1
Levels of Measurement
Evaluation and Measurements By
Isabelle Devreux
2
Objectives of the Lecture
Define and explain the different types of levels of measurements:
Nominal,
Ordinal,
Interval
Ratio level of measurement.
To be able to differentiate and specify the caracteristics of the 4 various levels of measurement.
To know the limitations of each measurement level
3
Levels of Measurements
Physiotherapists deal with measurements ( limb length, muscle strength, ROM, sensation,..).
Levels of measurements are categorized for measuring variables and know if changing with the time or type of treatment.
From the least to the most sensitive, the scales are:
nominal,
ordinal,
interval and
ratio.
-Name
-Order, rank -Period, group -In comparison
4
1) Nominal level of measurements:
It is used to classify or categorize data.
It does not imply any type of magnitude but simply category, so they can not be ordered or added.
A clinical example would be arthritis. Arthritic patients could be categorized into patients with osteoarthritis, rheumatoid arthritis and traumatic arthritis. The
differentiation is simply according to the type of disease.
Nominal level takes place in all of subcategories.
I.e: Per disease, or per alphabetical order, or per types of reflexes, per type of cardiopathies ,per nationality, per types of fractures of the lower limb…
5
Examples of nominal type of measurement
Types of
nationalities
attending PT with acertain
pathology:
Saudis yes
Gulf yes
Egypt yes
Jordan No
Yemen No
Types of arthritis cases in PT dept:
Osteo-arthritis +
Traumatic Arthritis -
Rheumatoid arthritis
+ Orthopedics
Pathologies of LL benefiting of coldpacks
Osteoartritis of knee
P
Fractures of femur P
Total hip replacement P
Only 2 choices are possible : present or absent, dead or alive, yes or no, 1 or 2
6
Nominal levels of measurement:
Types of
technical aids used for
ambulation in hemiplegia
Wheelchair
No
Rollator
No
Quadripod stick
Yes
Cane
Yes
Stick
Yes
Types of
neurological symptoms of Pain
Left
cervical spine pain P
Right cervical spine pain A
Right head ache A
Left arm pain
P
Left hand parastesia
P
7
2) Ordinal level of measurements:
In this level, magnitude (or importance)is added for categorization.
Ordinal numbers indicate more than rank order of the objects.
The numbers do not imply definite magnitude, nor they imply that the categories are the same, in terms of the quantity that they represent.
It does not imply that the intervals between the numbers are equal.
The values of ordinal measurements can be summarized by frequency of occurrence, by percentage of the whole or by counting the members in the category.
8
EX: Number of patients in the clinic of orthopedic rehabilitation per month:
Had Muscle strength grading:
Grade 4 10 patients or 10%
Grade 3 20 patients or 20%
Grade 2 50 patients or 50%
Grade 1& 0 20 patients or 20%
Had screening for Hypertension before therapy:
Diastolic BP
140 and above 10
120 – 140 40
100 - 120 20
100 and below 5
Grading of how many steps the patient can achieve without assistance after 1 day, 1 week,2weeks,…
Gives frequence, a %Or
categorizes
9
Example of ordinal level of measurement:
Pain scale assessment of the patients:
”Please rate your pain over the last week”
After 1 week of therapy
0
=no pain 1
=mild pain
2
=moder ate pain
3
= severe pain
4
= very severe pain
5
= worst possible pain
After 2 weeks After 3 weeks After 4 weeks
All sections maybe not equal as different for one person to another
10
Example of Ordinal Level of Measurements
Number of cases treated
Osteo- arthritis
Rheumatoid arthritis
Traumatic arthritis
In outpatient dept. 2 10 1
In inpatient hospital care
4 6 4
In ambulatory care (home care)
1 3 1
Total number of cases
7 19 6
•Ordinal measurement level is not appropriate for arithmetical computation.
•Simply ordinal level of measurement can be extension to a, b, c...,n, in which it indicates that a > b > c> ... n, in
some property.
