3.4 Strengths and limitations
Empirical evidence shows that a significant proportion of a country's wealth is held by a minority of the population. This means it is easy to under sample these people. The more uneven the distribution of wealth the more likely it is that the very wealthy will be excluded from the sample (Headey and Wooden, 2004). Furthermore, the wealthier members of the population may have greater incentives to withhold information about the size of their assets. Because of this, the very wealthy are unlikely to be well represented by this study.
There is a one-year difference between the collection of the wealth data, in Wave 2, and the health data, in Wave 3. As the age of diagnosis was asked for the chronic conditions these could be backdated to Wave 2. Self-rated health is asked in every wave, but there is no way to backdate the health measures calculated from the SF36 and K10 health surveys.
It is therefore necessary to assume that reported health from the SF36 and K10 surveys does not differ significantly from one year to the next in order to use them as proxies for health in Wave 2. For many respondents, their actual health in Wave 2 is expected to closely match their recorded health in Wave 3. The health module includes a question as to whether the respondent experienced an illness or injury that hindered their normal activities for seven days or more in the 12 months preceding the interview. For respondents who answered “yes” to this question this assumption is potentially less valid.
The SoFIE survey will collect a vast amount of information over the eight-year period, for which it runs, between 2002 and 2010. Additional waves will enable a more systematic study of the changes in wealth and health over time. Despite the fact that the complete longitudinal data set will only cover eight years, this research will be potentially more powerful than the cross-sectional analysis of the present study. Models of savings over time and comparisons between cross-sections will provide further understanding of how health and wealth change over time.
