Everyday Research Methods

Musical skill: Why does an early start seem to help?

People might start musical training early because they are living in musical families or show early evidence of musical talent. 
Photo credit: Artem Furman, Alamy stock photo

What accounts for musicality? Some people are highly skilled and accomplished musicians, while others express no aptitude. A recent correlational study tried to understand why some people are more musically accomplished. A summary of this research appears on the APS website, and the original empirical article appears in the journal Psychological Science. 

The researchers used a sample of 310 professional musicians as well as a large sample of twins (which they called "amateur musicians"). The twin sample came "from an existing research project, the Study of Twin Adults: Genes and Environment (STAGE)." The twin sample enabled the researchers to estimate genetic and environmental similarities on musicality.

The participants completed measures of musical aptitude (e.g., tests of their accuracy at pitch and rhythm) and musical achievement (e.g., having performed publicly or won prizes). Researchers also asked each person what age they had started learning music. They asked how many hours per week they'd practiced at different points in their lives. The journalist summarized one of the core results:

By comparing the results from these two independent studies, the researchers were able to show that an earlier start age is associated with musical aptitude, both in amateurs and professional musicians...

Questions for students appear in gray throughout this post:
a) Sketch two scatterplots of this result described in the green quoted text above--one scatterplot for professional musicians and one for amateurs. The x and y axes will be the same on the two scatterplots--be sure to label these carefully. Will your scatterplots show positive or negative relationships? 

 

Now, it might make sense that starting musical training at an earlier age is associated with better musical aptitude simply because of total practice time. That is, people who start training earlier have practiced more hours, and practicing more hours is usually associated with more musical skill. In other words, we might sketch this, third-variable proposal:

According to the study, was total practice time a third variable, explaining why starting age was associated with greater aptitude? Consider this full quote from the journalist's summary: 

By comparing the results from these two independent studies, the researchers were able to show that an earlier start age is associated with musical aptitude, both in amateurs and professional musicians, even after controlling for accumulated practice time.

This quote means that even though practice time is usually associated with greater aptitude, this was not the reason why starting earlier was associated with greater aptitude. The results from a regression table might have looked like this:

DV/criterion variable: Musical aptitude
IV/predictor variable:                 Beta
Age starting musical training          -.21**
Total practice time                               .03           
(The betas above are simplified versions of those reported in the original journal article, Table 3, for the musician sample)

Question
b) Write a sentence describing what the beta of -.21** means. 

Therefore, it wasn't total practice time that accounted for the benefit of starting musical training early. On to the next explanation:

[The researchers] then evaluated starting age in a manner that accounted for the genetic data from the STAGE study.  

The results indicate that genetic factors—possibly related to musical interest and talent—have a substantial influence on the age individuals start music practice and their future musical aptitude. When controlling for familial factors, namely shared genetic and environmental influences, such as a home environment that is steeped in music, there was no additional association between an earlier start age and musicality. 

So, in other words, the researchers were proposing this explanation:

And they found results that supported this explanation. The statistical calculations that are used in twin studies are actually beyond the scope of this course and book--so you'll have to trust the researchers here. Suffice it to say that when they controlled for genetic interest or talent, there was no longer an association between age at starting training and musical aptitude.

c) Consider the construct validity of two of this study's variables: Musical aptitude and age at starting training. What questions could you ask to evaluate the construct validity of these measures? 

d) Here is a challenge question: In the empirical journal article (Table 2) the researchers reported that the correlation between between total practice hours and musical aptitude in the professional sample was r = .05, while the same association in the amateurs (i.e., the twins) was r = .30. One reason the correlation was weaker in the professional musician sample might have been restriction of range. Sketch two scatterplots--one for each sample but with the same x and y axes--that illustrates how restriction of range might have limited the correlation in the professional musician sample. 

Meta-analyses: Strength training treats depression and anxiety

Strength training seems to improve both depression and anxiety, according to two meta-analyses. Photo credit: romanchazov27/Deposit Photos

Many of us start the new year resolved to improve our exercise habits. Exercise, of course, is great for our physical health, and we also know that aerobic exercise (i.e., "cardio") can improve mood. The benefits of aerobic exercise on depression and mood have been well-documented by several studies (here's an example of one meta-analysis). 

A recent article in the Washington Post describes the benefits of strength, or resistance, training for depression. The piece provides a good example of how a journalist covers meta-analysis for a popular audience.

The author himself suffers from depression, and starts his article by explaining his own workout strategy:

It’s strength training — the muscle-building, body-toning and sometimes grunt-inducing workout — that has helped transform my chronic mental illness into better mental health. In fact, once I began a regular regimen of resistance training, the positive shift in my mood, my confidence and my self-image was so pronounced that I switched careers.

