Looking at the docs, we have:

“”"

We also need to make sure that every pyro.sample() statement from the model has a matching pyro.sample() statement in the guide. In our case, we include z in both the model and the guide.

“”"

However, in the example we have:

```
def model(data):
prior_loc = torch.tensor([0.])
prior_scale = torch.tensor([5.])
z = pyro.sample('z', dist.Normal(prior_loc, prior_scale))
scale = torch.tensor([0.1])
with pyro.plate('data', len(data)):
pyro.sample('x', dist.Normal(z*z, scale), obs=data)
```

However, in the guide we have:

```
def guide(data, index):
scale_q = pyro.param('scale_{}'.format(index), torch.tensor([1.0]), constraints.positive)
loc_q = pyro.param('loc_{}'.format(index), torch.tensor([0.0]))
pyro.sample("z", dist.Normal(loc_q, scale_q))
```

What about the `x`

variable?