Page 107 - DMGT209_QUANTITATIVE_TECHNIQUES_II

Quantitative Techniques-II

Notes 15. Maturation is similar to …………….
16. ………..in selection occurs because two groups selected for experiment may not be identical.

6.7 Experimental Designs

The various experimental designs are as follows:
 Purely post-design
 Before-after design
 Factorial design
 Latin square design
 Ex-post facto design

6.7.1 Purely Post-design

In this design, the dependent variable is measured after exposing the test units to the experimental
variable. This can be understood with the help of following example:

Example: Assume M/s Hindustan Lever Ltd wants to conduct an experiment on the
“Impact of free sample on the sale of toilet soaps”. Small samples of toilet soaps are mailed to
selected customers in a locality. After one month, a coupon of 25 paise off on one cake of soap is
mailed to each customer to whom free samples were sent earlier. An equal number of these
coupons are also mailed to people in another locality in the neighborhood. The coupons are
coded to keep an account of the number of coupons redeemed from each locality. Suppose, 400
coupons were redeemed from the experimental group and 250 coupons were redeemed from
the control group. The difference of 150 is supposed to be the effect of free samples. In this
method, the conclusion can be drawn only after conducting the experiment.

6.7.2 Before-After Design

In this method, measurements are made before as well as after the design.

Example: Let us say that, an experiment is conducted to test an advertisement which is
aimed at reducing alcoholism.

Attitudes and perceptions towards consuming liquor are measured before exposure to the
advertisement. The group is exposed to an advertisement, which tells them the consequences,
and their attitudes are again measured after several days. The difference, if any, shows the
effectiveness of that advertisement.
The above example of “Before-after” suffers from validity threat due to the following.

Before Measure Effect

It alerts the respondents to the fact that they are being studied. The respondents may discuss the
topics with friends and relatives and modify their behaviour accordingly.

Instrumentation Effect

This can be due to two different instruments being used – one before and one after. A change in
the interviewers before and after, results in the instrumentation effect.

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