The stack displays only 4 items at once, but one can scroll up and down the stack by clicking on the up and down arrow above the stack. The stack is a feature of the calculator that provides a way to view a history of results. The user is given the option to use either input method and both are equally valid however, there are some trigonometric function (as noted below) that are limited to computer keyboard entry only since there is a limited amount of space available for graphical button placements. The online calculator supports data entry through either a graphical button or through the use of traditional computer keyboard keys. Expressions that contain parenthesis, such as "(1+2)*3", are evaluated by noting the precedence order and entering the form as "1 2 + 3 *". For example, to evaluate the expression "1 + 2" in RPN, the user is required to enter "1 2 +" and the expression is evaluated immediately after the operator. RPN Mode RPN, which stands for Reverse Polish notation, is a stack-based notation where operators are designed to follow their operands. Expressions entered in algebraic input mode are done in a manner that closely resembles the natural form of the expression and the order of the operations is determined by operator precedence and parenthesis. The calculator mode is set by clicking on the "ALG/RPN" symbol in the status bar or by changing the mode inside the menu dialog box.Īlgebraic input mode is commonly referred to as "infix notation" and is widely used by most handheld calculators. The online calculator operates in either algebraic input (default mode) or RPN input. eCalc is offered as both a free online calculator and as a downloadable calculator. Inverse Cotangent Online Hyperbolic Trigonometric FunctionsĬoordinate System Decimal To Fraction Complex Numbers Online Unit Converter Constants Library Online Solver Base ConverterĮCalc is a free and easy to use scientific calculator that supports many advanced features including unit conversion, equation solving, and even complex-number math. To calculate the post-hoc statistical power of an existing trial, please visit the post-hoc power analysis calculator.Windows Version Mac OSX Version View More Downloads Most medical literature uses a beta cut-off of 20% (0.2) - indicating a 20% chance that a significant difference is missed. Beta is directly related to study power (Power = 1 - β). Beta: The probability of a type-II error - not detecting a difference when one actually exists.Most medical literature uses an alpha cut-off of 5% (0.05) - indicating a 5% chance that a significant difference is actually due to chance and is not a true difference. Alpha: The probability of a type-I error - finding a difference when a difference does not exist.Treatment Effect Size: If the difference between two treatments is small, more patients will be required to detect a difference.Population Variance: The higher the variance (standard deviation), the more patients are needed to demonstrate a difference.Baseline Incidence: If an outcome occurs infrequently, many more patients are needed in order to detect a difference.Generally speaking, statistical power is determined by the following variables: Enrolling too many patients can be unnecessarily costly or time-consuming. By enrolling too few subjects, a study may not have enough statistical power to detect a difference (type II error). 1īefore a study is conducted, investigators need to determine how many subjects should be included. This calculator uses a number of different equations to determine the minimum number of subjects that need to be enrolled in a study in order to have sufficient statistical power to detect a treatment effect.
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