web analytics

Polity: X more thoughts on poll bias

Written By: - Date published: 11:36 am, February 26th, 2014 - 26 comments
Categories: national, nz first, polls - Tags: , ,

Rob Salmond at Polity has some changing thoughts on the subject of poll bias.

Whenever the media report on polls, they get accused of all manner of biases by the blinkered commentariat. Most of it is nonsense, of course. But some criticism of the polling methods themselves may have more merit that I first thought.

I have been keeping track of the polls in New Zealand for a few years now, mainly trying to get the rightindustry average level of support for each party, and figuring out ways to account for the biases in individual pollsters’ methods. Polity’s Poll of Polls is part of this work, as was the academic work I did uncovering bias in the old version of the Colmar Brunton poll.

But both Danyl at the Dim-Post and Gavin White at UMR have been looking at something more fundamental – is the polling industry biased as a whole? There is certainly a small enough number of competing firms in the market, and enough limitations on their work (e.g. the cost of calling mobiles) for bias to conceivably sneak in. For example, the best information I have seen suggests that the New Zealand population with access to a landline skew about 1.7% more towards National than the population as a whole. Calling a random selection of landlines, even if you do some weighting by demographics, can easily give you a result reflecting this bias.

Is this what is happening in New Zealand? Using quite different methods (but the same raw data), Danyl and Gavin both come to the conclusion that the New Zealand polling industry overstates National, modestly overstates the Greens, understates New Zealand First, and gets Labour about right.

I can see reasons other than poll bias why election results for the Greens may not reflect their polling. It could easily be that the young people who make up a lot of the Greens’ support base are just not very reliable when it comes to turning out in elections.

And the mechanism most people give for poll bias – the non-representative subset of the people who have landlines, should lead pollsters to overestimate New Zealand First with its older support base, not underestimate them. The underestimate of New Zealand First does not seem to fit the causal story people are telling.

But the fairly consistent results on National are harder to dismiss. In each of the last three elections we have been left staring at the chicken bones trying to explain how National’s support seemed to fall away in the dying days. A delayed Brethren effect? Collective panic at the thought of one party government? Maybe. Or maybe these are just the stories we tell ourselves in order to feel comfortable with the polls.

(Having said that, the polls in 2008 and 2011 did actually show a late-term decline for National, just not one big enough to account for the actual result. So the pollsters were not at all surprised in either case that National’s support was lower than its early campaign peak, but they were surprised just how far National had fallen.)

I was caught short in 2011 relying on the polling industry average by falsely projecting that National would get enough votes to govern alone, and that New Zealand First would not break 5%. I was wrong on both counts, and in exactly the direction that Danyl and Gavin would predict. Some might say that is all the evidence you need of bias.

Ultimately, however, I am not sold just yet on the notion of industry-level bias.

The studies Danyl and Gavin have done here can claim as many poll-level observations as they like, but in an important sense the number of elections is the number of observations, because that is the number of times you observe the true value of the things we are busy estimating. Which means right now we are operating on N equals three. Making conclusions on an N this small is risky.

While I’m not yelling “fire” at this stage, I do think there may be smoke. I did not think that three years ago.

If later this year we have to wave our hands at yet another inexplicable final week decline for National, and again marvel at Winston’s ability to sneak up on everyone at the last second, then that will substantially strengthen the claim of industry-wide bias.

If we find there is this bias down the track, then we will have to look very carefully at the way in which a slanted perception of the political reality today impacts on voters’ minds, usually through the journalistic filter. Do they unfairly nurture the reputations of over-estimated parties like National and the Greens, and unfairly tarnish New Zealand First. Does it have real consequences for those parties at the ballot box in an MMP environment? And, of so, is that political speech that should be protected, or protected against?

26 comments on “Polity: X more thoughts on poll bias ”

  1. Blue 1

    Do they unfairly nurture the reputations of over-estimated parties like National and the Greens, and unfairly tarnish New Zealand First.

    The media don’t really care what the poll results are when it comes to how they represent certain parties. Witness two pieces in the Herald today focused on the 0% wonder.

    Their beef with NZ First is mostly journos having personal feuds with Winston Peters.

    If anything, the poll results which overestimate National simply give the media more of an excuse to downplay Labour, which they do anyway.

    • Crunchtime 1.1

      That doesn’t necessarily hold true when you are talking about a party with a large support base. If it looks (falsely) like a foregone conclusion that a party will win a majority vote, or close to, then it’s likely to demoralise and demotivate those who might vote against them.

