What is nnt and nnh

So, how many patients will need to be treated for there to be 1 extra responder? By a simple mental calculation, we determine that 7. Antidepressant treatment resulted in 11 extra responders for every subjects treated.

NNTs are calculated only when response rates are available. The NNT is not limited to response rates; it can be estimated for remission rates, as well. For example, in a meta-analysis of RCTs of aripiprazole versus placebo for acute mania, the NNT was 6 for response and 14 for remission. The NNT is not limited to comparisons with placebo; it can be estimated for comparisons with an active control, as well. What is the importance of the value of the NNT?

Obviously, the smaller the NNT, the greater the unique contribution of the drug toward the outcome. So, if the NNT for a drug is 4, it means that just 4 patients need to be treated with that drug for 1 additional patient to respond; in contrast, if the NNT is 18, it means that as many as 18 patients need to receive the drug for 1 additional patient to respond.

Note that the NNT cannot lie between 0 and 1; it is impossible, for example, for half a patient to be treated for 1 additional patient to respond. The highest possible value for NNT is infinity; this is when the response rate is the same in treatment and control groups.

Or should we reject a drug if it is associated with a high NNT? Not necessarily. Consider the following situations:. In passing, it may be noted that it is easier to demonstrate statistical significance when comparing active drug with placebo than when comparing active drug with an active control. This is why the NNT is higher in the latter situation. The larger the margin of separation between 2 treatments, the smaller the value of the NNT. For example, in week trials of levomilnacipran for major depressive disorder, the NNTs for response and remission were 9 and 14, respectively, and the NNHs for different adverse effects ranged from 10 to 31; the NNH for dropout due to adverse events was Clinicians need to make a subjective judgment about the value of the benefit and the seriousness of the risk.

Even though the blood dyscrasia is far less likely to occur than pain relief, the seriousness of the dyscrasia would certainly discourage the clinician from prescribing the drug. The NNT is an academically useful statistic, but it has limited value for the practicing clinician. This section explains why. If the NNT is, say, 9, we understand that 9 patients will need to receive the treatment for 1 extra patient to respond. We do not know how many patients will respond anyway because of placebo-related mechanisms, nor do we know how many patients will not respond at all.

To obtain this information, we need to return to the data from which the NNT was calculated. Now, here is something interesting. These 2 situations are strikingly different. In the first situation, there is almost no placebo response, and medication is associated with a relatively large treatment gain.

In the second situation, there is a large placebo response, and medication is associated with a relatively small treatment gain. Yet, the NNT is the same in the 2 situations. So, it is really important for clinicians to know not only what the unique contribution of the drug is NNT but also what the placebo response and nonresponse rates are. Readers may also note that the NNT is a crude measure. This is because it is based on the response rate, which is also a crude measure.

Thus, a lot of information is lost when outcomes are dichotomized into response and nonresponse categories. With regard to adverse events, these may happen or not; in such situations, adverse event rates in drug and placebo groups and the NNH value are appropriate estimates.

The occurrence of nausea as an adverse effect of serotonin reuptake inhibitors is a case in point. However, if outcomes can be quantified, then additional information can be clinically useful. For example, it could be helpful to know the NNH for the occurrence of akathisia with aripiprazole, but it could also be helpful to know by what margin akathisia is rated as more severe with aripiprazole as compared with placebo.

Limitations of the NNT have also been discussed by Hutton. Very surprisingly, almost nobody who cites an NNT value mentions the time frame for that value. Study findings showed a 0.

That means people would need to be scanned — and exposed to radiation, and potentially other harms from biopsies and follow-up procedures — in order to prevent one lung cancer death. But that was the relative risk reduction RRR.

The absolute risk reduction was actually 1. Many studies show that communicating risk information in only relative terms usually misleads patients into overestimating the benefits of therapies.

There also has been some work showing that using NNT alone can be misinterpreted by patients. Hilda Bastian, PhD is a research scientist, blogger, and cartoonist who thinks the NNT is not an intuitive statistical concept to grasp.

Others point out that interventions with a high NNT can deliver important public health benefits. In the Lipitor example above, for example, although 1 out of chances might not be favorable odds for any individual patient, the cumulative impact of the drug across a population of millions may still be substantial.

For those who want to learn more about other limitations of the NNT, try this article from the Journal of the Canadian Medical Association. Please note , comments are no longer published through this website. All previously made comments are still archived and available for viewing through select posts. This is a wonderful article but some of the English is muddled as it often is when dealing with relative risk. Consider this from the article:.

Or, relative risk reduction is absolute risk reduction divided by placebo risk. We welcome comments, which users can leave at the end of any of our systematic story reviews or at the end of any of our blog posts. This site is primarily a forum for discussion about the quality or lack thereof in journalism or other media messages advertising, marketing, public relations, medical journals, etc. It is not intended to be a forum for definitive discussions about medicine or science.

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