Vocabulary of Statistics
Part 3
Data Collection - Surveys
Telephone
pros: less costly, more candid
cons: no phone, no call list
 Mailed questionnaire
pros: cover more area, less cost
cons: low response, inappropriate
responses
 Personal Interview
pros: in-depth responses,
cons: training, cost, bias

Other methods of data collection
 Observation
direct
indirect
 surveying
records
Four Methods of Sampling
 Random
 Systematic
 Stratified
 Cluster
Random
 selected
by using chance methods or
random numbers
 put
everybody’s name in a bucket and
choose
 assign a number, use a random number
generator
Systematic
 Number
each subject of the
population, then select every nth
subject.
example: 1600 kids at MHS. We
want a sample of 200.
1600 ÷ 200 = 8
Interview every 8th kid.
Stratified
 Divide
the population into groups
(called strata) according to some
characteristic that is important to the
study.
example: you might want to only
survey juniors.
Cluster
 Use
an entire, intact, group.
example: every person who lives
in a certain apartment building.
example: every person in Mrs.
Peddy’s third period class.
These are not the only methods
 convenience
sampling
- whatever is convenient to the
researcher (Wal-mart)
 sequential
 double
sampling
 multi-stage
Observational Studies
 The
researcher merely observes
what is happening or what has
happened in the past and tries to
draw conclusions based on these
observations.
Experimental Study
 The
researcher manipulates one of
the variables and tries to determine
how the manipulation influences
other variables.
teaching note: situps
 In
a true experimental study,
subjects should be assigned
randomly
 when
random assignment is not
possible (i.e. existing classrooms),
the study is said to be quasiexperimental
Independent Variable
 The
variable that is being
manipulated
 aka:
explanatory variable
Dependent Variable
 The
resultant variable.
 aka:
outcome variable.
When doing an experiment you
generally need two groups:
treatment group: the one you are
experimenting on
control group: the one you are doing
nothing to but observing
Confounding Variable
a
variable that influences the
dependent or outcome variable but
cannot by separated from the
independent variable.
Misuse of Statistics

3% of the students
of Muskogee High
School want school
uniforms.
Which one is true?

64% of the
students of
Muskogee High
School want school
uniforms.
The pure and simple truth is rarely pure
and never simple
Oscar Wilde
 First get your facts; then you can distort
them at your leisure
Mark Twain
 There are three kinds of lies: lies, damn
lies, and statistics
Benjamin Disraeli

Three out of four doctors
recommend new Zimento
Suspect Samples
 How
many doctors were actually
used?
 4?
 40?
 100?
 10,000?
 How were they chosen?
Misleading Graphs
51%
agree
49%
disagree
Misleading wording in surveys
 Do
you support bringing freedom and
democracy to the people of Iraq?
 Do
you support the unprovoked
military action of the U.S. taking
place in Iraq?
Changing values to represent the
same data
 The
incumbent states, “During my
tenure expenditures have only risen
1%.”
 The
challenger states, “During my
opponents tenure expenditures have
risen $10,000,000.”
 Both
statements are true, but one
uses percentage and the other dollar
amounts.
Detached Statistics
 Our
brand of crackers has one-third
fewer calories.
compared to what?
 Zimento
works four times faster.
faster than what?
Implied connections
 Eating
fish may help to reduce your
cholesterol.
 Studies
suggest that using Zimento
will help you reduce your weight.
 Taking
calcium will lower blood
pressure in some people.
Assignment
Page 26
1 - 29