what happens if the number needed to treat for treatment was negative

In case we are monitoring a bad outcome the number needed to treat (NNT) is negative and if we are monitoring a good outcome the NNT is positive if the difference is derived by formula Absolute Risk Reduction (ARR) = outcome event rate in treatment group-outcome event rate in placebo group. Competing interests: No competing interests

Full Answer

What is the NNT number needed to treat?

Number needed to treat. The number needed to treat ( NNT) is an epidemiological measure used in communicating the effectiveness of a health-care intervention, typically a treatment with medication. The NNT is the average number of patients who need to be treated to prevent one additional bad outcome (e.g.

What is the NNT of a drug?

If the drug or intervention is harmful the NNT will be negative. This is sometimes referred to as the ‘Number Needed to Harm’ (NNH). This can also be used to describe adverse effects, for example as a result of the treatment under study. It is important to distinguish between treatments and preventative (prophylactic) measures.

What is the number needed to harm (NNH)?

That decision is made easier by knowing the NNT. Number Needed to Harm (NNH): The number of people who, if they received the intervention in question, would lead to just one person being harmed. With NNH, instead of looking at desirable outcomes, you are comparing the absolute risk increase of bad outcomes.

How many individuals need to be treated to prevent 1 adverse outcome?

Group exposed to a treatment (left) has reduced risk of an adverse outcome (grey) compared to the unexposed group (right). 4 individuals need to be treated to prevent 1 adverse outcome (NNT = 4).

What is an acceptable number needed to treat?

As a general rule of thumb, an NNT of 5 or under for treating a symptomatic condition is usually considered to be acceptable and in some cases even NNTs below 10. Below are some NNTs for routine medical interventions. Note that the various tables below offer additional context to the numbers.

What is a bad NNT?

The ideal NNT is 1, where everyone improves with treatment and no one improves with control. A higher NNT indicates that treatment is less effective. NNT is similar to number needed to harm (NNH), where NNT usually refers to a therapeutic intervention and NNH to a detrimental effect or risk factor.

How do you interpret number needed to treat?

The Number Needed to Treat (NNT) is the number of patients you need to treat to prevent one additional bad outcome (death, stroke, etc.). For example, if a drug has an NNT of 5, it means you have to treat 5 people with the drug to prevent one additional bad outcome.

What does a negative number needed to harm mean?

A negative NNH means that a patient assigned to the comparator (placebo) has a lower risk for the adverse event of interest than a patient assigned to the medication under study.

Can number needed to treat be negative?

A negative number needed to treat indicates that the treatment has a harmful effect. An NNT=−20 indicates that if 20 patients are treated with the new treatment, one fewer would have a good outcome than if they all received the standard treatment.

What does a small NNT mean?

It is a simple statistical concept called the “Number-Needed-to-Treat”, or for short the 'NNT'. The NNT offers a measurement of the impact of a medicine or therapy by estimating the number of patients that need to be treated in order to have an impact on one person.

What is number to harm?

The number needed to harm (NNH) is a derived statistic that tells us how many patients must receive a particular treatment for 1 additional patient to experience a particular adverse outcome. Lower NNT and higher NNH values are associated with a more favorable treatment profile.

Do you round up or down for number needed to harm?

A more cautious convention is to round the number needed to treat (NNT) up, to avoid overstating the effectiveness, and to round the number needed to harm (NNH) down, to avoid understating the harms (BMJ 2011). BMJ (2011) Helping you to practise evidence-based medicine. Clinical Evidence glossary.

How to calculate NNS?

So as before, the NNS can be calculated by taking 100 and dividing it by the ARR: NNS = 100/ARR = 100/0.5= 200. That means 200 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.

How does NNT help?

How NNT helps. This means that 99 people need to take the drug, pay for it, run the risk of side effects, and stand no chance of benefit. Of course, no one knows going in who will be that lucky 1 out of 100 who does benefit. This is the the power of NNT. It gives a sense of scale to discussions regarding potential harms and benefits.

What is the NNT statistic?

