Message-ID: <6b205b97feb14cb0b2e985af48b076aa@UM-MAIL3213.unimaas.nl>
Date: 2020-12-17T09:35:51Z
From: Wolfgang Viechtbauer
Subject: [R-meta] converting escalc ROM outputs to the log-2 scale
In-Reply-To: <CAHP6aVHa_hv2X2J9DkQjf5uNBnRrc8HwWC4ZuaZFxE2NefBDyw@mail.gmail.com>
Dear Divya,
That's just how variances change under multiplicative transformations. The same works with raw data:
x <- rnorm(10)
var(x)
var(2*x)
2^2 * var(x)
Best,
Wolfgang
>-----Original Message-----
>From: Divya Ravichandar [mailto:divya at secondgenome.com]
>Sent: Saturday, 12 December, 2020 1:10
>To: Viechtbauer, Wolfgang (SP)
>Cc: r-sig-meta-analysis at r-project.org
>Subject: Re: [R-meta] converting escalc ROM outputs to the log-2 scale
>
>Hi Dr. Wolfgang
>
>Thank you for getting back to me. Could you help me understand more on why
>we square the log(2) in the vi calculation?
>
>On Fri, Dec 11, 2020 at 6:37 PM Viechtbauer, Wolfgang (SP)
><wolfgang.viechtbauer at maastrichtuniversity.nl> wrote:
>Dear Divya,
>
>If y_i ~ N(theta_i, v_i), then for any constant c, c*y_i ~ N(c*theta_i, c^2
>* v_i).
>
>So, it would be yi_new = yi/log(2) and vi_new = vi/log(2)^2.
>
>Best,
>Wolfgang
>
>>-----Original Message-----
>>From: R-sig-meta-analysis [mailto:r-sig-meta-analysis-bounces at r-
>project.org]
>>On Behalf Of Divya Ravichandar
>>Sent: Friday, 11 December, 2020 23:36
>>To: r-sig-meta-analysis at r-project.org
>>Subject: [R-meta] converting escalc ROM outputs to the log-2 scale
>>
>>Hi all
>>
>>I have a question around changing the scale of *yi *and *vi *exported
>>from *escalc()
>>*function when using *measure=ROM.* Based on the documentation, this
>>function exports *yi *in natural log (ln) scale. --> yi =
>>ln(grp1-mean/grp2-mean) and then the associated vi.
>>
>>I am interested in obtaining the *log-2 fold change. *Is there a way to
>>convert yi & vi from *escalc(measure = ROM,...) *to this scale. Would it be
>>reasonable to simply transform the values by converting from log-e -> log-2
>>scale by
>>yi_new = yi/log(2) and vi_new = vi/log(2)
>>
>>Thank you
>>
>>--
>>*Divya Ravichandar*
>>Scientist
>>Second Genome