Introduction

Accessing StatCalc

Overview

StatCalc appears on the Epi Info™ 7 main menu, middle row, right column, and captioned "Statistical calculators for sample size, power, and more."  Selecting the StatCalc button opens the StatCalc menu, which is similar to the main menu in appearance, and contains buttons for the eight (8) StatCalc calculators listed in TABLE NAME + LINK, below.  The individual calculators are also part of Visual Dashboard (VD).  They can be accessed from the Options menu, under the "Add StatCalc calculator" submenu, and added to the dashboard Canvas in the same manner as other gadgets.

Functional Requirements

1. Epi Info™ 7 shall enable the user to open the StatCalc menu from the Epi Info™ main menu.
2. The StatCalc menu shall enable the user to start the eight (8) StatCalc calculators from an array of buttons bearing the names of the calculators.
3. When the user selects a calculator from the StatCalc menu, each calculator shall open a window containing the components specified in TABLE NAME + LINK, below.
4. The VD shall enable the user to select StatCalc calculators from the Options menu.
5. The VD shall enable the user to place the selected calculators on the Canvas
6. Calculators placed on the dashboard Canvas shall have all the relevant properties of other gadgets including the ability to:
   1. be repositioned on the Canvas,
   2. anchor to other gadgets,
   3. stack vertically with other gadgets in response to the user pressing the Vertical Arrange button on the VD status bar,
   4. hide its borders in response to the user pressing the Hide Gadget Borders button on the VD status bar^[1],
   5. collapse and expand the calculator window in response to the user pressing the Arrow toggle button on the gadget's title bar^[2], and
   6. close and be removed from the canvas  in response to the user pressing the Close button (red box with a white × inside).

Notes:

1. The behavior of this function on StatCalc calculators differs from that of other gadgets.  In most cases, the Hide Gadget Borders button not only removes the outer rectangle, but the title bar and associated buttons as well.  As a consequence, the gadgets can no longer be repositioned, reconfigured, collapsed or expanded, or closed.  The only thing the Hide Gadget Borders button does to a StatCalc calculator is remove its border.
2. These functions have not been implemented as of Epi Info™ version 7.2.0.1.  See also Future Development.

StatCalc Calculators

Overview

The StatCalc calculators can be divided into three general categories: 1). Sample size and power calculations, 2).  Two-way table calculations, and 3). Distribution-based event probabilities.  Each group has its characteristic input parameters and analyses but they all provide the user with the ability to enter hypothetical data and evaluate their statistical significance.  In doing so, the user may determine important study parameters such as the number of subjects required to test a hypothesis given specific assumptions about variables such as rates of exposure or the ratios of cases to controls.

Functional Requirements

The requirements for StatCalc are best described in a tabular format, with a row for each calculator and a column for each feature, such as titles, labels, and descriptive text, or property category, such as input parameters and the headings for values derived from the input values.

StatCalc Calculator Properties

Notes:

1. Anchor
   t1n1 t1n1

   Not all input parameters are independent.

2. Anchor
   t1n2 t1n2

   Extended Mantel-Haenszel

Future Development

Functional Requirements

In the following list, each numbered item represents the name of a StatCalc tool as it appears in the main menu of the stand-alone module or the Options→Add StatCalc Calculator submenu in Visual Dashboard.  The secondary (lettered) list items contain labeled elements of user interface such as titles and descriptive text, input parameters (count) and the heading for derived values, the values calculated from the input values.  The most deeply nested items are typically the specific input parameters, derived values and summary results, themselves, organized in a hierarchy appropriate for the specific tool.

