Number Needed to Treat versus Number Needed to Harm?

[Faith-USMLE]

Ive looked for the equations for those.. And found then to be the same!!
=1/absolute risk reduction

So whats the difference?!?

[younissmed]

nnt=1/absolute risk reduction
nnh=1\attributable risk

[Faith-USMLE]

Originally Posted by younissmed

nnt=1/absolute risk reduction
nnh=1\attributable risk

Isnt attributable risk the same as absolute risk reduction?

[med_ziva]

number needed to treat : number of people you need to give experimental treatment to prevent 1% from getting the disease of interest.
Attributable Risk= difference of treated and untreated groups(to medicine)
NNT= 1/AR

number needed to harm : number of people you need to expose to risk factor in order to cause 1% to acquire the disease of interest.
AR= difference of exposed and unexposed (to risk factors)
NNH= 1/AR

[neha_subh]

Originally Posted by med_ziva

number needed to treat : number of people you need to give experimental treatment to prevent 1% from getting the disease of interest.
Attributable Risk= difference of treated and untreated groups(to medicine)
NNT= 1/AR

number needed to harm : number of people you need to expose to risk factor in order to cause 1% to acquire the disease of interest.
AR= difference of exposed and unexposed (to risk factors)
NNH= 1/AR

realy thanks.

now time to solve the question acording to definition.

Q:
Eficacy of new lipid lowering drug marketed (fibrates),clinical control trial at 5yrs given below:

-------------------Treat:with fibrates----------treat:with placebo

MI--------------------20-------------------------------35
non MI---------------980-----------------------------965

number needed to treat????

[med_ziva]

Originally Posted by neha_subh

realy thanks.

now time to solve the question acording to definition.

Q:
Eficacy of new lipid lowering drug marketed (fibrates),clinical control trial at 5yrs given below:

-------------------Treat:with fibrates----------treat:with placebo

MI--------------------20-------------------------------35
non MI---------------980-----------------------------965

number needed to treat????

First to make a table:

Drugs MI
+ -
Fibrates 20 980
placebo 35 965


Absolute Risk Reduction = Event rate in group taking placebo- Event rate in
group taking fibrates ( i.e. number of people in
study to be treated by the drug to prevent MI)

= 35/35+965 - 20/20+980
= 35/1000 - 20/1000
= 1/200
NNT= 1/ ARR = 200

[neha_subh]

Originally Posted by med_ziva

First to make a table:

Drugs MI
+ -
Fibrates 20 980
placebo 35 965


Absolute Risk Reduction = Event rate in group taking placebo- Event rate in
group taking fibrates ( i.e. number of people in
study to be treated by the drug to prevent MI)

= 35/35+965 - 20/20+980
= 20/1000 - 35/1000
= 1/200
NNT= 1/ ARR = 200

i have one question here is that event rate with placebo-event rate group taking drug? how we can put that equation in this scenerio

[med_ziva]

Originally Posted by neha_subh

i have one question here is that event rate with placebo-event rate group taking drug? how we can put that equation in this scenerio

here it simply means that : the event rate in placebo group is the number of the total people in placebo group who had MI by taking the placebo ,out of total number of people receiving placebo.
similarly, event rate in fibrates group is the no. of total people who took the fibrates but still had MI .
So if we substract these two, we can get the total number of people who are at risk of getting MI if they dont take the fibrates drug (or take placebo in this case).
This gives us the absolute risk reduction. And hence number of people we need to treat in order to prevent MI will be 1/ ARR

[neha_subh]

Originally Posted by med_ziva

First to make a table:

Drugs MI
+ -
Fibrates 20 980
placebo 35 965


Absolute Risk Reduction = Event rate in group taking placebo- Event rate in
group taking fibrates ( i.e. number of people in
study to be treated by the drug to prevent MI)

= 35/35+965 - 20/20+980
= 35/1000 - 20/1000
= 1/200
NNT= 1/ ARR = 200

event rate with placebo -- event rate with treatment:

35/1000 -- 20/1000

0.035 -- 0.02 = 0.015
now
1 / ARR
1/ 0.015 = 66.66%

Am i right ???

[neha_subh]

for number needed to harm:

First to make a table:

---------------------- MI-----------------no MI------------

exposure---------- 35------------------965
no exposure--------20 ----------------- 985

now

1/ AR = 35/1000 -- 20 / 1000


1 / AR = 0.035 -- 0.02
1/AR = 1/ 0.015 = 66.66%

Am i right?

[neha_subh]

MED_ZIVA its uw concept:

event rate with placebo -- event rate with treatment:

35/1000 -- 20/1000

0.035 -- 0.02 = 0.015
now
1 / ARR
1/ 0.015 = 66.66%