One statistic that can help is called the Number Needed to Treat, or NNT. The NNT tells us the number of people we need to give a drug (or other intervention) to in order for just one person to receive a benefit (or, to prevent just one adverse outcome).

What does NNS mean in medical terms?

Number Needed to Screen (NNS): The number of people who need to be screened (for a given duration) to prevent one death or one adverse event. This is based on the absolute risk reduction (ARR), or how much the risk decreases with a given screening technique.

Can NNT be misinterpreted?

There also has been some work showing that using NNT alone can be misinterpreted by patients.

What is the NNT in epidemiology?

Number needed to treat. Group exposed to a treatment (left) has reduced risk of an adverse outcome (grey) compared to the unexposed group (right). 4 individuals need to be treated to prevent 1 adverse outcome (NNT = 4). The number needed to treat ( NNT) is an epidemiological measure used in communicating the effectiveness ...

What is a type of study that would occur only if both the control and the tested treatment carried significant risks of

This is typically a type of study that would occur only if both the control and the tested treatment carried significant risks of serious harm , or if the treatment was unethical for a healthy participant (for example, chemotherapy drugs or a new method of appendectomy - surgical removal of the appendix).

What is the NNT of a control group?

Every person in the control group shows no improvement, therefore the condition never improves on its own and the control is never effective. NNT is 1/ (1.0-0.0), which is 1. Very effective treatment with large improvement over control. 0.1.

What is NNT in practice?

Explanation of NNT in practice. There are a number of factors that can affect the meaning of the NNT depending on the situation. The treatment may be a drug in the form of a pill or injection, a surgical procedure, or many other possibilities. The following examples demonstrate how NNT is determined and what it means.

What is the meaning of NNT?

The meaning of the NNT is dependent on whether the control group received a placebo treatment or an existing treatment, and, in cases where a placebo treatment is given , the NNT is also affected to the quality of the placebo (i.e. for participants, is the placebo completely indistinguishable from the tested treatment.

Why is NNT important?

The NNT is an important measure in pharmacoeconomics. If a clinical endpoint is devastating enough ( e.g. death, heart attack ), drugs with a high NNT may still be indicated in particular situations. If the endpoint is minor, health insurers may decline to reimburse drugs with a high NNT.

What is NNT in medical terms?

The number needed to treat ( NNT) is an epidemiological measure used in communicating the effectiveness of a health-care intervention, typically a treatment with medication. The NNT is the average number of patients who need to be treated to prevent one additional bad outcome (e.g. the number of patients that need to be treated for one ...

What is the NNT?

The idea of NNT provides clinicians with a method of explaining the relative benefit or harm of a given therapy for a patient. Because of its simplicity, NNT has the following weaknesses: It is usually described as a point estimate instead of a confidence interval of the observed therapeutic effect.

Is NNT linear over time?

The NNT of a given treatment will be very different when describing the value versus placebo instead of another active therapy. The time frame of a given study is important and the benefit of a treatment is usually not linear over time.

Does NNT account for baseline risk?

As with other descriptions of benefit, NNT does not account for a patient's baseline risk. If a patient's individual risk is higher or lower than that studied in a trial, his or her NNT will be lower or higher, respectively. When describing NNT, the comparator is an essential component.

Why is NNT used?

NNT can be used to help us choose between two treatment options. If, for example, the NNT for drug A is lower than that for drug B, it suggests that drug A may be more effective and – all other things being equal – choosing A rather than B would make sense.

What is the NNT in a control group?

The NNT is the reciprocal of the absolute risk reduction – the difference between the proportion (or rate) of events in the active treatment intervention group (Pa), and the proportion (or rate) of events in the control group (Pc):

What is NNT dependent on?

The NNT is dependent on a number of factors including baseline risk and duration of follow-up, so care must be taken when generalising to populations and when comparing NNTs between studies.

What is NNT in medical terms?

First described in 1988 1, the number needed to treat (NNT) can be thought of as the number of patients that need to be treated in order for one to benefit. It provides an attractive means of summarising the results of a clinical trial in a single figure, because the meaning of a sentence such as ‘20 patients need to be treated to avoid one ...

