What is the evidence that the government's benefit cap is 'having the desired effect' and moving people into work? As the policy was only rolled out this week, we can only ask about how people's anticipation of the cap might have affected decisions, but on the evidence offered by DWP, very few people could plausibly be held to have moved into work in response to the cap. This apparent lack of response would throw the claimed rationale for the cap into question if that rationale had any credibility in the first place. Meanwhile, people should worry less about whether the government is confusing correlation with causality and focus on how weak the causal impact of the cap on employment would be on the most generous assumptions.
Caveat: this post does not attempt to estimate the impact of the cap and the percentages I've calculated are purely illustrative. The conclusion is not that X% of people meet the basic criteria for 'moving into work in reponse to the cap'. It is that the percentage is very small on the weak evidence we have.