using excel biostatistics 212 lecture 4. housekeeping finish lab 2 today and/or start lab 3 mac...
TRANSCRIPT
Housekeeping
• Finish Lab 2 today and/or start Lab 3
• Mac Addendum
• Copying and pasting from Stata
Today...
• Why are we talking about spreadsheets?• Pro’s and Con’s of using a spreadsheet for:
– Data management, Statistics, Calculating, Modeling, Tables, Figures
• Cells• Formulas• Cutting and pasting formulas• Spreadsheet style• Examples
Why spreadsheets?
• Excel is very popular, and very useful– Store numbers and text– Calculations– Desktop graphics – Tables and Figures– Flexible creation of ledgers, models, other
complex programs
Why spreadsheets?
• How is a spreadsheet different than Stata’s data editor?– Less structured– Formulas– Formatting
Why spreadsheets?
• How is a spreadsheet different than a database program like Access?– Less structured– Formula chains– Formatting
Pro’s and Con’s of spreadsheets
• For data management– Pro’s
• Easy start – just name columns and start typing
– Con’s• No structure• Can’t sort or query data• Can’t generate new variables• “Flat” file – no relational table structure allowed
Pro’s and Con’s of spreadsheets
• For statistical analysis– Pro’s
• Easy start, if you know how to do formulas
– Con’s• Extremely limited range of options
• Difficult to document
Pro’s and Con’s of spreadsheets
• For calculating, or “modeling”– Pro’s
• Repetitive calculations easy
• Complex calculations easy
– Con’s• Simple, 1-time calculations not as fast
• Sometimes hard to decipher in retrospect
Cells
• The basic building block of a spreadsheet
• Can contain:– Numbers– Text– Dates, times, other special formats– “blanks”
• start with 230 x 66536 = 15.3 million blank cells
Cells, cont
• Enter anything you like into each cell (numbers, text, symbols, etc) using keyboard
• Contents displayed on spreadsheet
• Organized and named by column/row
Formulas
• Use when you want the contents of one cell to depend on the contents of other cells
•ALWAYS starts with: =
(an “equals sign”)
Formulas
• Can contain:– Numbers– Text– References to cells– The usual math operators (+ - * / ^ )– Built-in functions
Formulas
• Cell contents update automatically when a referenced cell content changes
• “Chains” of formulas make for flexible calculating
Formulas
• Contents of a cell displayed on spreadsheet
• The formula determining that content is displayed in the “formula box” (term?)
• Example
Formulas
• Types of formulas– Arithmetic
• +, -, *, /, ^
– Logic• IF(boolean, value 1, value 2)
– Returns value 1 if TRUE, value2 if FALSE
• AND(boolean, boolean, boolean…)– Returns TRUE if all booleans are true, otherwise FALSE
• OR(boolean, boolean, boolean…)– Returns TRUE if any booleans are true, otherwise FALSE
Formulas
• Types of formulas, cont– Functions, for example:
• SUM(range of cells)– Returns the sum of the values in the range
– SUM(A5:A10)
• AVERAGE(range of cells)– Returns the average of the values in the range
• STDEV(range of cells)– Returns the standard deviation
• NORMINV(probability, mean of dist, SD of dist)– Returns the z-value associated with a given probability…
Formulas
• Types of formulas, cont– Functions, for example:
• LN(number)– Returns the natural log of a number
• ABS(number)– Returns the absolute value of a number
• LEFT(text, number of characters=x)– Returns x number of characters from the text in the cell, starting
at the left side…
• NOW()– Returns the current date, time
Cutting and pasting formulas
• Excel assumes the cell references are ABSOLUTE, and you’re just moving the location of the formula cell
• Example
Copying and pasting formulas
• Excel assumes the cell references are RELATIVE
• Shortcut (drag little square)
• Example
Copying and pasting formulas
• If you want to FIX the position of a referenced cell, use $’s= A5 + $B$6
• Example
Examples
• Repetitive calculations– Back-transforming linear regression coefficients
• Complex calculations– 2 x 2 template
• Modeling– Mortgage calculator– Risk integrator
Spreadsheet style
• For models:– Inputs on the left, in red– Outputs on the right, in blue, boxed, bolded, etc– Calculations on other sheets– “Protect” all cells besides inputs
• Format/Cells…/Protection
• Tools/Protect
Lab 3
• Practice with:– A repetitive calculation spreadsheet
– A complex calculation spreadsheet
– Introduction to making a figure with Excel
• Extra credit puzzle challenge – 2x2 excel template
• Due 10/25/05