      I’m not saying this is entirely to blame for the record-breaking 800,000 who didn’t vote last election, but I would suggest it’s one of many contributing factors.

    • Crunchtime 1.2

      …in addition, isn’t there the type of person who tends to vote with who seems to be the “winner” in order to give a “stable government”?

      If so then polls that show National as reasonably far ahead will have a gravitational effect, as it were, on future poll results favouring National, including the ultimate poll results of the election.

      Furthermore isn’t this a big reason why Labour has been polling so poorly for the past half decade, because it has been well publicised as being “divided” and therefore “unstable”? To be fair, Labour haven’t really done enough to dispel that notion.

  2. McFlock 2

    It also seems to me that there seems to be a bit of a bias towards the government of the day. No real data to back it up, though

    • Tracey 2.1

      I agree and think it is probably related tot he amoun to fmedia exposure a PM gets, compared to a LofO. Understandably the PM is a go to on many many things.

      I wonder, what would change, if anything, if published polls were outlawed in an election year?

    • Pasupial 2.2

      McFlock

      Polls do generally favour the incumbent. Most of the research on this is from a US setting, which I can’t be bothered churning through right now. This is the closest that I’ve been able to find to a NZ example thus far:

      http://www.digipoll.com/library/election-polling

      You can see the higher digipoll numbers than votes achieved on election night for the incumbent National in 2011 (51% vs 47%) and Labour in 2005 (45% vs 41%). The transition years contradict this however; in 1999 Labour was favoured in the poll (40% vs 39%), in 2008 National (48% vs 45%). Plus in 2002 National was favoured in the digipoll (23% vs 21%).

      I really need to get more NZ data on this though. The digipoll numbers seem to be averaged across the election year. Online; Roy Morgan only goes back to January 2012, and; Colmar Brunton to February 2011.

    • JK 2.3

      that didn’t happen with Helen Clark in her final term ….. media were very biased against her.

  3. Lanthanide 3

    “And the mechanism most people give for poll bias – the non-representative subset of the people who have landlines, should lead pollsters to overestimate New Zealand First with its older support base, not underestimate them. The underestimate of New Zealand First does not seem to fit the causal story people are telling.”

    Do elderly living in rest homes have their own individual phone lines? I’d suggest not all of them would.

    • Tracey 3.1

      If it is like other types of residential care there is a main line with a voice message allowing you to input the extension you require or else wait to get the reception?

      • Lanthanide 3.1.1

        Right, in which case there would only be 1 number in the phone book which would cover all residents, rather than 1 line per resident.

        So that would help to explain some of why NZ1st is under-represented.

  4. Ant 4

    How many people have their numbers listed these days anyway?

    • Pasupial 4.1

      Ant

      They don’t need a phone listing – they’ve got computers configured to generate random 7 digit numbers (plus area prefix). Or in Colmer Brunton speak; “Nationwide random digit dialling of landline telephones using stratified random probability sampling”.

      • Ant 4.1.1

        Cheers for that, for some reason I had it in my head that calling like that was legislated against and they had to use public information.

      • jaymam 4.1.2

        The random phone numbers are driven by a table for each telephone exchange that shows the telephone numbers actually in use. If those tables have not been updated since the program was supplied (by me!) to the pollster, the newly added numbers and new exchanges will not be polled. Those will tend to be in the outer cheaper suburbs where they are more likely to be lefties.

        • Pasupial 4.1.2.1

          Cheers for that info jaymam. Any idea how often those number tables are updated in the company you’ve had dealings with? [to remained unnamed obviously]

          • jaymam 4.1.2.1.1

            The director that I gave the program to ended up suing the programmer for a lot of money, for a different program. So I doubt that the tables have ever been updated. It is very possible they use a different program now, but they possibly think that nobody would notice if they don’t call all the new numbers.That director has now fallen out with the company that bears her name and now does some polling on her own, which has been widely criticised.

  5. fambo 5

    I wonder how difficult it would be for external agencies to manipulate polls to destabilise a government. They could, for instance, pump large sums of money into setting up their own polling company. Or ferret their operatives into positions of importance in extant polling companies.

  6. rain33 6

    Polls Shmolls, who can forget the embarrassing fail of the right wing, namely Dick Morris and Dean Chambers who had Romney winning the 2012 US election right up until the night of the election? Their methods of ‘unskewing’ the polls sounded quite justified, by re-weighting the sample to match what they believed the electorate would look like in terms of party identification, but as history has proven were completely off the mark.

