# Really Simple Statistics: Chi-Square #MRX

Welcome to Really Simple Statistics (RSS). There are lots of places online where you can ponder over the minute details of complicated equations but very few places that make statistics understandable to everyone. I won’t explain exceptions to the rule or special cases here. Let’s just get comfortable with the fundamentals.

If you haven’t had your morning cup of tea or coffee, may I be the first to disappoint you by saying this post has nothing to do with chai tea! Sorry. š¦

And my apologies again, it has nothing to with a traditional Chinese unit of length, or a dragon in Chinese mythology or a life-force.

### What is a chi-square

Chi-squares are all about percentages. They are a statistical test that is used to determine if the percentage for one group is significantly different than the percentage for another group. Is the percentage of men who play soccer different from the percentage of women who play soccer? Is the percentage of people who made a purchase on Saturday the same as the percentage of people who made a purchase on Sunday? Is the percentage of high-income people who buy Brand A the same as the percentage of low-income people who buy Brand A?

Like any statistic, chi-squares can be very simple.

• Compare the percentage of men who buy Brand A vs the percentage of women who buy Brand A

Chi-squares can also be more complicated.

• Compare the percentage of men who buy Brand A or Brand B or Brand C vs the percentage of women who buy Brand A or Brand B or Brand C

Most basic market research relies heavily on chi-square tests. All of those grid questions in a survey are usually analyzed with a chi-square – the percentage of people who chose “Strongly Agree” or the percentage of people who chose “Disagree.”

Usually, when a study is launched, one of the project deliverables is a set of data-tables, you know those 300 pages of tables? These tables are chock full of chi-square tests but you wouldn’t know it unless you read the tiny little print at the bottom of the tables.

The important thing to remember is that chi-squares all about percentages.

Really simple statistics!

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