# What is risk difference in meta-analysis?

Table of Contents

## What is risk difference in meta-analysis?

The risk difference is the difference between the observed risks (proportions of individuals with the outcome of interest) in the two groups (see Box 9.2. a). The risk difference can be calculated for any study, even when there are no events in either group.

## How do you calculate absolute risk difference?

How to calculate risk

- AR (absolute risk) = the number of events (good or bad) in treated or control groups, divided by the number of people in that group.
- ARC = the AR of events in the control group.
- ART = the AR of events in the treatment group.
- ARR (absolute risk reduction) = ARC – ART.
- RR (relative risk) = ART / ARC.

## What is NNT in meta-analysis?

The calculation of NNT (number needed to treat) in meta-analysis is described using RR and OR, which are more robust against variability in baseline risk. As we all know, NNT is an absolute measure of effect that is used to estimate the efficacy or safety of an intervention.

## Can you calculate NNT with meta-analysis?

Calculating the number needed to treat (NNT) The NNT can be obtained directly from a meta-analysis that pools risk differences from several trials.

## When would you use a meta-analysis?

Meta-analysis should be conducted when a group of studies is sufficiently homogeneous in terms of subjects involved, interventions, and outcomes to provide a meaningful summary. However, it is often appropriate to take a broader perspective in a meta-analysis than in a single clinical trial.

## How do you interpret meta-analysis results?

To interpret a meta-analysis, the reader needs to understand several concepts, including effect size, heterogeneity, the model used to conduct the meta-analysis, and the forest plot, a graphical representation of the meta-analysis.

## What is absolute risk in statistics?

Absolute risk is always written as a percentage. It is the ratio of people who have a medical event compared to all of the people who could have an event. For example, if 26 out of 100 people will get dementia in their lifetime, the absolute risk is 26/100 or 26%.

## What does absolute risk measure?

ABSOLUTE MEASURES OF RISK. Risk can also be expressed in absolute terms by means of the absolute risk difference (synonym: attributable risk). This absolute measure of effect represents the difference between the risks in two groups; usually between an exposed and an unexposed group (Box 1).

## What is a good NNT number?

1

The ideal NNT is 1, where everyone improves with treatment and no one improves with control. A higher NNT indicates that treatment is less effective. NNT is similar to number needed to harm (NNH), where NNT usually refers to a therapeutic intervention and NNH to a detrimental effect or risk factor.

## What is a reasonable NNT?

As a general rule of thumb, an NNT of 5 or under for treating a symptomatic condition is usually considered to be acceptable and in some cases even NNTs below 10. Below are some NNTs for routine medical interventions.

## How do you calculate number needed to treat in meta analysis?

Calculating numbers needed to treat The number needed to treat is the reciprocal of the absolute risk difference for a bad outcome between treated subjects and the control or placebo group—that is, 1÷(risk of bad outcome in placebo group−risk of bad outcome in treated group).

## How do you calculate number needed to treat?

NNTs are always rounded up to the nearest whole number and accompanied as standard by the 95% confidence interval. Example: if a drug reduces the risk of a bad outcome from 50% to 40%, the ARR = 0.5 – 0.4 = 0.1. Therefore, the NNT = 1/ARR = 10. The ideal NNT would be 1 – ie all patients treated will benefit.

## When to use StatsDirect in a meta-analysis?

Meta-analysis may be used to investigate the combination or interaction of a group of independent studies, for example a series of fourfold tables from similar studies conducted at different centres. This StatsDirect function examines the risk difference within each stratum (a single fourfold table) and across all of the studies/strata.

## Which is the best example of absolute risk?

In healthcare, risk refers to the probability of a bad outcomein people with the disease. Absolute riskreduction (ARR) – also called risk difference (RD) – is the most useful way of presenting research results to help your decision-making. In this example, the ARR is 8 per cent (20 per cent – 12 per cent = 8 per cent).

## Which is an example of an absolute measure?

Absolute measures, such as the risk difference, are particularly useful when considering trade-offs between likely benefits and likely harms of an intervention. The risk difference is naturally constrained (like the risk ratio), which may create difficulties when applying results to other patient groups and settings.

## What is the risk difference in a study?

The risk difference is the difference between the observed risks (proportions of individuals with the outcome of interest) in the two groups (see ). The risk difference can be calculated for any study, even when there are no events in either group.