More strike action is planned by primary school teachers and principals after they rejected a revised pay offer from Minister of Education Chris Hipkins.

Less than a year into its first term, Prime Minister Jacinda Ardern's Government has had to deal with multiple strikes or threats of strike from public sector workers.

Nurses walked off the job in July, 4000 Ministry of Business, Innovation and Employment (MBIE) and Inland Revenue Department (IRD) staff followed suit later that month, primary school teachers were next up with secondary teachers set to join them while court workers from the Ministry of Justice were the latest to strike.

A key theme for running through all of these strike actions has been the claim that pay rates have failed to keep pace with the cost of living and pay increases for other workers.

GEORGE HEARD/STUFF Teachers have been just one group of public sector workers to strike for better pay and conditions in 2018.

Since 2010, pay increases in the public sector have tended to lag behind the private sector.

That's in contrast to the decade before that, when public sector employees got the better deal.

The upshot is that, in aggregate, public sector pay has increased by 14.6 per cent since 2009, while private sector pay has increased by 17.5 per cent.

Or put another way: public sector pay has grown by 83 cents for every dollar pay has increased in the private sector.

For both private and public sector employees pay increases have been less generous since the global financial crisis of 2008.

The discrepancy holds across most occupational groupings. Professionals in the public sector have seen their pay increase by 14.2 per cent since 2009, compared to 16 per cent for private sector professionals. The difference is similar for managers.

Not all job types have seen bigger increase in private sector, increases for clerical and administrative workers have been about the same.

PUBLIC SECTOR PAY VS COST OF LIVING

Since 2012, annual increases in public sector pay have tended to be above the rate of inflation. The exception was 2011, when inflation increased by 5.3 per cent.

Because of this, the overall increase in inflation since 2009 is greater than the overall increase in public sector pay.

The CPI encompasses changes to the prices of all good and services. We can also look at how prices just for essentials such as food and housing have changed over time.

Changes to public sector pay have consistently lagged behind increases to the cost of housing, which has increased about twice as fast, which is not surprising given the rapid increases to property values and rents over that time.

Food is more variable and has increased about the same rate as public sector pay since 2009.

THE STRIKERS

Of course workers within the public sector are a varied bunch, working in a wide range of jobs for a wide range of organisations.

We can see that overall their pay rates have lagged slightly behind private sector employees since 2009, but how have the groups who went on strike or have threatened to strike fared in that time?

Both nurses and teachers have made a strong case for having been neglected in recent times.

Teachers salaries have not increased at the same pace as the median wage for Kiwi workers.

But even if you were to completely ignore claims that pay rates have lagged, that both professions are struggling to attract and retain staff is a strong market signal that pay rates need to be improved.

Nurses ultimately accepted a nine per cent pay increase and an extension to the number of levels on their pay scale, while teachers are still negotiating.

How about workers at MBIE, IRD and the Ministry of Justice?

Since 2009 the average salary at IRD and the Ministry of Justice has increased by about 20 per cent – 21.6 per cent at IRD and 19.2 per cent at Justice.

A caution with these figures: they are prone to fluctuation caused by changes in staff composition – for example simply by losing a number of lower paid jobs the average salary can increase without the person on the actual average salary earning any more money. Significant pay increases at the top end can have the same effect.

For these reasons it may not be fair to compare them directly to the LCI data above.

We still can see that these organisations have had fairly steady increases to the average salary of about two per cent per year over the past decade.

MBIE was only created in 2012, and since 2013 the average salary at the organisation has increased about seven per cent, or about 1.7 per cent per year.

These are average pay figures, different workers within these organisations will have received different levels of pay increases, which might explain why some – and not all – of them opted to strike.