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Understanding Correlations
This is a practice exercise. To see example answers, click on the question (clicking on the answer goes back to the questions.)
Correlational studies show relationships between variables. If high scores on one variable predict high scores on the other, the correlation is positive. Likewise, low scores on one predicting low scores on the other would still reflect a positive correlation because the change in one is in the same direction as the other.
A negative corelation is found when change in one
variable is accompanied by change in the opposite direction in the other variable.
Showing that two variables are related does not
justify claiming that a causal relationship exists. There may be a causal
relationship, but other explanations usually exist. For example, the variables may
be related because both have a causal relationship with a third variable. So, if you
find that A is correlated with B, any of the following
may explain the cause underlying that relationship:
For each of the correlational studies described below, decide whether the correlation is positive or negative and give two alternative explanations for each finding.
1. A study of married couples showed that the longer they had been married, the more similar their opinions on social and political issues were.
2. An intelligence test was given to all the children in an orphanage. The results showed that the longer children had lived in the orphanage, the lower their IQ scores.
3. In a study of American cities, a relationship was found between the number of violent crimes and the number of stores selling violence-depicting pornography.
4. A college professor found that the more class absences students have, the lower their grade in the course tends to be.
5. A politician running against a candidate who had been in office for eight years pointed out that violent crime had increased during those eight years even though the administration appropriated more and more money to fight crime.
(Adapted from V. Diehl (1999). New York: Longman.)
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