Of course, while an anecdote about one person's experience can be compelling, it doesn't carry the same weight as a systematic observation. It's possible that the author was a biased observer of his own improvement. Therefore, we need experiments that randomly assign people to different exercise groups to test whether resistance training has a causal effect on depression and mood. 

It turns out that several researchers have, in fact, studied the effect of strength training, enough to collect and combine:  

[Dr. Jacob] Meyer was among the authors of a recent meta-analysis of the link between resistance training and depressive symptoms ... The study, published in the June 2018 issue of JAMA Psychiatry, analyzed 33 clinical trials for the effects of resistance exercise on depression. Results showed that resistance exercise “significantly reduced depressive symptoms” among research participants.

a) In your own words, what does a meta-analysis do?

b) In the meta-analysis described in the paragraph above, there were 33 studies, all of which were experiments. Given the context, what was the independent variable in each of these 33 studies? What was the dependent variable? 

c) Reread the description above, which states that strength training "significantly reduced depressive symptoms". This phrasing does not indicate the meta-analytic effect size (that is, the effect size they obtained by averaging the effect sizes of all 33 studies). To see that effect size, you'd have to turn to the original empirical article, here.  The article is open-access and the forest plot you will find there depicts  the mean, or overall, effect. What is the overall effect size? 

The meta-analysis above showed that strength training can help improve depression. What about a related mental health condition, anxiety? Turns out there's a separate meta-analysis on that:

Resistance exercise doesn’t affect depression alone; research shows that it can reduce symptoms of anxiety, too. For a 2017 study published in the journal Sports Medicine, Gordon and his colleagues conducted another meta-analysis of 16 studies involving 992 total participants; it concluded that resistance training “significantly improves anxiety symptoms among both healthy participants and participants with a physical or mental illness.”

d) How many studies were in this meta-analysis on strength training and anxiety? Estimate how many participants were in each study.

e) What would have been the independent variable in each of these studies? What would have been the dependent variable?

f) Once again, the journalist explains that resistance training "significantly improves" anxiety symptoms, but we don't hear about the effect size. The original empirical article  is behind a paywall. You might be able to access it from your own library. If you can't find it, I'll tell you that the mean effect size (d) of the studies was 0.31, 95% CI [0.17, 0.44]. What information do you need to evaluate this effect size? Is the effect strong or weak? 

As a bonus, the researchers are exploring why strength training might improve depression and anxiety. That is, they are exploring potential mediators of the relationship between strength training and mental health. Here is the first of two mediator explanations, as summarized by the journalist:

One notable finding was that participants showed an improvement in their mood regardless of whether they grew physically stronger from the exercises. ... “Perhaps it might be the sense of accomplishment and confidence that comes from exercising, rather than the achievement of actual strength gains, to explain why study subjects felt better,” Meyer says.

And the second:

Resistance training, like other exercise, induces the release of a protein called BDNF, or brain-derived neurotrophic factor, into the hippocampus region of the brain. Among other functions, the hippocampus is responsible for mood regulation, and in people who are depressed, it shrinks up to 25 percent of its normal volume. The release of BDNF triggers the growth of new brain cells in the hippocampus, restoring it to its full size and improving communication between cells.

“That’s the physiological theory behind why you feel so good after working out,” says Jason Sawyer, an assistant professor of wellness and exercise science at Rhode Island College in Providence.... 

g) Choose one of the mediator descriptions above and sketch a figure depicting the mediator argument. Use a box for each variable, and arrange the boxes in a triangle shape, using the figures at the end of Chapter 9 as a model. 

 

Selected answers

c) The overall (meta-analytic) effect size was d = 0.66 95% CI [0.48, 0.83]. Therefore, strength training groups scored about 2/3 of a standard deviation better than control groups, on average. To evaluate how strong this effect is, it might be helpful to compare the effect of strength training to some other treatments for depression, including cognitive-behavioral therapy or medication. (A 2013 meta-analysis found that CBT's effect on depression is at least d = 0.53, 95% CI [0.43, 0.62].)

d) There were 16 studies and a total of 992 participants, so that's about 165 participants per study. 

e) Each study would have used exercise condition as an IV and anxiety level as a DV. 

f) As you can see, the overall (meta-analytic) effect size of resistance training on anxiety was not as strong as the overall effect size of resistance training on depression (the two CIs do not overlap). This pattern suggests that strength training does more for depression than for anxiety. 

g) Here's how you might sketch one of these mediation proposals:

[strength training condition] -->  [sense of accomplishment] --> [improved mood]