+ Reply to Thread
Results 1 to 5 of 5

Thread: Percentages as a continuous variable

  1. #1
    Points: 8,343, Level: 61
    Level completed: 65%, Points required for next Level: 107

    Posts
    278
    Thanks
    14
    Thanked 7 Times in 7 Posts

    Percentages as a continuous variable




    Hello all

    I have a variable, on a continuous scale, it is some medical value before getting a treatment. After the treatment, this value is being reduced. For some people by 10%, for some by 13%, 15%, 20%, etc,....

    I have two of these treatments, and I am comparing them. Is it legal (I can't think of a reason why not) to compare the mean reduction ? By mean reduction my intention is: if in one group there are 3 patients (just for the example), and the first had reduction of 10%, the second 13% and the third 17%, than I can say that the average reduction was 13.33%. Now I want to compare the mean reduction for both groups. I make a mean of percentages, is it legal ?

    thanks

  2. #2
    Omega Contributor
    Points: 38,432, Level: 100
    Level completed: 0%, Points required for next Level: 0
    hlsmith's Avatar
    Location
    Not Ames, IA
    Posts
    7,006
    Thanks
    398
    Thanked 1,186 Times in 1,147 Posts

    Re: Percentages as a continuous variable

    Instead of percentages, can't you just use the mean differences. What do you get by converting them?
    Stop cowardice, ban guns!

  3. #3
    Points: 8,343, Level: 61
    Level completed: 65%, Points required for next Level: 107

    Posts
    278
    Thanks
    14
    Thanked 7 Times in 7 Posts

    Re: Percentages as a continuous variable

    I can't use the mean difference because the baseline is not the same, not every patient start with the same value
    for example:

    patient 1 started with 30 and reduced to 18
    patient 2 started with 33 and reduced only to 20

    I can't ignore that patient 2 started with a higher score

  4. #4
    TS Contributor
    Points: 22,410, Level: 93
    Level completed: 6%, Points required for next Level: 940

    Posts
    3,020
    Thanks
    12
    Thanked 565 Times in 537 Posts

    Re: Percentages as a continuous variable

    It seems that you assume the the medical value before and after treatment is taking the form M and M(1 - P) respectively; and similar for the other group. And you are doing a hypothesis test, comparing the expected value/mean of the random variable P of the two groups.

    It is nothing illegal; you should concern whether such model assumption is justifiable (like you stated the baseline issue), especially if that is not a common practice in your field. And whether such assumption fulfill your ultimate objective.

  5. #5
    Points: 8,343, Level: 61
    Level completed: 65%, Points required for next Level: 107

    Posts
    278
    Thanks
    14
    Thanked 7 Times in 7 Posts

    Re: Percentages as a continuous variable


    BGM, you are right, this is what I am trying to do. I have reasons for doing it, for example, if I would say that a 15% reduction is a success (legitimate claim in this case) then I would compare the proportion of patients with a success in each group. Since in the control group the success rate is relatively high (the new treatment is assumed to be non-inferior but safer and easier), the sample size I will need will be extremely high, with no practical value (company can't afford it).
    By doing what I asked, I move to a continuous scale, I still have a value to my hypothesis, and the sample size is perhaps not small, but practical. For a company there is a big difference between a sample of 200 patients and 700 patients...

+ Reply to Thread

           




Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats