# Prior predictive check

**URL:** <https://discourse.mc-stan.org/t/prior-predictive-check/24052>\
**Category:** Modeling\
**Tags:** specification\
**Created:** [August 20, 2021, 9:09am UTC](https://discourse.mc-stan.org/t/prior-predictive-check/24052 "2021-08-20T09:09:29Z")\
**Posts on this page:** 1\
**Showing post:** 3

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**Author:** ![mbjoseph](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.mc-stan.org/mbjoseph/32/870_2.png) [@mbjoseph](https://discourse.mc-stan.org/u/mbjoseph)\
**Post date:** [August 25, 2021, 5:54pm UTC](https://discourse.mc-stan.org/t/prior-predictive-check/24052/3 "2021-08-25T17:54:58Z")

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`normal_rng` will return a scalar value when the arguments (mean, sd) are scalars.

Solutions include:

- using a loop to call `normal_rng(0, 2)` for each element
- passing vectors as arguments to `normal_rng`

For more info check out this thread: [Applying Vectorization in generated quantities section](https://discourse.mc-stan.org/t/applying-vectorization-in-generated-quantities-section/13769)

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