Randomised control trials represent one of the best ways to test out new treatments and are essential for AKT questions.

The advantages of RCTs are as follows:
Unbiased
Blinding of participant (single)
Blinding of researchers (double)
More powerful statistical analysis

Disadvantages:
Expensive
Time-consuming
Ethical issues (leading to permission needed… more time… etc etc)

From RCTs you can calculate several aspects:

Absolute risk (AR)
Absolute risk (AR) is the chance (or actual) risk of developing a condition, with zero meaning NO risk.

Absolute risk reduction (ARR)
DIFFERENCE between the control and intervention.
So your control group will be your baseline.
Can be Absolute risk increase (ARI)

Control event rate (CER) is the measure of how often the event happened in the control group
Experimental event rate (EER) is how often that event occurred in the experimental group (who have the intervention.

ARR or ARI = CER - EER

Numbers needed to treat (NTT)
So depending on the result can calculate the rate by the inverse of the ARR
NNT = 1 / ARR
NNT = 1 / CER – EER

Numbers needed to harm (NNH)
Can be calculated using the inverse of the ARI.
NNH = 1 / ARI
NNH = 1 / CER – EER

A Cates plot can be used then to give some of the information that we can use.

I hope that you find that useful

Chapters:
00:00 Introduction
00:16 Overview
00:45 Advantages and disadvantages of RCT
01:50 Absolute risk
02:24 Control Event Rate and Experimental Event Rate
03:24 Question example - ARR
03:51 Question example - ARI
04:32 Question example - NNT
05:14 Calculating relative risk reduction
05:56 Question example - NNH
06:29 Question example - Cates plot

Dr David Hindmarsh
gptemplates@gmail.com

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