the axes. The ellipses are the 2D interquartile range of the initial (blue) and final (red) values. In graph (C) the axes show the range of the data for both initial and final values and convex polygons enclose the initial (blue) and final (red) values, which allows easier visual separation of the data at both time points.