fixed a typo in caption fig 9.1

boxplots_violins.Rmd

@@ -17,7 +17,7 @@ Whenever we are dealing with many distributions, it is helpful to think in terms
 
 The simplest approach to showing many distributions at once is to show their mean or median as points, with some indication of the variation around the mean or median shown by error bars. Figure \@ref(fig:lincoln-temp-points-errorbars) demonstrates this approach for the distributions of monthly temperatures in Lincoln, Nebraska, in 2016. I have labeled this figure as bad because there are multiple problems with this approach. First, by representing each distribution by only one point and two error bars, we are losing a lot of information about the data. Second, it is not immediately obvious what the points represent, even though most readers would likely guess that they represent either the mean or the median. Third, it is definitely not obvious what the error bars represent. Do they represent the standard deviation of the data, the standard error of the mean, a 95% confidence interval, or something else altogether? There is no commonly accepted standard. By reading the figure caption of Figure \@ref(fig:lincoln-temp-points-errorbars), we can see that they represent here twice the standard deviation of the daily mean temperatures, meant to indicate the range that contains approximately 95% of the data. However, error bars are more commonly employed to visualize the standard error (or twice the standard error for a 95% confidence interval), and it is easy for readers to confuse the standard error with the standard deviation. The standard error quantifies how accurate our estimate of the mean is, whereas the standard deviation estimates how much spread there is in the data around the mean. It is possible for a dataset to have both a very small standard error of the mean and a very large standard deviation. Fourth, symmetric error bars are misleading if there is any skew in the data, which is the case here and almost always for real-world datasets.
 
-(ref:lincoln-temp-points-errorbars) Mean daily temperatures in Lincoln, Nebraska in 2016. Points represent the average daily mean temperatures for each month, averaged over all days of the month, and error bars represent twice the standard deviation of the daily mean temperatures within each month. This figure has been labeled as "bad" because because error bars are conventionally used to visualize the uncertainty of an estimate, not the variability in a population. Data source: Weather Underground
+(ref:lincoln-temp-points-errorbars) Mean daily temperatures in Lincoln, Nebraska in 2016. Points represent the average daily mean temperatures for each month, averaged over all days of the month, and error bars represent twice the standard deviation of the daily mean temperatures within each month. This figure has been labeled as "bad" because error bars are conventionally used to visualize the uncertainty of an estimate, not the variability in a population. Data source: Weather Underground
 
 ```{r lincoln-temp-points-errorbars, fig.cap = '(ref:lincoln-temp-points-errorbars)'}
 lincoln_weather %>%