Domain	Major flaws	Moderate Flaws	Indeterminate Flaws
Methods for selecting participants	(More than 25% of sample lost to follow up and missing records were exclusion criteria for the current review.)	≥15% of the population lost to follow up or missing records Restricted sampling, resulting in limited generalizability The study sampled from high-risk patients on a risk-assessment scale and then included the factors in the scale as potential predictor variables; or, very restricted sampling frame that resulted in limited generalizability	Inclusion/exclusion criteria are unclear
Statistical methods and control of confounding	Clearly incorrect statistical methods Inadequate number of events (pressure ulcers) for analysis: <10 pressure ulcers per variable included in the multivariate analysis10,43	Nonindependent factors are included in analysis without appropriate adjustment10 Time-dependent covariates (e.g., blood pressure) included without appropriate adjustment10 Selective reporting of results9 Inappropriate strategy for model building3 Unclear statistical reporting: Multivariate statistical significance is only reported for variables deemed significant (for underpowered studies, it is not possible to tell which variables were close and may be significant if the study was adequately powered) Despite the presence of missing data, the authors do not describe how missing data were handled Problematic statistical methods: Poor model fit or no reporting of model fit Significance tests for predictors not reported	Unclear statistical reporting
Methods for measuring exposure	Temporal ambiguity: it is possible that the predictor variable occurred after the pressure ulcer event.	Variable operationalization is unclear or misleading. Incomplete data for predictor variables Despite the presence of missing data, no description of how missing data were handled; or missing data were handled inappropriately	No reporting of missing data for predictor variables despite high likelihood of missing data
Methods for measuring outcome variable	No criteria for wound designation as a pressure ulcer (e.g., NPUAP/EPUAP ≥category 1 or equivalent)	Nurses who were not wound nurses and not specially trained identified or categorized pressure ulcers.	Limited description of the outcome variable (e.g., no staging information)
Conflict of interest	Evidence of conflict of interest, with major implications for study results	Evidence of conflict of interest, with minor implications for study results	Evidence of conflict of interest, with unclear implications for study results

References:

⁹Coleman S, Gorecki C, Nelson EA, et al. Patient risk factors for pressure ulcer development: systematic review. Int J Nurs Stud. 2013;50(7):974–1003. doi:10.1016/j.ijnurstu.2012.11.019.

¹⁰Harrell FE. Regression modeling strategies. New York, NY: Springer; 2001.

⁴³Peduzzi PJ, Concato AR, Feinstein X, Holford TR. Importance of events per independent variable in proportional hazards regression analysis. II. Accuracy and precision of regression estimates. J Clin Epidemiol. 1996;48(12):1503–1510.