Lecture 5: Descriptive Stats Flashcards
variable (noun)
an element , feature, or factor that is liable to vary or change
two types of variables
math & computing
math variable
quantity during calculation is assumed to vary
computing variable
data item that may take on more than 1 value during the run time of the program
scales of measurement: data types
- nominal
- ordinal
- continuous
nominal measurement scale
based on the classification of an observation according to the group to which it belong – a process of categorization
EX: gender, political party, marital status
ordinal measurement scale
based on the classification of an observation according to its relationship to other observations
EX: poor-fair-good scale
types of continuous measurement scales
interval & ratio
continuous interval measurement scale
equal units of measurements, distance between two numbers are known, 0 is arbitrary
uneven interval measurement scale
number used but they do NOT have to represent ‘true numbers’ that can be added/subtracted
nominal or ordinal
continuous ratio measurement scale
equal units of measurement & a TRUE 0 at its origin
EX: mass & time
population
greek symbols
constant
samples
roman characters
variable
mode
most often
best for: nominal
median
in the middle
best for: ordinal
mean
average
best for: interval/ratio
range
=X max - X min
inter-quartile range
= X 25th percentile - X 50th percentile
variance (S^2, MS)
average of square of deviations from mean divided by degrees of freedom (N-1)
standard deviation (SD)
“positive variance”
square root of variance (MS^1/2)
coefficient of variation (CV)
percentage of spread (unit-less)
=100% x (SD/mean)
central limit theorem
the sample distribution of the mean of any independent, random variable will be normal if the sample size is large enough (30-40)
conditions for more sample points
more close samples to normal distribution
conditions for less sample points
more close original population to normal distribution
