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There are many ways to illustrate aspects of the distribution of energy expenditure, consumption, income or wealth. In this product, the main indicators used are the mean and quintiles.
Mean household (or average household) values for items such as energy expenditure, energy consumption, gross household income and net wealth, are simple indicators that can be used to show differences between subgroups of the population. The method for calculating means is described in the 'Calculation of population counts, means and medians' section of the Household Energy Consumption Survey, User Guide, Australia, 2012 (cat. no. 4671.0).
Equivalised disposable household income means are person weighted. That is, they are calculated with respect to the relevant number of persons. This enables people in large households to have the same contribution to the mean as people living alone, and is possible because equivalised disposable household income is an indicator of the economic resources available to each individual in a household. The method for calculating person weighted means is also described in the 'Calculation of population counts, means and medians' section of this user guide.
Median values, which are the midpoint when all units are ranked in ascending order values, are another way to indicate differences between subgroups of the population. More information on median values and their calculation can be obtained in the Survey of Income and Housing, User Guide, Australia, 2011-12 (cat. no. 6553.0) chapters featuring measures of income distribution.
When persons (or any other units) are ranked from the lowest to the highest on the basis of some characteristic such as their household income, they can then be divided into equally sized groups. The generic term for such groups is quantiles.
Quintiles, deciles and percentiles
When the population is divided into five equally sized groups, the quantiles are called quintiles. If there are 10 groups, they are deciles, and division into 100 groups gives percentiles. Thus the first quintile will comprise the first two deciles and the first 20 percentiles.
Equivalised disposable household income quintile data are sometimes supplemented by data relating to the second and third deciles combined. The latter is included to enable quintile-style analysis to be carried out without undue impact from very low incomes which may not accurately reflect levels of economic wellbeing (see paragraphs 39 to 41 of the Explanatory Notes).
In some analyses, the statistic of interest is the boundary between quantiles. This is usually expressed in terms of the upper value of a particular percentile. For example, the upper value of the first quintile is also the upper value of the twentieth percentile and is described as P20. The upper value of the third quintile is P50. The median of a whole population is P50, the median of the third quintile is also P50, the median of the first quintile is P10, etc.
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