KNOWLEDGE FOR THE BENEFIT OF HUMANITYKNOWLEDGE FOR THE BENEFIT OF HUMANITY

RESEARCH METHODOLOGY (HFS4343)

VALIDITY AND RELIABILITY OF A RESEARCH INSTRUMENT

Dr. Dr. MohdMohd RazifRazif ShahrilShahril

School of Nutrition & Dietetics School of Nutrition & Dietetics

Faculty of Health SciencesFaculty of Health Sciences

UniversitiUniversiti Sultan Sultan ZainalZainal AbidinAbidin

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Topic Learning Outcomes At the end of this lecture, students should be able to;

• describe the concept of validity

• explain different types of validity

• describe the concept of reliability

• explain factors affecting the reliability of a research

instrument

• illustrate methods of determining the reliability of an

instrument

• differentiate validity and reliability in qualitative research

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

The concept of validity

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Is the research Is the research investigation investigation

providing answers providing answers to the research to the research questions for questions for which it was which it was undertaken?undertaken?

If so, is it providing If so, is it providing these answers using these answers using

appropriate methods appropriate methods and procedures?and procedures?

S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

The concept of validity

• Are we measuring what we think we are measuring?

• Validity is the ability of an instrument to measure

what it is designed to measure.

• Key questions;

– Who decides whether an instrument is measuring what it is

supposed to measure?

– How can it be established that an instrument is measuring what

it supposed to measure?

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Types of validity in quantitative research

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Face and Face and content content validityvalidity Concurrent Concurrent

and and predictive predictive

validityvalidity

Construct Construct validityvalidity

S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Face and content validity

• The judgement that an instrument is measuring what it is

supposed to.

– primarily based upon the logical link between questions and

objectives of the study.

• Advantage: easy to apply

• Face validity – establishment of logical link between

questions and objectives of study

• Content validity – assessment if items and questions

covers the full range of the issue being measured.

– Judge which statements or questions represent the issue they

are supposed to measure

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Face and content validity (cont.)

• Problems;

– Judgement is based upon subjective logic

– The extent to which question reflect the objectives of a study

may differ.

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Concurrent and predictive validity

• Predictive validity – judged by how well an instrument

can forecast an outcome.

• Concurrent validity – judged by how well an instrument

compares with a second assessment concurrently done.

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Construct validity

• Construct validity – determined by ascertaining the

contribution of each construct to the total variance

observed in a phenomenon.

• Based upon statistical procedure.

• The greater the variance attributable to the construct, the

higher the validity of the instrument.

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

The concept of reliability

• Reliability is if a research tool is consistent and

stable hence predictable and accurate.

• The greater the degree of consistency and stability in a

research instrument, the greater the reliability.

• A scale or test is reliable to the extent that repeat

measurements made by it under constant conditions will

give the same result.

• Reliability is the degree of accuracy or precision in the

measurements made by a research instrument.

– The lower the degree of ‘error’ in an instrument, the higher the

reliability.

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Reliability vs. Validity

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Factors affecting reliability

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The wording of questions

The physical setting

The respondent’s or interviewer mode

The regression effect

The nature of interaction

S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Methods of determining the reliability

• Internal consistency procedures – items or questions

measuring the same phenomenon, should produce

similar results irrespective of their number in an

instrument

– The split-half technique

• External consistency procedures – compare findings

from two independent process of data collection with

each other as a means of verifying the reliability of the

measure

– Test/retest

– Parallel form of the same test

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Split-half technique

• To correlate half of the items with the other half in a

research instruments

• Questions are divided in half in such way that any two

questions intended to measure the same aspect fall into

different halves.

• The scores obtained by administering the two halves are

correlated.

• Reliability is calculated using product moment correlation

between scores

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Test/ retest (repeatability test)

• An instrument is administered once, and then again,

under the same or similar conditions.

• The ratio between test and retest score is an indication

of the reliability of the instrument

– The greater the value of the ratio, the higher the reliability of the

instrument

• Advantage - it permits the instrument to be compared

with itself.

• Disadvantage – a respondent may recall the responses

that they gave in the first round

– Overcome by increasing the time span between two tests

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Parallel forms of the same test

• Two instrument intended to measure the same

population is constructed and administered to two similar

population.

• The results obtained from one test is compared with

another

– If similar, the instrument is reliable.

• Advantage – does not suffer from the problem of recall

and time lapse between two test is not required.

• Disadvantage – need to construct two instrument instead

of one.

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S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Validity & reliability in qualitative

research

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Traditional criteria for judging quantitative research

Alternative criteria for judging qualitative research

Internal validity Credibility

External validity Transferability

Reliability Dependability

Objectivity Confirmability

S C H O O L O F N U T R I T I O N A N D D I E T E T I C S • U N I V E R S I T I S U L T A N Z A I N A L A B I D I N

Validity & reliability in qualitative

research

• Credibility

• Transferability

• Dependability

• Confirmability

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Thank YouThank You

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