Nominal:
Measurement
property.
Descriptive, no
inherent numerical
value. E.g. Gender.
Ordinal: Identity and
magnitude properties.
Values have unique
valus and an ordered
relation between
them. E.g. Results
from competition.
Interval: Identity,
magnitude and equal
intervals properties.
Know wether different
values are bigger or
smaller and how much
different they are. E.g.
Fahrenheit
50°-60°=40°-50°
Ratio: Identity,
magnitude, equal
intervals and minimum
value of 0 properties.
E.g. Weight of an
object. (All properties
together.)
Sampling methods
Non-probability
Voluntary:
People
self-select for
the survey.
(Web surveys)
Convenience:
Made up of
people easy
to reach.
Quota: A
defined sample
chosen out form
a sub-group by
the surveyer.
Probability
Systematic:
Every possible
sample of n
elements is not
equally likely.
Cluster: Clusters
are groups
randomly created
where only
individuals within
are survyed.
Stratified:
Population is
divided in strata
which are the
characteristics the
surveyer looks for.
Simple
random:With
population N and
sample n, all n
objects are equally
likely to occur.
(Lottery)
Visual displays of data
Displays:
Line graphs
Circle graphs
Bar graphs
Stem and leaf
Histogram
Frecuency distribution
Frequency:
number of times
corresponding
item occurs in
data set.
Fraction ot
percentage of
the data set
represented
by the item.
Grouped frequency
distribution: Make each
data item will fit only into
one class; make all
classes the same width;
Make sure classes do
not overlap; use from
5-12 classes.
Measures of central tendency
Median:
(n+1)/2,
ordered from
least to most.
Mode:
Value that
occurs
most often
Mean: sum of
all items
between the
number of
these.