11
3) Interval level measurement (scales):
This measurements include all the qualities of the ordinal level measurements and also include units that are equal in size.
Also the distances between levels are equal. This permit the use of arithmetic operations and the zero point is
arbitrary. (average, mean)
(e.g. centigrade temperature measurement, where zero does not indicate the absence of heat but rather is an arbitrary point).
12
Examples of interval measurement scale
Temperature: 0°,1°,2°,3
Childrens age: 0-1, 1-2,2- 3,3-4,…
All cat. are equal and can be added.
Pain scale with regular intervals ( each number is une cm distant)
No pain moderate pain worst
possible pain 0 1 2 3 4 5 6 7 8 9 10
13
4) Ratio level of measurements:
Ratio level of measurements include all the qualities of the interval level of measurement.
This level has the highest level of validity and also includes a zero point that is absolute (e.g.: Kelvin scale of temperature, where zero-degree Kelvin is absolute zero, indicating the absence of heat).
In the ratio level of measurements, arithmetic operations are possible ( average, means, standard deviations).
Numbers on the scale indicate the actual quantitative data of measured property.
14
Examples of ratio levels of measurements
Degrees of exam:
0/20
0,1,2,3,4 are ratios on 20
ROM: of the shoulder on 45°/90°
0° = no range or absence of movement.
1° ROM
2° ROM
Weight and height
measurements are ratio scales
15
Conclusion
Nominal
Ordinal
Interval
Ratio levels of measurements
Some data collection have to be more precise than others to be giving relevant information( i.g.
areas of pain compared to degree of pain sensation).
The therapist will always try to be as precise as possible to draw conclusions and summaries as clear as possible.
are types of ways to evaluate and gather information
16
Examples of measuring spasticity
Nominal level: measure areas, segments or muscles
affected by spasticity: Right lower limb more distally in the quadriceps, sartorius, gastrocnemius.
Ordinal level : classify the spasticity from:
no spasticity- slight sp.- moderate sp.- severe sp.- very severe.
Interval level :the spasticity measure is graded from 1 to 5 with all intervals are the same on the scale.
Ratio type of measurement level = the most sensitive as it measures the degrees of AROM in the lower limb or PROM.
Some levels are not always possible to be applied.
17
THANK YOU
18
Reliability, Objectivity and Validity
All measurements should have some
“qualities” otherwise they might not mean or measure “well enough”.
Measurement must be reliable and objective and the result must be valid.
19
Objectives of the lecture
Clarify the concepts of reliability, objectivity and validity.
Explain the types of validity:
Face validity,
Construct validity,
Content validity
and criterion-related validity.
20
Reliability
If a muscle test is repeated by one or more therapists who obtain the same score every time; then the test is reliable.
The key to reliability for manual muscle testing is to follow the standard procedures, performing the test in the same way each time and in the same way that
other therapists perform it. standardized
Reliability is also increased if the therapist gives clear instructions to the patient.
Definition :Reliability is the repeatability and the extent to which comparable results are achieved every time a test is repeated.
A reliable measure is one that is consistent.
21
Inter-rater and intra-rater reliability
Evaluation procedures should exhibit
inter-rater and intra-rater reliability:
* Inter-rater reliability means that another person who performs the test should arrive at the same results, to an acceptably extent.
* Intra-rater reliability means that one same person should come out with the same results on every repetition of the test, within acceptable level.
22
Estimation of Reliability
There are 3 methods that estimate reliability of certain measurement tool;
test-retest, (several times the same test)
parallel-forms ( the test is applied to
same situations but different examiners)
and split-half methods ( the test is given to two different groups placebo and
positive).
Example:Inter-rater reliability test was done to examine the effects of goniometer size on the reliability of passive shoulder joint
measurements.
It is concluded that goniometric passive measurement of the range of the shoulder
joint motion can be highly reliable when taken by a single therapist (intra-rater reliability), regardless of the size of the goniometer.
