RealRisk

You’ve described the baseline or control condition as ‘insert condition in baseline group’

Now, you need to find out the absolute risk of the outcome in that control or baseline group – the

baseline risk.

This is the trickiest step.

Usually a percentage of people who experienced some outcome.

Here are some examples:

- If the study is investigating HRT and breast cancer, you need to find the risk of developing breast cancer amongst the group of women who

weren’t

taking HRT.

- If the study is investigating saturated fat and heart disease, you need to find the risk of developing heart disease amongst the group eating the

least

amount of fat.

- If the study is investigating a new antidepressant drug and depression, you need to find the rate of depression amongst the group taking the

placebo

or the

old

antidepressant.

- Check the paper. You are looking for a percentage or a proportion e.g. “10% of those not taking HRT developed breast cancer”. Sometimes you can calculate the percentage yourself, if the raw numbers are reported.

- If it’s not in the paper, request it from the corresponding author. Click

here

for guidance.

- Find a relevant figure from a trustworthy authority. Click

here

for guidance.

Baseline Risk

The ‘baseline risk’ is a percentage or proportion. It tells you the number of people in the baseline group who developed some particular outcome.

For example, if 200 out of 1000 people in the control or baseline group received a diagnosis of cancer during the study, the baseline risk for cancer in that group was (200/1000 x 100) = 20%.

Absolute Risk

The ‘baseline risk’ is a percentage or proportion. It tells you the number of people in the baseline group who developed some particular outcome.

For example, if 200 out of 1000 people in the control or baseline group received a diagnosis of cancer during the study, the baseline risk for cancer in that group was (200/1000 x 100) = 20%.

The absolute risk is not in the paper. What can I do?

• Contact the corresponding author and request it. Remember, if their study reports an RR, OR or HR they are explicitly comparing outcomes between two groups. You are just asking for the risk (or probability) of the outcome in one of those groups - the control or baseline. (You could even ask them to fill out RealRisk themselves!)

Researchers may point out that these numbers sometimes come out of statistical models, and don’t emerge straightforwardly from the raw numbers. That is true, but don’t be fobbed off - they can still calculate the baseline risk!

• If the corresponding author is unhelpful, you may have to look elsewhere for a relevant statistic. Charities like

Cancer Research

Mind

Rare Disease UK

etc. may be able to help, and their websites often include the relevant facts and figures. Other useful organisations include the

World Health Organisation

, the

CDC

for US stats, and the

NHS

ONS

for the UK.

If you are a journalist looking to report a piece of research, note that you

don’t

have to use exactly the same baseline risk as the one used in the paper.

For example, if a piece of research reports a 70% increased risk (an RR of 1.7) of depression amongst under 18s year olds who vape, you could quote a trusted authority on the percentage of under 18s who suffer from depression – and then apply the 70% increase to that. It may not be the exact baseline figure used in the study, but if it’s a trustworthy number with direct relevance to your audience, it’s a correct and effective way to report the research.

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Baseline Risk

Results summary