Number of treatments required

from Wikipedia, the free encyclopedia
Risk indicators
absolute risk
relative risk (RR)
attributable risk (AR)
absolute risk reduction (ARR)
relative risk reduction (RRR)
number of necessary treatments (NNT)
chance
odds ratio (OR)

The number needed to treat ( english number needed to treat , in short NNT ) is a statistical measure that indicates how many patients per unit of time (eg 1 year.) Must be treated with the test substance or test method for the studied Population to achieve the desired therapy goal (e.g. to reduce the number of heart attacks by 10%). In addition to the absolute and relative risk reduction, it is a means of showing the benefit of a treatment in figures and corresponds to the reciprocal value of the absolute risk reduction (ARR). A larger NNT therefore means a smaller risk reduction per treatment.

NNT is also in the preventive medicine used and sometimes as the number of necessary screen operations (s. Numbers needed to screen, NNS), respectively.

In practice, the NNT with the NNH should ( English number needed to harm ) be related, d. That is, the number of treatments necessary to achieve the desired therapeutic goal in a patient is compared with the number of treatments necessary to cause harm to a patient.

calculation

You can illustrate the relationships with the help of a four-field table. This represents a possibility of evaluating a scientific study. Ideally, it is a prospective, controlled and randomized clinical study .

It is assumed that two possible measures lead to a certain goal with different frequency (target point). Two (patient) groups are compared that differ only in the measure used. Other influencing factors were excluded by the randomization. A standardized examination is used to determine how many patients in the respective group achieved the goal and how many failed.
Target point
reached not reached
Measure 1 A. B.
Measure 2 C. D.

It says:

  • A for the number of patients for whom the goal was achieved with measure 1,
  • B for the number of patients for whom the goal was not achieved with measure 1,
  • C for the number of patients for whom the goal was achieved with measure 2,
  • D for the number of patients for whom the goal was not achieved with measure 2.

The ARR ( Absolute Risk Reduction ) is then calculated as follows:

A positive absolute risk reduction means that measure 1 is superior to measure 2. If the absolute risk reduction has a negative value, this means that measure 1 is inferior. The confidence interval of the ARR is also important for the informative value of the ARR .

The NNT is calculated as follows:

or

A negative ARR would not be represented as a negative number needed to treat , but as a positive number needed to harm (NNH).

Rounding

Since the NNT describes a number of patients (to be treated), the information is usually rounded up to whole numbers: if the arithmetic result would be "4.2304 patients", it is stated that (at least) 5 patients must be treated, so that one patient more achieves the desired result.

Value

It is important that the values ​​of the NNT or the ARR, strictly speaking, initially only apply to the study in which they were determined. The external validity of the study describes the transferability to the outside world - that is, to a special case or to a general statement. It is therefore important that, in addition to the NNT, the groups, the period and the target point are precisely described. Example:

If male white patients between the ages of 23 and 34 who have a cold but are otherwise very healthy are treated with 5 g of drug A for seven days, 100,000 patients would have to be treated so that 1 more patient becomes cold-free after 10 days, than would have been the case without any treatment.

literature

Web links