    I would highly recommend the book The Signal and the Noise: Why Most Predictions Fail – but Some Don’t – by Nate Silver the ‘god of polling’ and American statistician, who in the 2012 US Presidential election correctly predicted the outcome of all 50 States and the District of Columbia, that same year his U.S. Senate race predictions were correct in 31 of 33 States, in 2008 he got 35/35

    Individual polls are an indication of a moment in time. However, when polls start to indicate a trend, that is worth paying attention to. That should be of a concern to Labour. The debate regarding cellphones versus landlines etc was discussed ad-nauseum in the US but became a mute point. For all we know people who have landlines are more likely to turn up and vote at the election booth than people who don’t have landlines. You will get giddy trying to work out all the variables. Instead Labour should be focusing on getting a cohesive message out to the voting public.

  7. Whatever next 7

    Do our polls use the same polling techniques as Nate Silver?

    • Lanthanide 7.1

      Nate Silver didn’t perform any polling himself, he just aggregated and number-crunched the polls that others did.

      In the process he uncovered statistical proof that one of the polling companies was deliberately biasing their polls towards the republicans – they shut up shop after that IIRC.

    • Tamati 7.2

      As said above, Silver doesn’t poll. Silver uses what’s called Bayesian statistics. It’s a totally different way of looking at sampling and prediction and is very trendy ATM.

      Unfortunately it would be very hard to replicate here because we too few polls and under MMP you don’t have an absolute ‘winner’ like you do in FPP,

  8. swordfish 8

    Here are the Poll averages from previous Election years for both (1) February (to help anticipate 2014 Election result from current (February) polling) and (2) the 4-week period immediately before the particular Election (with Election Result comparisons):

    2011

    Nat (Feb average) 53% / Election 47% (minus 6 points)
    Nat (Final 4-weeks average) 52% / Election 47% (minus 5 points)

    Lab (Feb average) 33% / Election 27% (minus 6 points)
    Lab (Final 4-weeks average) 28% / Election 27% (minus 1 point)

    Green (Feb average) 8% / Election 11% (plus 3 points)
    Green (Final 4-weeks average) 12% / Election 11% (minus 1 point)

    NZF (Feb average) 3% / Election 7% (plus 4 points)
    NZF (Final 4-weeks average) 3% / Election 7% (plus 4 points)

    2008

    Nat (Feb average) 53% / Election 45% (minus 8 points)
    Nat (Final 4-weeks average) 47% / Election 45% (minus 2 points)

    Lab (Feb average) 34% / Election 34% (Equal)
    Lab (Final 4-weeks average) 35% / Election 34% (minus 1 point)

    Green (Feb average) 6% / Election 7% (plus 1 point)
    Green (Final 4-week average) 8% / Election 7% (minus 1 point)

    NZF (Feb average) 3% / Election 4% (plus 1 point)
    NZF (Final 4-weeks average) 3% / Election 4% (plus 1 point)

    2005

    Nat (Feb average) 37% / Election 39% (plus 2 points)
    Nat (Final 4-weeks average) 40% / Election 39% (minus 1 point)

    Lab (Feb average) 45% / Election 41% (minus 4 points)
    Lab (Final 4-weeks average) 40% / Election 41% (plus 1 point)

    Green (Feb average) 5% / Election 5% (Equal)
    Green (Final 4-weeks average) 6% / Election 5% (minus 1 point)

    NZF (Feb average) 5% / Election 6% (plus 1 point)
    NZF (Final 4-weeks average) 6% / Election 6% (Equal)

    Need I say more ? (I need not).

  9. Crunchtime 9

    I was trying to find some info about opinion polls prior to the 2002 election but can’t seem to find any on the internet. There’s a lot of info on opinion polls for 2005 but not the previous…

    All I could find was this story about how polls were pointing to an outright majority, but people “withdrew their support” to deny them this. Clearly, National didn’t benefit from this either, nearly slipping below 20% support, which I believe is far lower than Labour’s support has ever fallen.

    I also found some interesting food for thought: the “Electoral (Public Opinion Polls) Amendment Bill” 2002. This is to outlaw any publicity whatsoever 28 days prior to the election. Because OPINION POLLS INFLUENCE RESULTS. Interesting huh… As if banning them for 28 days is going to make any difference!

    Election results 2002:

    Labour 41.3%

    National 20.9%

    NZ First 10.4%

    Act 7.1%

    Green 7%

    United Future 6.7%

    Progressive 1.7%

    Possibly the most even spread of votes in NZ election history?

