CPI now includes e-books and iPads

In a sign of the changing times, tablet computers, e-books and digital movie downloads have been added to the consumer price index, while dictionaries and envelopes drop out.

Statistics New Zealand revises the index every three years, adding and removing items and adjusting their weights in the index.

The revisions reflect changes in what households spend their money on - less butter and more margarine, for example - and changes in relative prices.

After the latest revisions, released yesterday, food now makes up 18.8 per cent of the CPI, up from 17.8 per cent in 2008.

Four food items have been added: dried apricots, frozen berries, frozen chicken nuggets and flatbread.

Alcoholic beverages and tobacco have increased their weighting slightly, from 6.8 to 6.9 per cent.

We are consuming less tobacco but that was more than offset by a hefty increase in tax on the product, which boosted prices.

We are spending more on alcohol too, despite a shift in beer consumption away from licensed premises.

We are eating out in restaurants less.

Takeaways, on the other hand, are up.

The most important data source Statistics NZ draws on to revise the CPI is the household economic survey, which questions 3100 households on what they spend money on and gets them to keep a diary of their spending for two weeks.

The most recent survey was conducted over the year immediately following the 2008/09 recession, which may explain falls in spending on, or related to, big-ticket items.

Construction costs and costs associated with buying and selling houses now make up less of the index than they did, as do furniture and furnishings and household appliances.

The weights given to new and used cars have also fallen.

By contrast, rents have increased their share of the index, from 7.9 to 8.8 per cent, which Statistics NZ says reflects a higher proportion of households renting.

Electricity is a bigger part of the cost of living than three years ago, rising to 3.9 from 3.5 per cent.

Insurance takes a larger share, too, and alarm monitoring services have been added to the CPI.

Reflecting the growing proportion of people's lives spent communing with screens, tablet computers join laptops in the CPI.

External hard drives join memory cards and recordable DVDs, Blu-ray discs join recorded DVDs, e-books join the printed variety, and delivery charges have been added to reflect the increasing prevalence of online purchases.

Overall, the number of items in the CPI basket has risen to 710 from 694.