No Manipulation Check

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For example, researchers are interested in how mood affects memory. There are a number of effective strategies for producing a particular mood including exposure to music and autobiographical writing. As part of the study, they ask one group of participants to write about the happiest, most joyful event they experienced in the past 6 months. A second group was asked to write about the saddest event that they have experienced. A final group was asked to describe in as much detail as possible the route they traveled to arrive at the laboratory. They are then asked to read and study a lengthy passage that included descriptions of both sad and happy events.

After a distracter task, they are given a series of words and asked to identify which ones appeared in the passage.

You hypothesize that those asked to write about a happy event will recall more positive words and those asked to write about a sad event will recall more negative words. A manipulation check is something included in the study that will tell us whether the experimental manipulation successfully produced different mood states. As part of the distracter task, participants are asked to complete some questionnaires that ask about personality and background characteristics. Included in this packet of questionnaires is a brief mood inventory.

Later analysis of the mood survey tells us that those in the happy mood condition reported a better mood and those in the sad condition reported more negative moods. When the researchers interpret the results of the hypothesis tests, they will do so knowing that the experimental manipulation successfully induced the desired mood states.