Assignment: Find any article using clustered data and describe:
Article: Carra G, Crocamo C, Borrelli P, Tabacchi T, Bartoli F, Popa I, et al. Area-level deprivation and adverse consequences in people with substance use disorders: findings from the Psychiatric and Addictive Dual Disorder in Italy (PADDI) Study. Sub Use & Misuse, 52:4, 451-458. DOI: 10.1080/10826084.2016.1240696.
1. The unit of clustering
The authors were interested in examining the effects of geographic area-level factors on overdose, HCV, HBV, and long-term incarceration at the individual level. They explored both individual-level (level 1) and geographic area-level (level 2) data. The purpose was to explore the effects that contextualization characteristics may have on health at an individual level, even after accounting for individual level variation. The authors’ used data from a national survey (Psychiatric and Addictive Dual Disorder) and the national census track.
2. The hypothesized effect and level at which the exposure is measured (is it a characteristic of the cluster or the observation within the cluster)
Hypothesized effect: The authors hypothesized that among people with substance use disorders, area-level deprivation would be significantly associated with overdose, HCV, HBV, and long-term incarceration beyond what would be expected from individual level data. The exposure variables (measurements of geographic level deprivation based on aggregate census data) was measured as a characteristic of the area-level cluster. Deprivation was measured based on five census track markers at the census block level: low level of education, unemployment, non-home ownership, one parent family, and overcrowding – the index is calculated by summing standardized indicators, which then corresponds to four area levels of deprivation: very deprived, deprived, intermediate, affluent and very affluent. The same approach is applied to aggregate data at the municipality level. Because of a small sample size for this study, the authors combined levels into three overall area-level categories: affluent, intermediate and deprived.
3. The statistical model used to estimate the effect
Due to small sample size (small number of subjects (level 1) per area level context (level 2)), the authors did not use a multilevel analysis. Instead, they fitted a logistic regression model with cluster-robust error for each outcome, modeling individual-level and geographic area-level effects. They included identified predictors as covariates and used a likelihood ratio test to compare nested models to examine the effect that different variables had on the regression equations.
4. Describe whether there are any other statistical models that might be appropriate and whether they would be preferable (e.g., GEE vs. mixed).
It wouldn’t have been appropriate to use multilevel modeling in this instance due to the low sample size. However, due to the sample size, I’m really not sure what other statistical methods would have been appropriate for the analysis. Suggestions??