A fortnight ago, Bill Shorten found himself in the unusual position of making headlines on his own initiative.

In announcing a policy to tighten superannuation concessions for retirees on high incomes, the opposition broke with a small-target strategy that had long seemed to be serving it well in the polls, in a bid to prove that it was serious enough about the budgetary position to self-inflict some pain in addressing it.

It’s not every day that an opposition can be found playing a policy gambit that entails a significant number of losers, and doing it at a time that gives potential opponents well over a year to marshal their forces before the election.

As is all too often the case, the explanation can probably be found in opinion polls — and in particular, in Bill Shorten’s sharply deteriorating personal ratings over the past two months.

The chart below displays trend results of personal approval and preferred Prime Minister ratings from 69 polls conducted by six different pollsters since the 2013 election.

The display on the left shows that Shorten spent most of last year with a highly stable net neutral rating on personal approval, meaning his satisfaction and dissatisfaction ratings were consistently about the same.

This put Shorten exactly in the middle of the field so far as the historical performance of opposition leaders goes, since the average result of all such polling conducted by Newspoll since 1985 is 40% satisfied and 40% dissatisfied.

Depending on the circumstances, a “neutral” rating can mean very different things — at one extreme, that a leader is highly polarising; at the other, that they don’t rouse much of a reaction either way.

There can be little doubt which of the two is nearer the mark in the case of Shorten, whose low-key performance seemed to be getting a bare pass mark from respondents who weren’t expecting him to see the inside of the Lodge any time soon.

Tellingly, the two occasions where Shorten’s rating perked up a little over the past year seemed to have more to do with Tony Abbott’s performance than his own. The first was a slight bump in his favour in May, which looked very much like a short-term secondary effect of the slump in Tony Abbott’s stocks after the budget.

The same effect seemed to be in evidence after the Prince Philip knighthood on Australia Day, which marked the next occasion that Shorten received a net positive rating from Newspoll.

This was followed just days later by the Liberal Party spill motion of February 9 — after which the polling picture changed on multiple fronts, in ways that hadn’t generally been anticipated.

The hostile reaction to the Prince Philip knighthood proved to be a flash in the pan, despite expectations that the instability surrounding the spill vote would help sustain it.

It was followed by a solid Coalition recovery, albeit one that appears to be tapering off, leaving Coalition voting intention and Tony Abbott’s personal approval back where they were late last year.

However, the most striking change since early February has been the strong downward trend in Bill Shorten’s personal ratings from an already lukewarm starting point.

Once again, this appears to have had little to do with Shorten’s own performance, which has been true to his plodding form. Instead, Abbott’s brush with political death looks to have prompted respondents to hold Shorten to a higher standard than before, reflecting a realisation that he may actually end up becoming Prime Minister at some time in the foreseeable future.

Shorten’s downturn will be causing Labor strategists to look with growing concern on the negative bullet points coming out of their focus group research — that he doesn’t stand for anything, and he hasn’t done enough to dispel the damaging notion that Labor lacks the discipline to tackle what more than two-thirds of voters recognise as a problem with the budget.

Certainly it’s still early days, but the first indications as to the success of the superannuation policy in dispelling such notions have been mixed, to say the very least.

A ReachTEL poll conducted for the Seven Network immediately in the wake of the announcement found a positive response in principle, with 57% saying they would “support increasing the tax rate on superannuation contributions for high-income earners”, and only 22.1% opposed.

As yet though, his personal ratings show no sign of pulling out of their downward slide, with this week’s Newspoll result bringing Shorten down to effective parity with Tony Abbott on both net approval (meaning their approval ratings minus disapproval) and preferred prime minister.

Worse still, perhaps, a Morgan phone poll (from an admittedly small sample of 583) recently found Shorten had lost his status as preferred Labor leader — a distinction now belonging to Deputy Leader of the Opposition Tanya Plibersek, who has enjoyed a steady climb from 16% to 23% since last June, while Shorten has remained stranded around his present rating of 21%.