Definition

1
Definition Measurement
measurement is the beginning of science, until
you can measure something, your knowledge is
meager and unsatisfactory Lord Kelvin
Nominal/Conceptual Definition - define concept in
terms of other concepts, links concepts without
tying them to real world Operational definition -
equates definition with measurement, specify
procedures/operations to generate the concept.
2
EXAMPLE 1. CONCEPTUAL DEFINITION - Length of
table is the distance from one end to the other.
OPERATIONAL DEFINITION - Place a yardstick
along one edge of the table, place additional
yardsticks end to end until one extends over the
other edge. Read the numeric marking for inches
on the final yardstick at the point where it is
exactly over the other edge of the table (call
this X inches). Count the number of yardsticks
you have used (call this N). Compute (N-1) 36
X. Repeat this process on the edge perpendicular
to this one. The length of the table in inches is
the larger of these two numbers.
3
EXAMPLE 2. CONCEPTUAL DEFINITION - Age- the
number of years that have passed since a person's
date of birth. OPERATIONAL DEFINITION - A.
Ask an individual for his name, place of birth
(county and state), and names of both parents. Go
to the county records office for the given county
and find the record for the person with the given
name. If there are more than one such records,
check for names of parents. Identify the date of
birth from this record. Subtract the year of
birth from 1998. If the month and day of birth
has not yet been reached in the current year,
subtract 1.
4
AGE Operational Definition B Give the subject
a slip of paper with the following
question. ENTER YOUR AGE IN YEARS AT YOUR LAST
BIRTHDAY ______. The number written in the
blank is the person's age.
5
Levels of Measurement
Nominal - unordered categories,
race Ordinal - ordered categories,
sm, med, lg Interval - consistent distance
between levels Temperature
Fahrenheit Ratio - natural zero Temperature
Kelvin
6
Levels of Measurement
7
Examples of Measurement scales- Income
NOMINAL Middle income if income is between 30K
and 50K Not middle if less than 30K or more
than 50K. ORDINAL LOW is less than 30K MID
if between 30K and 50K HIGH if greater than
50K INTERVAL Income in dollars from Line 17 of
1997 tax return. RATIO Income in dollars
10,000.
8
Reliability and Validity of Measures
RELIABILITY Absence of random error (noise),
refers to repeatability of the measure. Do we get
same answer each time we make measurement? Inter-
rater, test-retest, split half, parallel forms,
Internal consistency- Cronbachs alpha,
KR VALIDITY Absence of systematic error
(bias). Are we measuring what we purport to be
measuring? Content validity (Trochim-
Translation validity) Criterion-related
validity predictive, concurent, convergent,
discriminant Construct validity MTMM
9
Validity vs Reliability
10
Statistics measurement level
A dichotomous variable (0 or 1) can be treated as
interval
11
Assessing Reliability

• Inter-rater reliability
• Test-retest
• Alternative forms
• Internal consistency
• Inter-item correlations
• Split half
• Cronbach's alpha

12
Types of Validity

• Translation validity (face, content)
• Criterion-related validity check against other
  criteria
• Predictive validity can predict
• Concurrent validity distinguish groups
• Convergent validity- correlates with similar
  measures
• Discriminant validity neg correlation with
  dissimilar measures