Fwd: randomization and weight

[Nathaly Stern]

Hello,

Each trial on our experiment include 2 image stimuli that presented one after the other. the first stimuli is a list of 3 words, one of the words is emotional and the other two are neutral. the emotional word appears on a different location on each list stimuli (up/center/down). overall there 60 words lists, on third of the lists(20) the emotional word's location is up, on the other third, it's location is center and on the last third, it's location is down. The order of the lists is randomized. 

Afterwards, the second image stimuli is presented. The second stimuli is a repetition of one of the words presented earlier (critical word). the critical word is presented on a different location on each trial (up/center/down).

We would like for the loaction of the crirical word to be random. In addition, the emotional word should be the critical word on two thirds (2/3) of the trials, even though it's location on the list changes on each trial. Is it possible to randomize the location of the critical word, while maintaining this ratio across the trials?

thank you for your help,

Adi and Nathaly.