    It would be interesting to see what opinion polls were doing leading up to this result.

Recent Comments

Recent Posts

  • Equitable response to Omicron vital
    The Green Party supports the Government’s decision to move Aotearoa New Zealand to traffic light level Red at 11.59pm tonight, but says its success will depend on the support that is made available to the most vulnerable. ...
    3 days ago
  • How we’re preparing for Omicron
    As countries around the world experience Omicron outbreaks, we’re taking steps now to ensure we’re as prepared as possible and our communities are protected. ...
    6 days ago
  • What’s Labour achieved so far?
    Quite a bit! This Government was elected to take on the toughest issues facing Aotearoa – and that’s what we’re doing. Since the start of the pandemic, protecting lives and livelihoods has been a priority, but we’ve also made progress on long-term challenges, to deliver a future the next generation ...
    2 weeks ago
  • Tackling the big issues in 2022
    This year, keeping Kiwis safe from COVID will remain a key priority of the Government – but we’re also pushing ahead on some of New Zealand’s biggest long-term challenges. In 2022, we’re working to get more Kiwis into homes, reduce emissions, lift children out of poverty, and ensure people get ...
    2 weeks ago

  • Government’s Family Package continues to deliver for New Zealanders
    The Families Package helped around 330,000 families in its first year - more than half of all families with children in NZ These families received an estimated $55 per week more from Families Package payments in 2018/19 than in 2017/18, on average Families Package increases to the maximum possible Accommodation ...
    BeehiveBy beehive.govt.nz
    2 hours ago
  • New Zealand retains top spot in global anti-corruption rankings
    Justice Minister Kris Faafoi has welcomed news of New Zealand’s ongoing position as top in the world anti-corruption rankings. The 2021 Corruption Perceptions Index released by global anti-corruption organisation, Transparency International, ranks New Zealand first equal with Denmark and Finland, with a score of 88 out of 100. “This is an ...
    BeehiveBy beehive.govt.nz
    15 hours ago
  • Testing improvements see New Zealand well prepared for Omicron
    New Zealand’s PCR testing capacity can be increased by nearly 20,000 tests per day to deal with a surge in cases as part of our wider COVID-19 testing strategy, Associate Minister of Health Dr Ayesha Verrall said. “We have continued to adapt our public health response to safeguard the health ...
    BeehiveBy beehive.govt.nz
    20 hours ago
  • 5,000 portable air cleaners for schools on their way
    As schools are preparing to return, Education Minister Chris Hipkins has announced 5,000 air cleaners have been ordered for New Zealand schools. “As we know, along with vaccination, testing, good hygiene and physical distancing, good ventilation is important in minimising the risk of airborne transmission of the virus that causes ...
    BeehiveBy beehive.govt.nz
    1 day ago
  • New Zealand to move to Red from 11.59pm today
    All of New Zealand will move to the Red setting of the Covid Protection Framework (CPF) at 11:59pm today as Omicron is potentially now transmitting in the community, Prime Minister Jacinda Ardern says. “Nine COVID-19 cases reported yesterday in the Nelson/Marlborough region are now confirmed as Omicron, and a further ...
    BeehiveBy beehive.govt.nz
    3 days ago
  • Mandatory boosters for key workforces progressing well
    More than 5,785 (82%) border workers eligible for a booster vaccination at 6 months have received it so far, COVID-19 Response Minister Chris Hipkins says. “That’s a really strong uptake considering we announced the requirement the week before Christmas, but we need to continue this momentum,” Chris Hipkins said. “We ...
    BeehiveBy beehive.govt.nz
    3 days ago
  • NZ to move to Red
    Nine COVID-19 cases reported yesterday in the Nelson/Marlborough region have now been confirmed as the Omicron variant, and a further case from the same household was confirmed late yesterday. These cases are in a single family that flew to Auckland on 13 January to attend a wedding and other events ...
    BeehiveBy beehive.govt.nz
    3 days ago
  • New Zealand to provide further help for Tonga
    Aotearoa New Zealand is giving an additional $2 million in humanitarian funding for Tonga as the country recovers from a volcanic eruption and tsunami last weekend, Foreign Affairs Minister Nanaia Mahuta and Defence Minister Peeni Henare said today. This brings Aotearoa New Zealand’s contribution to $3 million. “This support will ...
    BeehiveBy beehive.govt.nz
    5 days ago
