GOF and Contingency Tables Intro
Channel: Profbsmith
Date: 2021-05-21

Uses two examples to introduce GOF and  CrossTabs (Contingency Tables). 
 
Example 1 uses expected proportions (therefore counts) of 4 species of fruit-flies vs observed, real-world counts.  Given 4000 fruit-flies, of the 4 species, the expected ratio is 1:3:3:9, or 250, 750, 750, and 2250.  What was observed was 226, 764, 733, and 2277. Are these proportions essentially equivalent, or is at least one species disproportionately represented? Another way to think about this GOF example: do the two data sets have the same distribution?

Example 2 uses Two-way (or Contingency) tables  to assess the independence of two variables.  Here, one variable is the natural herb, echinacea, and the other is infection status.  Echinacea is taken as the independent variable (the treatment or input), and infection status is the dependent variable (the output) since we're investigating whether infection status is dependent (contingent) on the treatment (independent).