Is the NNT negative in a prophylactic treatment?

It is important to distinguish between treatments and preventative (prophylactic) measures. In trials of prophylactic treatments, ideally fewer events will occur in the treatment arm versus the control group, so (Pa – Pc) and the NNT will be negative. The calculated NNT value, without the sign, can still be presented.

Is NNT time specific?

All NNTs are time-specific, as the effects of treatment may continue beyond the timeframe of a study. For example, in studies looking at the effect of statin therapy in preventing strokes, the NNT from a study running for 1 year will not be directly comparable to that from a study with a 5-year follow-up.

What happens if you don't get treatment for mental health?

There are a number of negative ramifications associated with not getting treatment for a mental health disorder. Certainly, mental health disorders will have specific types of risks or effects that occur as a result of not being addressed. All mental health disorders have the potential for general negative effects occur if left untreated.

What happens if you only experience a few symptoms of mental health?

As a result, the longer one waits to have their mental health disorder treated, the more complicated it becomes and the harder it becomes treat.

How often should you check parasite density?

falciparum infection, patients should be hospitalized to monitor clinical response, and check parasite density every 12–24 hours until clinical presentation improves and a decrease in parasite density becomes apparent.

When should malaria treatment be initiated?

Ideally malaria treatment should not be initiated until the diagnosis has been established by laboratory testing. “Presumptive treatment”, i.e., without prior laboratory confirmation, should be reserved for extreme circumstances, such as strong clinical suspicion of severe disease in a setting where prompt laboratory diagnosis is not available.

What is the best treatment for P. falciparum?

For P. falciparum infections acquired in areas with chloroquine resistance, four treatment options are available. These include artemether-lumefantrine (Coartem™), which is the preferred option if readily available, and atovaquone-proguanil (Malarone™). These are fixed-dose combination therapies that can be used for pediatric patients ≥5 kg. Quinine sulfate plus doxycycline, tetracycline, or clindamycin is also a treatment option. For the quinine sulfate combination options, quinine sulfate plus either doxycycline or tetracycline is generally preferred to quinine sulfate plus clindamycin because there are more data on the efficacy of quinine sulfate plus doxycycline or tetracycline. Quinine should be given for 3 days, except for infections acquired in Southeast Asia where 7 days of treatment is required. The fourth option, mefloquine, is associated with rare but potentially severe neuropsychiatric reactions when used at treatment dose. We recommend this option only when the other options cannot be used. In addition, mefloquine is not recommended for infections acquired in certain parts of Southeast Asia due to drug resistance. Once a treatment regimen is started, if it is being tolerated, there is no need to switch regimens even if a preferred regimen becomes available.

How often should you have a blood smear for malaria?

However, because non-immune individuals may be symptomatic at very low parasite densities which may be initially undetectable, blood smears should be repeated every 12–24 hours for a total of three sets before the diagnosis of malaria can be ruled out.

How to diagnose malaria?

Laboratory diagnosis of malaria can be made through microscopic examination of thick and thin blood smears. Thick blood smears are more sensitive in detecting malaria parasites because the blood is more concentrated allowing for a greater volume of blood to be examined; however, they are more difficult to read.

Is BinaxNOW a diagnostic test?

Several antigen detection tests (rapid diagnostic tests or RDTs) using a “dipstick” or cassette format exist, but only one, BinaxNOW™, is approved for diagnostic use in the United States.

Is malaria a nationally notifiable disease?

Malaria is a nationally notifiable disease. We encourage clinicians to report all cases of laboratory-confirmed malaria to their state health department to help CDC’s surveillance efforts. Refer to the information on the Malaria Case Surveillance Report Form for instructions on how to report a malaria case.

Overview

Modern Approach to NNT

The above calculations for NNT are valid under monotonicity, where treatment can't have a negative effect on any individual. However, in the case where the treatment may benefit some individuals and harm others, the NNT as defined above cannot be estimated from a Randomized Controlled Trial (RCT) alone. The inverse of the absolute risk reduction only provides an upper bound, i.e., .

Relevance

Explanation of NNT in practice

Real-life example

See also

External links