<p>I have two indices with different base years. 
The first is car registrations which is an index with the base year of 2010. 
The other is harmonized index of car prices, with a base year of 2005. </p>

<p>The two are not comparable, so I need to change the base year of one of the variables to 2010. The problem is that the data is quarterly, so I'm not sure exactly how to proceed.</p>

CC BY-SA 3.0
2015-03-13T10:50:12.283Z
Why should the fact that it is quarterly make a difference?
410 gone
CC BY-SA 3.0
2015-03-13T16:56:46.140Z
Well the base year = 100. But the values I have are quarterly, not annual. So I don't know how exactly to change the base.
With annual data values I'd just divide the index with the new base year value and multiply by 100, I'm not sure how to do that with quarterly values.
user3078258
CC BY-SA 3.0
2015-04-28T11:29:22.317Z
So you're are interested by the level, not the growth of your series? Does the simple mean of your 4 points for 2010 and 2005 is exactly 100?
Yann
CC BY-SA 3.0
2015-05-13T00:47:57.493Z
I voted to leave open, since the OP needs help on what to do when the data are quarterly. It is helpful to clarify whether something different has to be done compared to the case of some other frequency, say yearly, or not.
Alecos Papadopoulos
<base-year>
How to change the base year of a quarterly index
user3078258
# How to change the base year of a quarterly index

(Asked by: username_0 on 2015-03-12)

I have two indices with different base years.
The first is car registrations which is an index with the base year of 2010.
The other is harmonized index of car prices, with a base year of 2005.

The two are not comparable, so I need to change the base year of one of the variables to 2010. The problem is that the data is quarterly, so I'm not sure exactly how to proceed.

**Tags:** base-year

> **Comments:**
> **username_1**: Why should the fact that it is quarterly make a difference?  
> **username_0**: Well the base year = 100. But the values I have are quarterly, not annual. So I don't know how exactly to change the base. With annual data values I'd just divide the index with the new base year value and multiply by 100, I'm not sure how to do that with quarterly values.  
> **username_2**: So you're are interested by the level, not the growth of your series? Does the simple mean of your 4 points for 2010 and 2005 is exactly 100?  
> **username_3**: I voted to leave open, since the OP needs help on what to do when the data are quarterly. It is helpful to clarify whether something different has to be done compared to the case of some other frequency, say yearly, or not.  

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## 0 answers

