9 The pre-release material contains information concerning the median income of taxpayers in different areas of London. Some of the data for Camden is shown in the table below. The years quoted in this question refer to the end of the financial years used in the pre-release material. For example, the year 2004 in the table refers to the year 2003/04 in the pre-release material.
| Year | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 |
| Median | | Income in \(\pounds\) |
| 21300 | 23200 | 24200 | 25900 | 26900 | \#N/A | 28400 | 29400 |
- Explain whether these data are a sample or a population of Camden taxpayers.
A time series for the data is shown below.
\begin{figure}[h]
\captionsetup{labelformat=empty}
\caption{Median income of taxpayers in Camden 2004-2011}
\includegraphics[alt={},max width=\textwidth]{11788aaf-98fb-4a78-8a40-a40743b1fe15-07_624_1469_950_242}
\end{figure}
The LINEST function on a spreadsheet is used to formulate the following model for the data:
\(I = 1115 Y - 2212950\), where \(I =\) median income of taxpayers in \(\pounds\) and \(Y =\) year. - Use this model to find an estimate of the median income of taxpayers in Camden in 2009.
- Give two reasons why this estimate is likely to be close to the true value.
The median income of taxpayers in Croydon in 2009 is also not available.
- Use your knowledge of the pre-release material to explain whether the model used in part (b) would give a reasonable estimate of the missing value for Croydon.