Page 55 - DMGT404 RESEARCH_METHODOLOGY

Unit 3: Research Design

5. Selection bias Notes
6. Experimental mortality
1. History: History refers to those events, external to the experiment, but occurs at the same
time, as the experiment is being conducted. This may affect the result. Example: Let us say
that, a manufacture makes a 20% cut in the price of a product and monitors sales in the
coming weeks. The purpose of the research, is to find the impact of price on sales. Mean
while if the production of the product declines due to shortage of raw materials, then the
sales will not increase. Therefore, we cannot conclude that the price cut, did not have any
influence on sales because the history of external events have occurred during the period
and we cannot control the event. The event can only be identified.
2. Maturation: Maturation is similar to history. Maturation specifically refers to changes
occurring within the test units and not due to the effect of experiment. Maturation takes
place due to passage of time. Maturation refers to the effect of people growing older.
People may be using a product. They may discontinue the product usage or switch over to
alternate product.

Example:
(a) Pepsi is consumed when young. Due to passage of time the consumer becoming older,
might prefer to consume Diet pepsi or even avoid it.

(b) Assume that training programme is conducted for sales man, the company wants to measure
the impact of sales programme. If the company finds that, the sales have improved, it may
not be due to training programme. It may be because, sales man have more experience
now and know the customer better. Better understanding between sales man and customer
may be the cause for increased sales.
Maturation effect is not just limited to test unit, composed of people alone. Organizations also
changes, dealers grow, become more successful, diversify, etc.

3. Testing: Pre-testing effect occurs, when the same respondents are measured more than
once. Responses given at a later part will have a direct bearing on the responses given
during earlier measurement.

Example: Consider a respondent, who is given an initial questionnaire, intended to measure
brand awareness. After exposing him, if a second questionnaire similar to the initial questionnaire
is given to the respondent, he will respond quiet differently, because of respondent's familiarity
with the earlier questionnaire.
Pretest suffers from internal validity. This can be understood through an example. Assume
that a respondent's opinion is measured before and after the exposure to a TV commercial
of Hyundai car with Shahrukh Khan as brand ambassador. When the respondent is replying
the second time, He may remember, how he rated Hyundai during the first measurement.
He may give the same rating to prove that, he is consistent. In that case, the difference
between the two measurements will reveal nothing about the real impact.
Alternately some of respondents might give a different rating during second measurement.
This may not be due to the fact that the respondent has changed his opinion about Hyundai
and the brand ambassador. He has given different rating because, he does not want to be
identified as a person with no change of opinion to the said commercial.

In both the cases of above, internal validity suffers.

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