  • Quarterly benefit numbers show highest number of exits into work
    The Government’s strong focus on supporting more people into work is reflected in benefit figures released today which show a year-on-year fall of around 21,300 people receiving a main benefit in the December 2021 quarter, Minister for Social Development and Employment Carmel Sepuloni said. “Our response to COVID has helped ...
    BeehiveBy beehive.govt.nz
    6 days ago
  • Northland to move to Orange, NZ prepared for Omicron 
    Northland to move to Orange Rest of New Zealand stays at Orange in preparedness for Omicron All of New Zealand to move into Red in the event of Omicron community outbreak – no use of lockdowns Govt planning well advanced – new case management, close contact definition and testing rules ...
    BeehiveBy beehive.govt.nz
    6 days ago
  • RNZAF C-130 Hercules flight departs for Tonga as Navy vessels draw nearer to Tongatapu
    A Royal New Zealand Air Force C-130 Hercules has departed Base Auckland Whenuapai for Tonga carrying aid supplies, as the New Zealand aid effort ramps up, Foreign Affairs Minister Nanaia Mahuta and Defence Minister Peeni Henare said today. “The aircraft is carrying humanitarian aid and disaster relief supplies, including water ...
    BeehiveBy beehive.govt.nz
    6 days ago
  • New Zealand prepared to send support to Tonga
    New Zealand is ready to assist Tonga in its recovery from Saturday night’s undersea eruption and tsunami, Foreign Affairs Minister Nanaia Mahuta and Defence Minister Peeni Henare said today. “Following the successful surveillance and reconnaissance flight of a New Zealand P-3K2 Orion on Monday, imagery and details have been sent ...
    BeehiveBy beehive.govt.nz
    1 week ago
  • Aotearoa New Zealand stands ready to assist people of Tonga
    The thoughts of New Zealanders are with the people of Tonga following yesterday’s undersea volcanic eruption and subsequent tsunami waves, Foreign Affairs Minister Nanaia Mahuta says. “Damage assessments are under way and New Zealand has formally offered to provide assistance to Tonga,” said Nanaia Mahuta. New Zealand has made an ...
    BeehiveBy beehive.govt.nz
    1 week ago
  • Record high of new homes consented continues
    In the year ended November 2021, 48,522 new homes were consented, up 26 per cent from the November 2020 year. In November 2021, 4,688 new dwellings were consented. Auckland’s new homes consented numbers rose 25 per cent in the last year. Annual figures for the last nine months show more ...
    BeehiveBy beehive.govt.nz
    2 weeks ago
  • Report trumpets scope for ice cream exports
    Latest research into our premium ice cream industry suggests exporters could find new buyers in valuable overseas markets as consumers increasingly look for tip top quality in food. Economic Development Minister Stuart Nash has released a new report for the Food and Beverage Information Project. The project is run by ...
    BeehiveBy beehive.govt.nz
    2 weeks ago
  • Honouring the legacy of legendary kaumātua Muriwai Ihakara
    Associate Minister for Arts, Culture, and Heritage Kiri Allan expressed her great sadness and deepest condolences at the passing of esteemed kaumātua, Muriwai Ihakara. “Muriwai’s passing is not only a loss for the wider creative sector but for all of Aotearoa New Zealand. The country has lost a much beloved ...
    BeehiveBy beehive.govt.nz
    2 weeks ago
  • Have your say on proposed changes to make drinking water safer
    Associate Minister for the Environment Kiri Allan is urging all New Zealanders to give feedback on proposed changes aimed at making drinking water safer. “The current regulations are not fit for purpose and don’t offer enough protection, particularly for those whose water comes from smaller supplies,” Kiri Allan said. “This ...
    BeehiveBy beehive.govt.nz
    2 weeks ago
  • Planting the seeds for rewarding careers
    A boost in funding for a number of Jobs for Nature initiatives across Canterbury will provide sustainable employment opportunities for more than 70 people, Conservation Minister Kiri Allan says. “The six projects are diverse, ranging from establishing coastline trapping in Kaikōura, to setting up a native plant nursery, restoration planting ...
    BeehiveBy beehive.govt.nz
    3 weeks ago
  • New Zealand congratulates Tonga's new Prime Minister on appointment
    Minister of Foreign Affairs Nanaia Mahuta today congratulated Hon Hu'akavameiliku Siaosi Sovaleni on being appointed Prime Minister of the Kingdom of Tonga. “Aotearoa New Zealand and Tonga have an enduring bond and the Kingdom is one of our closest neighbours in the Pacific. We look forward to working with Prime ...
    BeehiveBy beehive.govt.nz
    3 weeks ago