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DISC profiling since 1994
22
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(214) 613-3983
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Features
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Pricing
Training
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Individual Reports
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DISC: A Layman's Guide
What is DISC?
Video: Introduction to DISC
DISC Profile Interpretations
DISC Factors
Team Building with DISC
History and Development of DISC
Personality Types
Applications: Putting DISC to Work
Validity and Reliability of DISC
Knowledge Base
(214) 613-3983
E-mail us
Skype us
Contact Details

3.1 Reliability

In the reliability exercise, the test-retest reliability technique was used. According to this method the same instrument is applied to the same respondents at a later stage and the correlation between the two scores is then calculated (Huysamen 1980:54; Mulder 1981:211).

The questionnaire was administered by the respective people participating in the exercise. All of these participants are trained in Discus and how to administer the instrument. The instrument was administered for the first exercise to obtain a pretest score. The exercise was then repeated with the same respondents after a period of three months in order to obtain a post-test score.

A statistical evaluation of the raw data, resulting from the exercise, was then obtained by using the SAS system, reflecting Pearson's Product-moment correlation coefficient (coefficiency of stability).

3.1.1 The Questionnaire

The questionnaire consists of 24 questions each of which presents the respondents with four options. The respondents' task is to select one of the options that most closely resembles themselves, and one that least closely describes them. The respondents are required to focus on the role they fulfil in their work environment and answer all the questions in relation to that role.

  • Phrase-based
    The phrase-based question set contains questions of the form 'Behaving compassionately towards others' or 'Persuading others to your point of view'.
  • Adjective-based
    The adjective-based question set contains words such as 'kind-hearted', 'persuasive' and 'modest'.

For the purpose of this exercise the phrase-based questionnaire was used because it is easier to understand.

3.1.2 Sampling Technique and Size

Various companies were approached to assist with the exercise as reflected in table 1.

TABLE 1: COMPANIES USED
Technikon Natal
Edgars Group (Gauteng)
Toyota South Africa (KZN)
NBS
BB Cereal

The questionnaire was administered to 90 respondents. These respondents were randomly selected from the respective companies reflected in table 1. A statistical evaluation of the raw data resulting from the testing was then obtained by using the SAS system reflecting Pearson's product-moment correlation coefficient.

3.1.3 Results

The correlation analyses are reflected in table 2.

TABLE 2: CORRELATION MATRIX:
BEFORE AND AFTER SCORES
Pearson's Product-Moment Correlation Coefficient
r = values
p = values
D
BEFORE
I
BEFORE
S
BEFORE
C
BEFORE
DOMINANCE
AFTER
r=0.72831
p=0.0001
r=0.11048
p=0.2972
r=0.61917
p=0.0001
r=0.16192
p=0.1252
INFLUENCE
AFTER
r=0.22558
p=0.0325
r=0.64578
p=0.0001
r=0.5282
p=0.6210
r=0.33619
p=0.0012
STEADINESS
AFTER
r=0.58452
p=0.0001
r=0.14199
p=0.1819
r=0.73004
p=0.0001
r=0.22517
p=0.0329
COMPLIANCE
AFTER
r=0.17989
p=0.0898
r=0.36256
p=0.0004
r=0.17270
p=0.1036
r=0.55000
p=0.0001

The significance level chosen for this instrument is alpha = 5%. Where the p-value is less than 0.05, the scores show a significant correlation. In the reliability analysis the p-value in all the cases is as low as 0.0001. This indicates significance at alpha = 0.001. It can therefore be said the correlation is significant at 1% level.

The reliability coefficient of the measuring instrument is close to 1 and can therefore be seen as reliable.

3.2 Validity

3.2.1 Content Validity

Content validity of the instrument is determined when the instrument is designed. Content validity refers to the extent in which the instrument measures what it is supposed to measure (De Wet, De K Monteith, Steyn & Venter 1981:146; Huysamen 1980:95; Mulder 1989:219).

Each question in the Discus instrument was evaluated by the designers of the instrument, namely Axiom. Although content validity was done by Axiom, the researcher also decided to measure validity in terms of criterion-related validity.

3.2.2 Criterion-related Validity

By applying the method of criterion-related validity, an exploratory study was done by correlating all 15 Factors in Cattell's 16-PF with the four dimensions in the Discus. Factor B was not considered as doubts exist in the literature as to the validity of Factor B (intelligence) within a personality test.

Criterion-related validity was restricted to validation procedures in which the test scores of a group of respondents are compared with ratings of other measurements (Aiken 1994:96).

Nunally (1978) claims that it is unrealistic to expect exceptionally high correlation coefficients and Anastasi (1976) says that coefficients of 0.20 and higher can be significant.

3.2.3 Sampling Size and Technique

In this exercise employees of the Edgars group, Toyota South Africa and Technikon Natal were used. It was therefore decided to use the Discus and Cattell's 16-PF (Form A) for this exercise.

In an attempt to determine a correlation between the Discus dimensions and Cattell's 16-PF, scores on the 16-PF were obtained from 120 employees employed by the abovementioned companies. These respondents were randomly selected from line managers, middle managers, professionals and junior officials. The sample was drawn from all organisational functions and cultural groups within the organisations.

