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Press Statement

Preasr√°iteas

12 September 2017

Change in emphasis in reporting average house prices

Median more appropriate than mean

The Central Statistics Office (CSO) today (12th September 2017) publishes the Residential Property Price Index July 2017 with some changes to how average house prices are reported.

These changes have no effect on the index itself.

The CSO is shifting focus to median prices from mean prices in its publications and tools.

Whilst the CSO will continue to publish both median and mean residential property price statistics in its StatBank tables, median prices will be emphasised in the publication format.

Commenting on this, Gregg Patrick, the lead statistician for residential property price statistics, stated: “Median price is a more appropriate measure of central tendency or what the typical buyer pays than mean price, as the latter is often skewed by exceptional high value properties.

In particular, this change in emphasis will affect the House Prices by Eircode tool, which will now report the median price instead of the mean price."

In order to help users understand the difference between mean and median, the CSO has produced a video on this topic.

 

Today's publication is available on the CSO website at Residential Property Price Index July 2017

Technical note

In statistics there are various measures that allow us to represent the characteristics of a group. The characteristics of interest could be, for example, the ages of a group of people, the wages of a group of workers or the price of a group of houses.

One of the most commonly used statistical measures is the mean (the ‘arithmetic mean’ to be precise, but more often simply termed the ‘average’). The mean is the sum of the characteristics of the group (e.g. ages, wages or prices) divided by the number in the group.

However, when we wish to describe the central tendency of the group, the mean is not the most appropriate measure.  For example, if the group contains some elements with exceptionally high characteristic values, these will push the arithmetic mean well above the central tendency of the group.

To represent the central tendency of a group, median is the appropriate statistical measure. The median is found by ordering the group characteristics in ascending value and selecting the middle one.

The median is a better measure of the central tendency of the group as it is not skewed by exceptionally high or low characteristic values.

For further information contact:

Gregg Patrick (+353) 21 453 5202 or Dan Gallagher (+353) 21 453 5210

or email rppi@cso.ie

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