# Questions tagged [risk-difference]

The risk-difference is the difference between the probabilities of an event under two conditions (ie, p1-p2). The RD has a possible range of [-1, 1]. It is a common measure of effect size in biomedical research.

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### What are the issues with absolute risk reduction/relative risk reduction vs odds ratios in reference to variation over risk factors

The following quote is from this: Any measure that has the potential for summarizing a treatment effect with one constant for all types of patients will be non-collapsible when the outcome is ...
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### Is the mean difference between two groups a relative treatment effect?

In randomized trials, I know that treatment effects such as the odds ratios, relative risks and hazard ratios are considered relative treatment effects. What about the following effect sizes? a. Mean ...
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### Inconsistent risk difference confidence interval and pvalue from Chi2-test

I am using the svyglm function in the survey package in R to compute a risk difference in proportions, 95% confidence interval and p-value. The outcome is binary ...
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### Strange formulas for binary outcomes in meta-analysis

I am reading the book: Shahjahan Khan. Meta-Analysis Methods for Health and Experimental Studies. Springer 2020. https://link.springer.com/book/10.1007/978-981-15-5032-4 On page 23, there are formulas ...
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### Use of $p_1/(p_1+p_2)$ to compare two probabilities $p_1$, $p_2$?

Let's say we want to compare two probabilities $p_1$ and $p_2$, not necessarily referred to the same population. For example, $p_1$ may be the probability of getting a certain disease conditioned on ...
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1 vote
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### Adjusted risk difference and negative confidence interval

I was reading this article. The authors used mixed effects logistic regression and presented their results as adjusted risk difference. I noticed that some of the confidence interval were negative, I ...
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### How can I estimate the risk difference confidence interval with the standard errors of the risks?

I have two risks estimated from imputed data, so I cannot say I have a1 events in the exposed and a0 events in the unexposed, as each data set is different. The output of the function are risks and ...
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1 vote
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### Risk difference with patient-years incidence rates

I am aware that you can compute risk differences as the difference of risk between two treatment arms $( (\text{No. events}_1/ N_1) - (\text{No. events}_2 / N_2))$. However, can I estimate the same ...
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### Bootstrap for random effects logistic regression to get CI for difference in proportions

Let's say I have two observations of a binary variable per patient on two different treatments for a sensible number of patients, some variable like age, and I'm fitting a model like this in R: ...
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### Calculating risk difference with covariate

How do I calculate a risk difference for a binary outcome that takes into account a covariate? I want to compare accuracy of a skilled and unskilled tester at detecting 7 different types of tumors. ...
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1 vote
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### Is there a minimum variance for metafor::rma.mv()?

I want to run a three-level meta-analysis model of observed data with Measurement as a nested level of Study (independent samples, only source of covariance being the study group measuring them) using ...
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### Calculating risk difference and number needed to treat from hazard ratio in meta-analysis

If you have primary data, there exist several ways to calculate a risk difference (RD) or number needed to treat (NNT) from time-to-event data (see e.g. following pmid: 29955580, 31626655). However, I ...
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### In a meta-analysis, can you back calculate estimated group proportions from risk difference?

In a meta-analysis of the risk difference, does it make sense to apply the weights & back calculate the expected proportions in each group? For example, if you had the following: ...
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### What's "the clinically important absolute scale"?

In this article, the authors used the sentence "...risk difference (i.e., treatment effect on the clinically important absolute scale)". What did they mean by "clinically important ...
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### Odds Ratio Vs. Risk Ratio

Relative risk, odds ratio, risk ratio, risk difference - these are all measures of the direction and the strength of the association between two categorical variables. Can I use any of these four ...
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### Is there any better alternative to Linear Probability Model?

I read here, here, here, and elsewhere that linear probability model (LPM) might be used to get risk differences when the outcome variable is binomial. LPM has some advantages such as ease of ...
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### Is there a two-by-two contingency table dataset where an Odds Ratio estimate would work and a Risk Ratio would fail?

I am wondering if there is an example of a two-by-two contingency table dataset where an Odds Ratio estimate would work and a Risk Ratio would fail, or vice versa? In additional are there cases where ...
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### Using patient characteristics to predict disease and confront with per hospital real cases

We have a large, nationwide prevalence study about the prevalence of healthcare-associated infections (HAI). We need to see if hospitals have more or less HAI than expected by their patients' ...
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### Correct model for comparing frequencies of comorbidities, large numbers

Here is what my group wants to do: Query a database for cases of several disorders, including Disorder A and Disorder B. Of those cases, specifically query for cases of Disorder A comorbid with each ...
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1 vote
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### Why do we use the equal-means assumption in estimating the SE in a z-test but not a t-test?

When we perform a z-test for the difference in proportions between two groups of binary data, we use the fact that under the null hypothesis the proportions are assumed equal in order to estimate the ...
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1 vote
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### Absolute risk and NNT from logistic regression

I fitted a Logistic regression with a number of variables, and was asked about the absolute risk (AR) and number needed to treat (NNT) for one of the variable with the outcome. I understand how to ...
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Assume that two drugs were tested. The risk of death for drug 1 is $p_1$ and the risk for drug 2 is $p_2$. We define: Risk difference (RD) $RD=p_1-p_2$ The number needed to treat (NNT) $NNT=1/|RD|$ ...