Experimental event rate

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In epidemiology and biostatistics, the experimental event rate (EER) is a measure of how often a particular statistical event (such as response to a drug, adverse event or death) occurs within the experimental group (non-control group) of an experiment. [1]

Contents

This value is very useful in determining the therapeutic benefit or risk to patients in experimental groups, in comparison to patients in placebo or traditionally treated control groups.[ citation needed ]

Three statistical terms rely on EER for their calculation: absolute risk reduction, relative risk reduction and number needed to treat.

Control event rate

The control event rate (CER) is identical to the experimental event rate except that is measured within the scientific control group of an experiment. [2]

Worked example

In a trial of hypothetical drug "X" where we are measuring event "Z", we have two groups. Our control group (25 people) is given a placebo, and the experimental group (25 people) is given drug "X".

Event "Z" in control group : 4 in 25 people Control event rate  : 4/25

Event "Z" in experimental group : 12 in 25 people Experimental event rate : 12/25

Another worked example is as follows:

 Example 1: risk reductionExample 2: risk increase
Experimental group (E) Control group (C)Total(E)(C)Total
Events (E)EE = 15CE = 100115EE = 75CE = 100175
Non-events (N)EN = 135CN = 150285EN = 75CN = 150225
Total subjects (S)ES = EE + EN = 150CS = CE + CN = 250400ES = 150CS = 250400
Event rate (ER) EER = EE / ES = 0.1, or 10% CER = CE / CS = 0.4, or 40%EER = 0.5 (50%)CER = 0.4 (40%)
EquationVariable Abbr. Example 1Example 2
EER CER< 0: absolute risk reduction ARR()0.3, or ()30%N/A
> 0: absolute risk increaseARIN/A0.1, or 10%
(EER CER) / CER< 0: relative risk reduction RRR()0.75, or ()75%N/A
> 0: relative risk increaseRRIN/A0.25, or 25%
1 / (EER CER)< 0: number needed to treat NNT()3.33N/A
> 0: number needed to harm NNHN/A10
EER / CER relative risk RR0.251.25
(EE / EN) / (CE / CN) odds ratio OR0.1671.5
EER CER attributable risk AR()0.30, or ()30%0.1, or 10%
(RR 1) / RR attributable risk percent ARPN/A20%
1 RR (or 1 OR) preventive fraction PF0.75, or 75%N/A

See also

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References

  1. "Experimental event rate (EER)". www.medicine.ox.ac.uk. Archived from the original on 20 August 2010. Retrieved 22 May 2022.
  2. "Control event rate (CER)". www.medicine.ox.ac.uk. Archived from the original on 20 August 2010. Retrieved 22 May 2022.