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Figure 7: Box plot of endothelial cell density over the 4year followup period. On each box, the inner line is the median and the edges of the box are the 25^{th} and 75^{th} percentiles (also called first and third quartiles and indicated as q1 and q3, respectively). The whiskers extend to the most extreme data points not considered outliers, and outliers are plotted individually using a plus sign (+). The area between the first and third quartile is the interquartile range and it gives a measure of statistical dispersion of the data. The whisker length, w, has been set to 1.5, corresponding to approximately ±2.7σ and 99.3% coverage if the data are normally distributed. Points are drawn as outliers if they are larger than q3 + w(q3 – q1) or smaller than q1 – w(q3 – q1). 
