# how to calculate mean follow up

#### statfran23

##### New Member
If i have 5 patients, 1 is followed for 40 months, 1 for 38, 1 for 37, 2 for 30 motnhs, which is the mean follow up. someone can explain me how to calculate ? which is the correct formula ? thank you

#### ondansetron

##### TS Contributor
What is the formula for arithmetic average?

#### ondansetron

##### TS Contributor
I'm not saying it's wrong, but I'm asking why are you using that formula?

Why not (.2)*(40 + 38 +37) + (.4)*(30) ?

(Trying to encourage some learning, metacognition.)

If that is the right formula, do you think the median would be more appropriate here? What about the mode?

#### statfran23

##### New Member
I'm not saying it's wrong, but I'm asking why are you using that formula?

Why not (.2)*(40 + 38 +37) + (.4)*(30) ?

(Trying to encourage some learning, metacognition.)

If that is the right formula, do you think the median would be more appropriate here? What about the mode?
sorry but i don't understand your formula ? If i am doing a clinical study and i am following the patients, i just want to know which is the mean follow up.

#### ondansetron

##### TS Contributor
I'll try to grease the wheels:
1) the formula I gave is just another way of writing your formula.
2) Where are you getting the formula that you're suggesting?

The point is to encourage some independent search and discovery. Did the formula come from a website, a book? Trying to use the teach a man to fish principle.

So yes, the arithmetic average/mean is the sum of the values divided by the number of values. In general for follow-up, it might be a better idea to look at median follow up rather than mean since it's not uncommon to have huge outliers in followup, or for shorter periods, the distribution is naturally right against the theoretical lower bound of 0 follow up. If there are few values and you're interested in the most common follow up length then mode might be more appropriate. Usage of statistics in medicine requires more thought than is currently encouraged (from an insider perspective), so I'm trying to encourage a bit more prodding and inquiry in to being able to answer "Is this the right formula or approach?"

#### statfran23

##### New Member
I'll try to grease the wheels:
1) the formula I gave is just another way of writing your formula.
2) Where are you getting the formula that you're suggesting?

The point is to encourage some independent search and discovery. Did the formula come from a website, a book? Trying to use the teach a man to fish principle.

So yes, the arithmetic average/mean is the sum of the values divided by the number of values. In general for follow-up, it might be a better idea to look at median follow up rather than mean since it's not uncommon to have huge outliers in followup, or for shorter periods, the distribution is naturally right against the theoretical lower bound of 0 follow up. If there are few values and you're interested in the most common follow up length then mode might be more appropriate. Usage of statistics in medicine requires more thought than is currently encouraged (from an insider perspective), so I'm trying to encourage a bit more prodding and inquiry in to being able to answer "Is this the right formula or approach?"
thank you for reply me, right now it's everything more clear