Demographics is the science of population statistics - a study of the styles, preferences, habits, and qualities of a particular demographic. As any statistically based science, it might be subject to some degree of bullshit. Demographics are frequently used in the formulation of public policy, and especially in advertising.
 Common demographic classes
Some of the common classes used in demographics for the categorisation of the population include, but are not limited to:
- Consumer habits
 Specific areas of bullshittery
Bullshitting by getting demographics wrong is easy enough. The two main problems are:
- Confusing a statistical trend with a rule. E.g., statistically, more men than women like football, therefore all men like football. We call this fallacy stereotyping - which is even worse when the "rule" isn't even backed up by the statistical evidence.
- Mistaking one statistical trend as applying outside the demographic. This is why medical trials always specify the status of the type of people they're looking at. You can't take a study that looked at 65 year-old men and assume you'll see the same medical benefits in healthy women in their 20s. Often referred to as the spotlight fallacy.
Between these two points, pretty much every misuse of demographic data can be found.
A cohort is the demographic concept of classifying individuals on the basis of the era in which they were born and/or the significant events that they have experienced. The definition of these are vague and vary to a certain degree but some examples include:
- Baby boomers
- Generation X
- Generation Y
A census is a regular attempt to count the number of people in an area or state, possibly so that resources (including politicians) can be distributed fairly. A census is also how quite a lot of data for demographic research is acquired.
Censuses are often slightly skewed - not everybody gets counted for various reasons, and there are usually quirks and 'some people' think it is a blasted liberty.
There is no indication that the census requiring Mary, Joseph, and yet-to-be-born Jesus actually occurred.