Well, duh — life experiences up to middle age make a difference in establishing psychological baselines for anxiety and depression in a (tiny ?) sample of identical twins

Perhaps trivial evidence for what common sense already thought it knew

Even with near-identical genetics (insofar as we can eliminate pre-existing epigenetic variances), life experience matters in regard to establishing habitual outlooks:

Our life experiences – the ups and downs, and everything in between – shape us, stay with us and influence our emotional set point as adults, according to a new study led by Virginia Commonwealth University researchers.

The study suggests that, in addition to our genes, our life experiences are important influences on our levels of anxiety and depression.

© 2011 Sathya Achia Abraham, VCU Study: We Are What We Experience, Virginia Commonwealth University – Communications and Public Relations (05 October 2011) (paragraph split)

Citation

Kenneth S. Kendler, Lindon J. Eaves, Erik K. Loken, Nancy L. Pedersen, Christel M. Middeldorp, Chandra Reynolds, Dorret Boomsma, Paul Lichtenstein, Judy Silberg, and Charles O. Gardner, The Impact of Environmental Experiences on Symptoms of Anxiety and Depression Across the Life Span, Psychological Science 22(10): 1343-1352 (October 2011)

Sample size is unclear in the paper’s abstract

Either bad science or bad writing:

To address this question, we analyzed longitudinally assessed symptoms of anxiety and depression in eight samples of monozygotic twins of widely varying ages. These samples were drawn from American and European population-based registries.

© 2011 Kenneth S. Kendler, Lindon J. Eaves, Erik K. Loken, Nancy L. Pedersen, Christel M. Middeldorp, Chandra Reynolds, Dorret Boomsma, Paul Lichtenstein, Judy Silberg, and Charles O. Gardner, The Impact of Environmental Experiences on Symptoms of Anxiety and Depression Across the Life Span, Psychological Science 22(10): 1343-1352 (October 2011) (from the abstract)

Are we talking 16 people here, from an alleged plethora of cultures?  Or is “sample” meant to express larger numbers of twin-pairs from varying cultures?

The first is bad science.  The second is bad communication.

Method

If we’re talking only 16 people, the following method is nonsense:

Using hierarchical linear modeling, we examined individual differences and individual changes in the level of symptoms over time.

This method enabled us to decompose the variance into the predictable variance shared by both members of each pair of twins, the differences between individuals within pairs, and the residual variance. We then modeled how these components of individual variation changed over time.

© 2011 Kenneth S. Kendler, Lindon J. Eaves, Erik K. Loken, Nancy L. Pedersen, Christel M. Middeldorp, Chandra Reynolds, Dorret Boomsma, Paul Lichtenstein, Judy Silberg, and Charles O. Gardner, The Impact of Environmental Experiences on Symptoms of Anxiety and Depression Across the Life Span, Psychological Science 22(10): 1343-1352 (October 2011) (from the abstract) (paragraph split)

Results

These, at least, were clearly stated:

Within pairs, the twins’ predicted levels of symptoms increasingly diverged from childhood until late adulthood, at which point the divergence ceased. By middle adulthood, environmental experiences contributed substantially to stable and predictable interindividual differences in levels of anxiety and depression.

© 2011 Kenneth S. Kendler, Lindon J. Eaves, Erik K. Loken, Nancy L. Pedersen, Christel M. Middeldorp, Chandra Reynolds, Dorret Boomsma, Paul Lichtenstein, Judy Silberg, and Charles O. Gardner, The Impact of Environmental Experiences on Symptoms of Anxiety and Depression Across the Life Span, Psychological Science 22(10): 1343-1352 (October 2011) (from the abstract) (paragraph split)

I suppose I could have paid for the article and learned the sample size — but why?

If a purported research team can’t be bothered to be accurate and reasonably precise in its abstract, its paper is arguably not worth my time or money.

Why?  Because an equal lack of clarity is likely to show up in the body of the paper.

That Psychological Science would publish such a poor abstract does not reflect well on its standards and/or editorship.