A mean plot shows the mean and standard deviation of the data.
A line or dot represents the mean. A standard error or confidence interval measures uncertainty in the mean and is represented as either an error bar or diamond.
An optional error bar or band represents the standard deviation. The standard deviation gives the impression that the data is from a normal distribution centered at the mean value, with most of the data within two standard deviations of the mean. Therefore, the data should be approximately normally distributed. If the distribution is skewed, the plot is likely to mislead.