what is the purpose of standard deviation?
quantified the spread of data around the mean
how would you calculate standard deviation?
- find mean
- find square of each data point’s distance to the mean
- sum values so far
- divide by number of data points
- square root
what is the standard error?
spread of sample means
what are the differences between standard deviation and standard error?
SD - measures spread around mean for this population
SE - measures spread of several means from various populations and estimates how far away from sample mean the true mean is
SD - describes spread around mean
SE - estimates real mean
normal distribution:
how much of the data is within 1 standard deviation of the mean?
68%
normal distribution:
how much of the data is within 2 standard deviations of the mean?
95%
normal distribution:
how much of the data is within 3 standard deviations of the mean?
99.7%
what is a negative skew of data?
peak to the right
what is a positive skew of data?
peak to the left
what is a vertical skew of data?
peak in the middle, but not normally distributed
what is the IQR?
measure of spread
how would you calculate the IQR?
UQ - LQ
when is the IQR used?
- when data is not normally distributed
- alongside median
what are confidence intervals?
range of values our population mean is likely to lie in
what does a 95% confidence interval mean?
there is a 95% chance the mean lies within the interval
- confidently limits the parameter
how would you calculate a 95% confidence interval?
mean +/- (1.96 x SE)
mean +/- (1.96 x SD/root n)
what are histograms?
- continuous box plots
- representing bars cover a range
what are box and whisker plots?
compare continuous variable between multiple groups
what are scatterplots?
display 2 continuous variables
