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Confounding Variables

Confounding Variables . Definition. Confounding variables are two variables (explanatory or lurking variables) that are confounded when their effects on a response variable cannot be distinguished from each other. Example.

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Confounding Variables

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  1. Confounding Variables

  2. Definition • Confounding variables are two variables (explanatory or lurking variables) that are confounded when their effects on a response variable cannot be distinguished from each other.

  3. Example • A soccer coach wanted to improve the team's playing ability, so he had them run two miles a day. At the same time the players decided to take vitamins. In two weeks the team was playing noticeably better, but the coach and players did not know whether it was from the running or the vitamins.

  4. Case Study • If, for example, subjects in one group are simultaneously tested in a room with the heat set at 70 degrees whereas subjects in another group are simultaneously tested in a nearby identically appointed room with the heat set at 60 degrees, the obtained differences in performance could be attributed to any of three factors.

  5. It could be due to the random assignment of subjects (i.e. to chance). It could be due to the different temperatures in the two rooms. It could, however, be due to some confounding factor such as differences in ambient illumination that result from unnoticed differences in the orientation of each room with respect to the sun.

  6. In any experiment an appropriate statistical test can help in the decision as to whether or not to attribute the results to chance, but only the most careful analysis of the actual conditions of the experiment can suggest whether or not the result might be due to a confounding factor.

  7. Lurking Variables

  8. Definition • A lurking variable is a variable that has an important effect on the relationship among the variables in a study but is not included among the variables studied.

  9. Example • There's this guy who's going to clean the windows of a mental asylum. A patient follows him shouts to him "I gotta secret, I gotta secret...", he ignores the patient. Again the patient follows him, but he ignores his cries. By the time he's nearly finished the building, he's really curious about what the patients secret is, so he decides to ask the patient.

  10. The patient pulls a matchbox out of his pocket, opens it and puts it on a table. Out crawls this little spider. The patient says "spider go left", and the spider walks to it's left a bit. Then he says "spider go right", the spider walks to its right a little bit. He says "spider turn around, walk forward then go right", and sure enough the spider turns around, walks forward, and then goes right a bit. The window cleaner is amazed "Wow! He says, that's amazing!", "No, that's not my secret says the patient, watch".

  11. He picks up the spider in his hand and pulls all its legs off then puts it back on the table. "Spider go right", the spider doesn't move, "spider go Left", the spider doesn't move, "Spider turn around" again the spider doesn't move. "There!" he says, "that's my secret, if you pull all a spiders legs off they go deaf....................

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