Randimization without replacement in blocks

[Noga]

Hi David,
Thanks for replying so quickly. Yes, this is exactly what I meant, and
the experiment is indeed programmed as you offer. However, some
pictures appear twice (even though the pictures list is set to Random
and the "Reset on every run" is off). It seems that on each block the
pictures list stays the same (and pictures from previous blocks are
not excluded)

Any Ideas?

Noga

On 30 ינואר, 16:01, "David K McFarlane" <mcfar... at msu.edu> wrote:
> Noga,
>
> Just to make sure I understand, I'll put some example numbers on this.  You
> have, say, 30 pictures, and you want to present 10 pictures each in 3
> blocks, and you want each picture to appear only once across the entire
> session.  If that is the case, then this is probably a job for nested lists.
> Put all 30 pictures in a nested list that will be used by all three blocks.
> Set the nested list to Random selection, and make sure that "Reset on every
> run" is *off*.  Now the 30 pictures will be randomized once, and each block
> will take samples from that one random order.
>
> On the other hand, if you did want to allow pictures to appear only once
> within a block but allow them to reappear across blocks, then turn on "Reset
> on every run" for the nested list.
>
>  -- David McFarlane
>
>
>
>
>
> > My experiment contains 3 blocks with break between them. on each block
> > I present pictures from a list. I want each picture to appear only
> > once! and in random order. My problem is that pictures can appear more
> > than once (the same picture can appear in block 1 and in block 2 or
> > 3). Pictures that appeared in block 1 are not excluded from appearing
> > again in the next blocks.
> > How can I fix it in an elegant way? without separating the pictures
> > list to 3 lists (list for each block)?
>
> > Thanks!
>
> > Noga
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