A student asked why direction of an association would reverse when you add a potential confounder. I returned this illustration.
In this hypothetical example, for both men and women eating more low calorie foods is associated with a lower BMI. However, if men eat more low cal food and have higher BMI then the combined association reverses.
So now we are giving billions of dollars to the automotive industry. With this money they will come up with some new efficient car designs and do all the navel-gazing they need to become strong companies once again. Soon people will leap at the chance to buy a new GM car.
What was lost in the stock market crash of October, 1929? "Still, most academic experts agree on one aspect of the crash: It wiped out billions of dollars of wealth in one day, and this immediately depressed consumer buying." - http://query.nytimes.com/gst/fullpage.html?res=9B0DE4DC1F3BF932A15753C1A961948260&sec=&spon=&pagewanted=2
TEXT/DOCUMENTS
E.g. Microsoft Word
One dimensionsal - just a list. You can create tables, but that is like creating multiple columns - it is still a list, just broken into columns for convenience.
SPREADSHEETS
E.g. Microsoft Excel
Two dimensional - rows and columns. In some sense Excel recognizes that a column belongs together and a row belongs together. For example, a row may be a name and a set of grades for that person. The first column would then be the names of students in a class, the second column their scores on Quiz 1, etc.
RELATIONAL DATABASES
E.g. Microsoft Access, FileMaker
Concept 1: Three dimensional - rows, columns and pillars. (Picture to come.) Take the Excel example and go to the last column - final score. Then add a pillar coming out of each cell, representing the final grade. This pillar can take values from A to F, and slides up or down until the appropriate grade is in the underlying Excel spreadsheet.
Concept 2: Databases have spreadsheets as their underlying data. Think of that as not a flat piece of paper but as a bunch ob boxes, all lined up in rows and columns. The database allows you to create different views of that spreadsheet - it is like a cardboard you can cut out so when you set it on the boxes you only see what you choose to see.