Analysis of the raw data can sometimes lead you to wrong conclusions. Adjustment of the data prior to analysis may give you better insight.

Seasonally adjusting data

Data should be seasonally adjusted to remove any seasonal pattern before you try to interpret whether any particular value is unusually high or low.

Adjusting to constant dollars

A 1990 dollar was worth considerably more than a 2010 dollar, making it hard to compare prices in these two years.

Values described in dollars should be adjusted to 'constant' dollars using the consumer price index (CPI) or the price of some other 'standard' commodity. Using average income to adjust house prices to '1990 dollars',

Using per capita data

Looking at trends in 'quantity' values (e.g. a country's total alcohol consumption) is misleading over a period in which the population increases. It is more meaningful to examine quantities per person.

Always consider carefully whether a different variable would describe the data more meaningfully.