Figure 3: Interval plot for the mean arrival days for decades 1880–1950. Intervals show the 95% confidence interval for the mean decadal arrival dates. Arrival days are expressed in “day of year” and corrected for leap years; for example, “90” corresponds to March 29. The sample sizes for decades are 501 (1880s), 565 (1890s), 700 (1900s), 1126 (1910s), 1152 (1920s), 738 (1930s), 444 (1940s), 119 (1950s).