This recent feature in the Wall Street Journal reviews several studies on how IQ changes over time.

The studies were conducted by a variety of researchers using a variety of methods.  Here is one example:

A 30-year study at the National Institute of Mental Health found that people whose work involves complex relationships, setting up elaborate systems or dealing with people or difficult problems, tend to perform better over time on cognitive tests. Test scores of people whose jobs are simple and require little thought actually tend to decline, according to the research, published in 1999 in Psychology and Aging.

a) This seems to be a quasi-experiment.  What type is it?  What are the main variables?  Can you sketch the results described above?

Here is another study explained in the article: 

New tasks stimulate the brain most. When researchers at the University of Hamburg subjected 20 young adults to one month of intense training in juggling, they found an increase in the corresponding gray matter in the brain as early as seven days after the training began. The added gray matter receded when the training was stopped, although the participants were still able to juggle, says the study….

b) What kind of dependent measures were used in this study–self-report, behavioral, or observational?

c) The design of the study is difficult to discern from this description alone.  The journalist does not mention a comparison group, so we might wonder if there is only be one group in the study–the group that learned to juggle.  What are the problems with using only one group in a study like this?  How might the researchers control for these internal validity threats? (You can look up the original study to find out what the real design was!)

d) Assume that the study above is an example of an interrupted time series design.  Sketch a graph of the results, based on the description given by the journalist.