Dow Jones nearing an all-time high. So what?

The Dow is a silly index for silly people. Pay no heed.

Today could be the day the Dow Jones Industrial Average hits its highest ever mark. And it won't mean a thing.

The DJIA—commonly referred to as just the "Dow"—is one of the most important stock market indexes in America. With the S&P 500 and Nasdaq, it's a useful proxy for the health of American business. When the Dow's up, times are good; when it's down, hold on to your hats.

Later today, it's expected that the Dow will break 14,164.53, the all-time high reached on Oct 9, 2007. It closed at 14,127.82 yesterday, and a slew of "good" reports from Europe—where French, German and UK PMIs came in higher than expected, albeit still signalling contraction for the former—as well as futures contracts due to vest today indicate that nows the time it will break that barrier.

But even if it does, it's a meaningless milestone. Due to the way the Dow is put together, the two marks aren't comparable. So while you will read stories about how "the American market has recovered", they may or may not be true—and this says nothing either way.

Adam Nash describes the problem:

Just thirty stocks, hand picked by committee by Dow Jones, with no rigorous requirements. Worse, it’s a “price-weighted” index, which is mathematically nonsensical. When calculating the Dow Jones Industrial Average, they take the actual stock prices of each stock, add them together, and divide them by a “Dow Divisor“. They don’t take into account how many shares outstanding; they don’t assess the market capitalization of each company. When a stock splits, they actually change the divisor for the whole index. It’s completely unclear what this index is designed to measure, other than financial illiteracy.

In fact, there is only one justification for the Dow Jones Industrial Average being calculated this way. Dow Jones explains it in this post on why Apple & Google are not included in the index. To save you some time, I’ll summarize: they have always done it this way, and if they change it, then they won’t be able to compare today’s nonsensical index to the nonsensical index from the last 100+ years.

The end result is that, as Nash points out, the Dow is only "off its highs" of 2007 because of it made one arbitrary decision rather than another. If Apple had been introduced to the index in 2009 rather than Cisco, the Dow would have broken its high well over a year ago. It would have been nonsensical to report that then; and it's still nonsensical to care now.

Photograph: Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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I believe only Yvette Cooper has the breadth of support to beat Jeremy Corbyn

All the recent polling suggests Andy Burnham is losing more votes than anyone else to Jeremy Corbyn, says Diana Johnson MP.

Tom Blenkinsop MP on the New Statesman website today says he is giving his second preference to Andy Burnham as he thinks that Andy has the best chance of beating Jeremy.

This is on the basis that if Yvette goes out first all her second preferences will swing behind Andy, whereas if Andy goes out first then his second preferences, due to the broad alliance he has created behind his campaign, will all or largely switch to the other male candidate, Jeremy.

Let's take a deep breath and try and think through what will be the effect of preferential voting in the Labour leadership.

First of all, it is very difficult to know how second preferences will switch. From my telephone canvassing there is some rather interesting voting going on, but I don't accept that Tom’s analysis is correct. I have certainly picked up growing support for Yvette in recent weeks.

In fact you can argue the reverse of Tom’s analysis is true – Andy has moved further away from the centre and, as a result, his pitch to those like Tom who are supporting Liz first is now narrower. As a result, Yvette is more likely to pick up those second preferences.

Stats from the Yvette For Labour team show Yvette picking up the majority of second preferences from all candidates – from the Progress wing supporting Liz to the softer left fans of Jeremy – and Andy's supporters too. Their figures show many undecideds opting for Yvette as their first preference, as well as others choosing to switch their first preference to Yvette from one of the other candidates. It's for this reason I still believe only Yvette has the breadth of support to beat Jeremy and then to go on to win in 2020.

It's interesting that Andy has not been willing to make it clear that second preferences should go to Yvette or Liz. Yvette has been very clear that she would encourage second preferences to be for Andy or Liz.

Having watched Andy on Sky's Murnaghan show this morning, he categorically states that Labour will not get beyond first base with the electorate at a general election if we are not economically credible and that fundamentally Jeremy's economic plans do not add up. So, I am unsure why Andy is so unwilling to be clear on second preferences.

All the recent polling suggests Andy is losing more votes than anyone else to Jeremy. He trails fourth in London – where a huge proportion of our electorate is based.

So I would urge Tom to reflect more widely on who is best placed to provide the strongest opposition to the Tories, appeal to the widest group of voters and reach out to the communities we need to win back. I believe that this has to be Yvette.

The Newsnight focus group a few days ago showed that Yvette is best placed to win back those former Labour voters we will need in 2020.

Labour will pay a massive price if we ignore this.

Diana Johnson is the Labour MP for Hull North.