Quick Linear Regression8.2.1

In statistics, linear regression is a technique for estimating the relationship between an independent variable, X, and its scalar result, the dependent variable, Y, derived from a series of X-Y relationships.

The computational routine involves trying to fit a straight line between a scatter plot of X-Y coordinates such that the sum of the squared differences between each dependent outcome, Yi, and the line computed at each Xi is minimized. This is the so-called "ordinary least squares (OLS)" estimator.

R-squared, often called the "coefficient of determination," expresses the "goodness of fit" of the line to the scatter plot. It ranges from 0, no fit whatever, to 1, which is a perfect relationship where all the points in the plot fit along the straight line.

The iPad version allows you to add, retrieve, reorder, or delete data sets. It also permits emailing, text messaging, and printing of a PDF report. Also, changing the form of the regression equation from Y = function(X) to X = function(Y) is allowed along with estimation of the dependent variable amount from a user-specified independent variable amount.

Version History - Fixed bug that prevented app output from being shared from the iPad. 8.2.1 08/13/2023 - Minor change to graph engine CorePlot. 8.2 08/06/2023 - Updated graph to CorePlot version 2.4
- GUI changes 8.1 05/10/2023 - Redesign and reworking of GUI.
- Code changes to accommodate iOS 13.
- Removed links to Facebook and Twitter.
- Audio feedback when various objects are touched.
- Changed most decimal precision from single (float) to double. 8.0 12/23/2019 - Code tweaks to accommodate iOS 10. 7.5 11/30/2016 - Changed button action from "Touch Up Inside" to "Touch Down" for quicker performance.
- Code changes for simplification and improvement in logic. 7.4 06/14/2016 - Changes to adapt to iOS 9, mostly involving fonts. 7.3 09/30/2015 - New icons for buttons and other controls.
- In iPhone version, double arrows increment or decrement repeatedly if the touch down is held.
- Redesigned the app logo.
- Updated the Facebook link syntax. 7.2 05/21/2015 - Consolidated PDF report sharing options
- Added AirDrop as a report sharing option
- Added Facebook and Twitter posting 7.1 01/10/2015 - By convention, linear regression is expressed as Y = function(X) where Y is the dependent variable and X is the independent variable. The iPad version now allows expressing the linear regression as X = function(Y) as an option.
- Also, in the iPad version, you may estimate the dependent variable amount by entering an estimate of the independent variable.
- Minor GUI tweaks.
- Updated for iOS 8 and iPhone 6. 7.0 10/05/2014 - Bug fix affecting computation of numerically small X-Y pairs.
- Added correlation coefficient.
- Bug fix affecting iPhone version when loading the first Y value from the stored data with the slider input option. 6.2 06/12/2014 - Fixed bug that prevented adding a new data file without exiting app. 6.1 02/26/2014 - iPad version now adds email, text message, and print capability. A PDF report at a resolution of 72 dpi is available for sharing.
- Minor bug fix involving GUI interface. 6.0 02/12/2014 - Rewritten and redesigned for iOS 7.
- Added warning to prevent inadvertent resetting of all data in both iPhone and iPad versions.
- GUI enhancements. 5.0 12/11/2013 - Major revision that includes the option of adding data sets, retrieving saved sets, and deleting or reordering the saved sets. 4.0 08/15/2013 - In iPad version, the behavior of the "info" and "clear" buttons have been modified to avoid unanticipated behaviors. Also, crashes resulting from touching the "+/-" button when the keyboard was displayed have been eliminated.
- Clearing data now works properly. 3.3 03/28/2013 - Streamlined source code for improved performance. 3.2 02/26/2013 - Added a +/- stepper for adjusting number of pairs to regress.

- Bug fix for iOS 5.

- Minor GUI changes. 3.1 02/07/2013 - Quick Linear Regression is now a Universal app.

- The iPad version allows selection of the number of X-Y pairs to be regressed between 3 and 20.

- The iPhone version modifies the way data entry fields are cleared by putting a "Clear" button above the numeric keypad. 3.0 01/24/2013 - To simplify moving between the two methods of data entry, we have added buttons for "Keypad" and "Slider" in the lower right-hand corner of the data entry views.

- On the 'Extended Regression' view, we added a reminder that a data entry of zero is a number, but a blank data entry is an 'n/a' that removes the x-y pair from the regression computation. 2.3 10/10/2012 - Never mind. Removed upside-down portrait mode that caused display issues when editing.

- Modified syntax of iTunes App Store link. 2.2 09/26/2012 - Added ability to create values with zero to three decimal place precision in the 'Keypad Input' screen and changed the way that numbers are assigned plus or minus signs.

- Extended the number of x-y pairs from 18 to 20 in the 'Keypad Input' screen.

- In 'Keypad Input', removing a data entry with the 'n/a' description is accomplished by making the entry blank.

- Improved floating point precision of all calculations from single to double.

- Minor GUI changes. 2.1 08/27/2012 - Added new page for 'keypad' data entry beyond the -1000 to +1000 numerical limits of the 'slider' data entry
- Added 'Previous Item' button on slider data entry view for backward movement among data entry fields
- Various display modifications 2.0 04/09/2012 1.0 12/15/2011