# 27 Nov How to perform a multivariable analysis

Several steps are necessary to perform a multivariable (multivariate) analysis:

- Formalizing the research hypothesis
- Select the outcome variable Y
- Select the explanatory variables X

- Identify covariates
- Check that the conditions are met
- Check the robustness of the model

## Formalizing the research hypothesis

All research requires hypotheses to be made. For example, it may be: “Does our new service protocol reduce the number of readmissions?”. Sometimes this hypothesis is straightforward to explain, sometimes it is more complex.

pvalue.io helps you to formalize it, by assuming the following: “X has an influence on Y”. It is up to you to determine the relevant X and Y. In the example on readmissions, X would be: the service protocol (coded for example in 2 classes: “former” and “new”), and Y the presence of a 30-day readmission (e. g. yes/no or 0/1). The hypothesis would therefore be: “The service protocol has an influence on 30-day readmission”.

However, there are many possible biases, so it is often necessary to use covariates. These covariates are the variables related to Y.

## Identify adjustment variables

Thus, pvalue.io first prompts you to select the variables known or assumed to be related to Y. Then, it automatically selects the covariates not known related to Y. Typically, we do not need to obtain the estimate of the influence of these variables. If these variables are numerical, a natural cubic spline transformation is performed.

## Check that the conditions are met

This verification step is essential and uses automatic detection mechanisms (for example, the residuals normality check), or manual (for example, checking the linearity of X as a function of Y, or proportional hazards).

## Check the robustness of the model

After a multivariable analysis, it is necessary to check the robustness of the model by removing the most influential variables from the statistical model. This procedure has not yet been implemented.

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