- A mood-based personality construct was created to combine the common symptoms of anxiety and depression 
- Negative affectivity includes features of the two disorders; positive affectivity the disorders separate 
- Depression involves a combination of high negative affectivity and low positive affectivity; anxiety involves high negative affectivity with "positive affectivity failing to play a salient role"
- High NA is common to anxiety and depression, low PA is unique to depression
- NA and PA are good constructs in helping us understand the distinct and overlapping symptoms of anxiety and depression

Indiana University

There are theoretical and definitional issues with the comorbidity of Anxiety and Depression such as: 
- Symptoms Versus Syndromes
- Single Construct: Negative Affectivity
- Temporality
- Heterogeneity

Theoretical and Definitional Issues

Kendall, P. C., Kortlander, E., Chansky, T. E., &amp; Brady, E. U. (1992). Comorbidity of anxiety and depression in youth: Treatment implications. Journal of Consulting and Clinical Psychology, 60(6), 869–880. https://doi.org/10.1037/0022-006x.60.6.869 

Comorbidity of Anxiety and Depression in Youth: Treatment Implications

- Anxiety and depression symptoms can seem very similar and overlap
- It is important to differentiate "anxietylike" and "depressionlike" symptoms from indicators of the syndromal disorder
- If we were to go based off of the presence of symptoms rather than the presence of the disorder, rates of comorbidity would be inflated as a result

Symptoms Versus Syndromes

Single Construct: Negative Affectivity 

- Researchers have discussed comorbidity in the context of temporal progression and suggesting that anxiety predates depression
- Untreated anxious conditions transform into depression 
- Depression symptoms may feel more prevalent at the beginning of treatment and decrease with time, but then anxious symptomology emerges  

Temporality

- It is important not only to acknowledge the overlap and commonalities of the symptoms of anxiety and depression, but it is just as important to observe the heterogeneity within and between types of anxiety and depression disorders 
- Treatment and therapeutic approaches vary based on individual cases by looking at their diagnostic symptoms and disorders

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