After only

This is used by researchers who are not overly concerned about the strength of their findings or internal/external validity. Symbolically the design appears as:

A single group of subjects is exposed to a treatment, and the subjects' responses are recorded once. The subjects are usually selected in a subjective (non-random) manner.


Special pence-off coupons for a shampoo are hand-distributed to women in a shopping mall. The number of these coupons turned in is recorded and a judgement is made of the success of the coupon promotion.

With this form of design, no data exist that can be used to assess the influence of extraneous factors during the period. There is also no evidence about the subject's behaviour before the treatment. The design is simple to use, but its results are not very enlightening. There is no indication, for example, of how the treatment may have changed customer behaviour.

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