# Indirect Relative Risk Adjustment (IRRAD)

### Description

IRRAD is an Excel spreadsheet that extends the “Axelson adjustment” for binary variables to adjust observed RRs for a (measured or unmeasured) confounding variable when exposure and confounder have multiple categories. IRRAD allows the User to designate a multiplicative or an additive relative risk (RR) model for the joint association of exposure (X) and confounder (C). Additionally, the spreadsheet solves linear equations to define those characteristics that a confounder must have to explain fully or partially an observed association.

- License Agreement
- IndirectRRAdjustment(IRRAD)_NCI_DCEG_ 2018_v1.3.xlsm
- Note: End users will need to enable macros, which are used throughout to create an interactive user interface. All calculations however, are done within the excel worksheets.
*Updated: December, 2018*

- Note: End users will need to enable macros, which are used throughout to create an interactive user interface. All calculations however, are done within the excel worksheets.

### Details

The spreadsheet incorporates four approaches to assess confounder effects under either a multiplicative or additive model. These include:

**Binary exposure and binary confounder**: a) find the adjusted RR given the observed RR, P(C=1|X=1) and P(C=1|X=0) [or equivalently the observed RR, P(C=1|X=0) and the odds ratio OR(X,C)]; and b) solve for the necessary OR(X,C) given the observed, adjusted and confounder RRs and P(C=1|X=0);**Categorical exposure and categorical confounder**: find the adjusted RRs for each level of exposure given the observed RRs, the confounder distribution at each level of exposure P(C|X) and confounder RRs at the reference level of exposure;**Categorical exposure and binary confounder**: solve for the conditional distribution of the confounder at each level of X, P(C=1|X), given the observed, adjusted and confounder RRs and P(C=1|X=0);**Categorical exposure and catgorical confounder**: solve for the confounder RRs given the observed RRs, the adjusted RRs and P(C|X).

IRRAD includes the data used for the examples in Lubin et al.

### Support

Email: Contact DCEG

### Reference

- Lubin JH, Hauptmann M, Blair A. Indirect adjustment of relative risks of an exposure with multiple categories for an unmeasured confounder.
*Ann Epidemiol*2018

**Note**: IRRAD is currently under review and development for 508-compliance.