This study is a quasi-experiment as there are pre-existing groups, younger and older adults. Instead of an independent variable, this study has a subject variable - age. The dependent variable is life satisfaction (operationalized the score on the life satisfaction questionnaire). The researchers draw an invalid conclusion. As this study is quasi-experimental, only descriptive results can be reported and not causal results. The researchers should not have stated that old age causes increased life satisfaction, but rather, that older adults could be described as having higher life satisfaction than younger adults. It may be that the older adults have always had high life satisfaction. While only descriptive results can be given, that does not mean that inferences about this result could not be applied to the larger population. I can say that older adults (similar to my initial sample) are likely to have high life satisfaction. I just can not say what causes this high score.
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