A consultant neurologist reviews the findings of a randomised control trial comparing a new anti-epileptic drug to sodium valproate. Amongst patients taking the new drug, the incidence of seizures at 3 months was 8%, compared to 33% for those taking sodium valproate.

Calculate the number needed to treat with this new anti-epileptic drug in order to prevent one seizure.

Options:
explanation: To determine number needed to treat, start by calculating the absolute risk difference. This is the percentage of incidents (incidents being seizures in this case) in the control group (those taking sodium valproate) minus the percentage of incidents in the intervention group (those taking the new drug). For this example that would be 33 - 8 = 25. From here, the number needed to treat is simply 1/ the absolute risk difference. Bear in mind that you need to express the absolute risk difference as a integer between 0 and 1, so 0.25 in this example (1/0.25 = 4).
name: 8
label: d
answer: no
explanation: It looks as though you have added the difference in percentages between the control and intervention group rather than subtract them.

To determine number needed to treat, start by calculating the absolute risk difference. This is the percentage of incidents (incidents being seizures in this case) in the control group (those taking sodium valproate) minus the percentage of incidents in the intervention group (those taking the new drug). For this example that would be 33 - 8 = 25. From here, the number needed to treat is simply 1/ the absolute risk difference. Bear in mind that you need to express the absolute risk difference as a integer between 0 and 1, so 0.25 in this example (1/0.25 = 4).
name: 2
label: c
answer: no
explanation: To determine number needed to treat, start by calculating the absolute risk difference. This is the percentage of incidents (incidents being seizures in this case) in the control group (those taking sodium valproate) minus the percentage of incidents in the intervention group (those taking the new drug). For this example that would be 33 - 8 = 25. From here, the number needed to treat is simply 1/ the absolute risk difference. Bear in mind that you need to express the absolute risk difference as a integer between 0 and 1, so 0.25 in this example (1/0.25 = 4).
name: 32
label: e
answer: no
explanation: To determine number needed to treat, start by calculating the absolute risk difference. This is the percentage of incidents (incidents being seizures in this case) in the control group (those taking sodium valproate) minus the percentage of incidents in the intervention group (those taking the new drug). For this example that would be 33 - 8 = 25. From here, the number needed to treat is simply 1/ the absolute risk difference. Bear in mind that you need to express the absolute risk difference as a integer between 0 and 1, so 0.25 in this example (1/0.25 = 4).
name: 4
label: a
answer: yes
explanation: It looks as though you have added the difference in percentages between the control and intervention group rather than subtracting them.

To determine number needed to treat, start by calculating the absolute risk difference. This is the percentage of incidents (incidents being seizures in this case) in the control group (those taking sodium valproate) minus the percentage of incidents in the intervention group (those taking the new drug). For this example that would be 33 - 8 = 25. From here, the number needed to treat is simply 1/ the absolute risk difference. Bear in mind that you need to express the absolute risk difference as a integer between 0 and 1, so 0.25 in this example (1/0.25 = 4).

The number needed to treat must always be rounded to a whole number!
name: 2.43
label: b
answer: no

Correct answer: a