23
b) Objectivity
Objectivity means that the findings are reported without distortion by personal opinion or feelings.
Therapists should not let concern for the patient to influence the results of an evaluation procedure.
Objectivity (Cont.)
In manual muscle testing, the most
difficult area, in which to be objective, is deciding whether the resistance the
patient can tolerate is minimal, moderate or maximal.
If the patient's weakness is unilateral, test the opposite side and use the result as the baseline for normal.
If the patient has bilateral involvement, the therapist must relay on experience in testing other patients and normal
subjects to know what is normal for a particular muscle in a person of a given age, sex, size and occupation.
24
25
Validity
In muscle testing, therapists are testing the strength of a specific muscle.
i.g. For a muscle test to be valid, the therapist must know the location and function of the muscle being tested and the location and function of surrounding muscles.
Validity of assessment means that the therapists
evaluate exactly what they are going to do and that the results are correct or true.
Validity means that a test actually measures what it is supposed to measure.
26
Types of Validity:
1. Face validity:
Many of the measurements used in PH.TH appear to be based
on the assumption of face validity i.e. they are assumed valid as a result of inference.
Face validity for a measurement is a lot-like the shine on a new car.
It is a nice thing to have but you can not get very far more than nice → what you see (appearance).
E.g; the meter as measuring tape appears well designed and suited for measuring the length of a limb.
E.g. the scale appears an object of measuring the weight of someone.
Face validity is the appearance of a justifiable use for a measurement but does not mean there have any data or theory to support the use.
27
2. Construct validity:
Construct validity of a measurement is made through the logic; using existing knowledge.
It is a theoretical form of validity which supports the use of a measurement for a specific inference.
There is no absolute way of knowing when measurement has construct validity.
28
Construct Validity (examples )
E.g the manual muscle test was developed with a clear construct in mind. (When poliomyelitis was widespread, manual muscle test was developed to characterize the weakness and the construct was simple:
fully innervated muscles can generate more tension than partially
innervated muscles; while totally denervated muscles can generate no tension)
E.g;The weighing scale was designed to precisely measure the weight by the construct that the persons body weight will move the component weights of the scale and the heavier the person the more the weight lifted.
Pain scale is based on the knowledge that pain is perceived in different gradients by the transmission of nerve impulses.
29
3. Content validity
Content validity deals with how measurement schemes relate to their constructs,
i.e. relating a measuring tool to a general theoretical framework in order to determine whether this tool is linked to the theoretical assumption.
The classic test of content validity is to ask whether we have chosen an adequate group of items to measure from the larger group of possible items, defined by our construct.
Example:To evaluate effect of contrast bath on oedema of the hand:
- compare test before and after
by measuring wrist, fingers circumference with tape measurer
or by measuring the volume of the hand
30
Content validity (cont.)
I.e. the type of scale to measure the weight for adult or infant as per the size of the scale.
Gait is measured in steps or in meters of ambulated steps, or number of stairs climbed.
Strength is measured by lifting an amount of weight for large muscles , or by squeezing resistive objects for small muscles.
31
4. Criterion-related validity:
Construct validity deals with the theoretical basis for a
measurement. (Strength is measured in kg.lifted as it is known as scale for measuring something heavy.)
Content validity deals with implementation of theory.
Both construct and content validity are based on theory and can never be directly tested. This is in contrast to
criterion-related validity.
Criterion-related validity represents the ultimate test of validity.
32
4. Criterion-related validity:
To demonstrate this validity, a measurement is compared to a criterion to determine whether or not the
inference was appropriate.
I. E.g. criterion is the weight:Test if strength is
improving → pt. lifts more weights. If you test less strength, the results should vary and show decrease
→ lifts less weight.
II. E.g. The goniometer will measure the large or small ROM.
33
Summary
Types of validity:
Face Validity (from the appearance)
Construct Validity (from the theory)
Content Validity ( from theory applied to practice of measurement)
Criterion -related validity ( compared to a criterion, to what we want to measure)
34
