Chap 3: Numerical descriptive measures Flashcards
central tendency?
numerical variables are grouped around a typical, central value
Ex: mean, median, mode
variation?
show the amount of dispersion, scattering away from a central value
Ex: range, variance, Std dev, coefficient of variance, Z-score
shape?
the pattern of the distribution
from lowest -> highest
Ex: skewness & Kurtosis
the mean?
= balance point
median?
middle value in an ordered array of data ranked from smallest -> largest
= (n+1)/2 ranked value
Ex: median num of calories = 110 —> half of breakfast cereals have equal or less than 110 calories
rules to determine median?
- odd num of values -> median = middle ranked value
2. even num of values -> average of the two middle-ranked values
mode?
values appear most frequently
range
= diff btw largest n smallest value
= total spread of data
variance n Std Dev
how large values fluctuate above/below the mean
never be negative
Ex: Std Dev = 46.09 —> the calories are clustering within +/- 46.09 around the mean 15.
coefficient of variation
- measures the scatter of data relative to mean
- always in %
- useful when comparing 2 data sets
Z scores
help identify outliers
> 3 and outlier
skewness?
measure the extent to which data values are not symmetrical around the mean
perfectly symmetrical?
skewness = 0
mean
negative, left skewed distribution
mean = median
symmetrical distribution w zero skewness