3.2.4 Measuring Instruments

3.2.4.1 The Discus Questionnaire
This questionnaire has already been discussed in paragraph 3.1.1.

3.2.4.2 Cattell's 16-PF
The 16-PF is specifically constructed for the purpose of determining individual attitudes, perceptions and personality characteristics. It was developed by R.B. Cattell and published in 1949. The A and B Forms of the test consist of 187 items each and are suitable for adults with at least standard 10 or equivalent education. The 16-PF can be used for the evaluation of personality in people of different population groups because it is culture friendly (Prinsloo 1992:21-22).

Cattell applied the technique of factor analysis and obtained a set of 16 primary factors. The rationale behind the 16-PF is that a questionnaire which is based on revealed traits, obtained through mathematical techniques from a large pool of possible personality descriptions, is capable of measuring reliably and validly the true constructs present in humans.

The general purpose of the 16-PF is to describe testees' personality and predict behaviour using a set of selected, structured items. The test has many practical applications, some of which are mentioned below:

  • Career counselling
  • Fruitful employment in industrial and career settings
  • Counselling
  • Clinical settings
  • Extremely useful research


The results of a factor analysis completed by Cattell identified the following 16 factors (table 3).

TABLE 3: THE HIGH AND LOW FACTORS OF THE 16-PF
LOW SCORES
FACTOR
1 2 3 4 5 6 7 8 9 10
HIGH SCORES
Reserved
A
Outgoing
Dull
B
Bright
Easily Upset
C
Calm
Submissive
E
Dominant
Serious
F
Impulsive
Frivolous
G
Responsible
Shy
H
Bold
Tough-minded
I
Tender-minded
Trusting
L
Suspecting
Practical
M
Fanciful
Forthright
N
Calculating
Secure
O
Apprehensive
Conservative
Q1
Liberal
Group-dependent
Q2
Self-sufficient
Uncontrolled
Q3
Controlled
Relaxed
Q4
Tense

For interpretation purposes, factor scores of 1 to 3 and 8 to 10 are considered. The low numbers of each factor are pictured as portraying one extreme of the profile and the high numbers as portraying the other. It should be pointed out that Cattell, in analysing all 16 factors, came up with clusters of several adjectival descriptors for each factor. Table 3 depicts words representative of factor clusters. The Kuder-Richardson 8-method was used to determine the reliability of the 16-PF. Table 4 reflects the reliability figure for each factor.

TABLE 4: RELIABILITY SCORES FOR 15 FACTORS OF 16-PF REFLECTING THE KR-8 SCORE
16-PF FACTORS
KR-8
A
0.647
C
0.561
E
0.563
F
0.662
G
0.661
H
0.741
I
0.585
L
0.487
M
0.353
N
0.352
O
0.549
Q1
0.370
Q2
0.631
Q3
0.476
Q4
0.720
SOURCE: Prinsloo 1991:23

3.2.5 Procedure

The Discus and the 16-PF were administered by trained and registered psychologists. The marking and interpretation of the 16-PF questionnaires were done manually by the researcher, a registered psychologist, and by psychologists from the HSRC.

3.2.6 Statistical Analysis

Pearson's product-moment correlation coefficient was computed, using the SAS-system to determine a correlation between the identified fifteen 16-PF factors and the Discus dimensions.

3.2.7 Results

The 120 questionnaires that were returned were statistically analysed. Scores for each of the fifteen 16-PF factors as well as the Discus dimensions were correlated. The individual Discus variable scores were then correlated with all the fifteen factors of the 16-PF, resulting in significant correlations at 1% level of significance and at 5% level of significance. The results of these findings are reflected in tables 5A (p-values) and 5B (r-values).

TABLE 5A: COMPARISON BETWEEN THE DISCUS DIMENSIONS AND THE FIFTEEN FACTORS OF THE 16-PF. PEARSON'S PRODUCT-MOMENT CORRELATION COEFFICIENT
(5% LEVEL OF SIGNIFICANCE)
(1% LEVEL OF SIGNIFICANCE)

p-values

Discus Dimension
16-PF Factor
1% Level of Significance
(99%)
16-PF Factor
5% Level of Significance
(95%)
Dominance
Q1
X (Q2, E)
X (G, L, Q1)
0.0004
0.0003
0.0083
E
Q2
-I
0.0141
0.0331
0.0110
Influence
A
-Q2
H
0.0011
0.0011
0.0070
F
-Q3
0.0146
0.0426
Steadiness
None
None
-E
-Q1
0.0363
0.0231
Compliance
-E
Q2
-F
-H
0.0095
0.0092
0.0045
0.0025
-G
O
0.0244
0.0446

TABLE 5B: COMPARISON BETWEEN THE DISCUS DIMENSIONS AND THE 16-PF FACTORS

r-values
Discus Dimension
16-PF Factor
1% Level of Significance

r-values
16-PF Factor
5% Level of Significance

r-values
Dominance
Q1
X (Q2, E)
X (G, L, Q1)
0.32128
0.32846
0.24180
E
Q2
-I
0.22442
0.19551
0.23320
Influence
A
-Q2
H
0.29825
0.29593
0.24791
F
-Q3
0.22519
0.18776
Steadiness
None
None
-E
-Q1
0.19215
0.20907
Compliance
-E
Q2
-F
-H
0.23678
0.23768
0.26000
0.27583
-G
O
0.20715
0.18529

Problem Statement Discussion and Conclusion

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