chapter 2 - major stats concepts

z-score

the number of standard deviations a value is away from the mean

normal distribution

a graph that shows a symmetrical plot around the mean and makes a "bell curve"

percentile

a number that represents a percentage of the total
"nth % of the data is less than or equal to value of nth %tile"

center

the middle of all the data (mean, median, Q1, Q3) and changes when a constant is added, subtracted, divided, or multiplied

variability

the spread of a data set (SD, range, IQR) and stays the same when a constant is added/subtracted, but changes when a constant is multiplied/divided

density curve

a probability distribution which shows the likelihood of a point having a certain value under which the area is ALWAYS 1

mean vs. median

the average of the data vs. the exact middle of all data points
equal in a normal distribution
left skewed --> median is greater, mean is smaller
right skewed --> mean is greater, median is small

68-95-99.7 rule

probability percentages in a NORMAL distribution which show

%tile interpretation

top nth percent means you need to subtract 1-n% and use inv.norm
regular %tile is regular inv. norm