1. Population Survey
   1. Title: Sample Size and Power
   2. Description: Population survey or descriptive study
   3. Note: For simple random sampling, leave design effect and clusters equal to 1.
   4. Input Parameters:1
      1. Population size
      2. Expected frequency
      3. Acceptable Margin of Error
      4. Design effect
      5. Clusters
   5. Derived values
      1. For confidence levels of 80%, 90%, 95%, 97%, 99%, 99.9%, and 99.99%
      2. Cluster size
      3. Total Sample
2. Cohort or Cross-Sectional
   1. Title: Sample Size and Power
   2. Description: Unmatched cohort and cross-sectional studies (exposed and non-exposed)
   3. Note: n/a
   4. Input parameters (not all parameters are independent):
      1. Two-sided confidence level (choices: 80%, 90%, 95%, 97%, 99%, 99.9%, and 99.99%)
      2. Power (%)
      3. Ratio (Unexposed : Exposed)
      4. Percent outcome in unexposed group (%)
      5. Risk ratio
      6. Odds ratio
      7. Percent outcome in exposed group (%)
   5. Derived values:
      1. Exposed, unexposed, totals
      2. for Kelsey, Fleiss and Fleiss w/CC Model
3. Unmatched Case-Control
   1. Title:  Sample Size and Power
   2. Description: Unmatched case-control study (Comparison of ILL and NOT ILL)
   3. Note: n/a
   4. Input parameters (not all parameters are independent):
      1. Two-sided confidence level (choices: 80%, 90%, 95%, 97%, 99%, 99.9%, and 99.99%)
      2. Power (%)
      3. Ratio of controls to cases
      4. Percent of controls exposed (%)
      5. Odds ratio
      6. Percent of cases with exposure (%)
   5. Derived values:
      1. Cases, controls, totals
      2. for Kelsey, Fleiss and Fleiss w/CC Models
4. Chi-square for Trend
   1. Title: Chi-Square for Trend
   2. Description: Analysis for Linear Trends in Proportions
   3. Note: n/a
   4. Input parameters
      1. series of records containing the following values: exposure score, cases, controls
   5. Derived values
      1. odds ratio (by record)
      2. Chi square for linear trend (Extended Mantel-Haenszel)
      3. P-value
5. Tables (2 x 2 x N)
   1. Title: 2x2 Tables
   2. Description: n/a
   3. Note: n/a
   4. Input parameters, by stratum, 1 - 9:
      1. Subject count: Exposure , Outcome 
      2. Subject count: Exposure , Outcome 
      3. Subject count: Exposure , Outcome 
      4. Subject count: Exposure , Outcome 
   5. Derived values
      1. By stratum
         1. Odds-based Parameters
            1. Odds Ratio: Estimate, Lower, Upper
            2. Maximum Likelihood Estimate Odds Radio (Mid-P): Estimate, Lower, Upper
            3. Fisher's Exact Test: Lower and Upper
         2. Risk-based Parameters
            1. Risk ratio: Estimate, Lower, Upper
            2. Risk difference: Estimate, Lower, Upper
         3. Statistical Tests
            1. Uncorrected: chi-square, 2-tailed P-value
            2. Mantel-Haenszel: chi-square, 2-tailed P-value
            3. Mid-P exact test: 1-tailed P-value
            4. Fisher's exact test: 1-tailed P-value, 2-tailed P-value
      2. Summary results
         1. Odds ratio
            1. Crude (Cross Product): Estimate, Lower, Upper
            2. Crude (Maximum Likelihood Estimate): Estimate, Lower, Upper
            3. Fisher's Exact test: Lower and Upper
            4. Adjusted (MH): Estimate, Lower, Upper
            5. Adjusted (Maximum Likelihood Estimate): Estimate, Lower, Upper
         2. Risk Ratio
            1. Crude: Estimate, Lower, Upper
            2. Adjusted: Estimate, Lower, Upper
         3. Chi-Square
            1. Uncorrected (MH): chi-square, (1-tailed P-value), 2-tailed P-value
            2. Corrected (MH):  chi-square, (1-tailed P-value), 2-tailed P-value
6. Matched Pair Case Control Study
   1. Title: Pair-Matched Case-Control Study
   2. Description: n/a
   3. Note: n/a
   4. Input parameters
      1. Cases: Exposure 
      2. Cases: Exposure 
      3. Controls: Exposure 
      4. Controls: Exposure 
   5. Derived values:
      1. Odds-based parameters
         1. Odds Ratio: Estimate, Lower, Upper
         2. Exact: Lower and Upper
      2. Statistical Tests
         1. McNemar: chi-square, 2-tailed P-value
         2. Corrected: chi-square, 2-tailed P-value
         3. Fisher's exact test: 1-tailed P-value, 2-tailed P-value
7. Population Binomial (Proportion vs. Std.)
   1. Title: Binomial
   2. Description: Binomial - Proportion vs. Standard
   3. Note: n/a
   4. Input parameters:
      1. Numerator
      2. Total observations
      3. Expected percentage
   5. Derived values
      1. Probability that the number of cases is <, <=, =, >=, > numerator
      2. Two-tailed P-value
      3. 95% confidence interval
8. Poisson (Rare Event vs. Std.)
   1. Title: Poisson
   2. Description: Rare Event vs. Standard
   3. Note: n/a
   4. Input parameters
      1. Observed number of events
      2. Expected number of events
   5. Derived values
      1. Probability that the number of events found is <, <=, =, >=, > to the observed number

Overview

Overview

The StatCalc tools are well-implemented from the mathematical and performance points of view.  The primary problem involves the labeling of fields and the limited documentation of specific tools.  Generally speaking, the calculators are designed with a very specific application in mind, while the underlying calculations may be applied to a much broader set of problems.  This can be addressed in a number of ways.  Making the labels more general may be helpful for some users.  However, a better approach might be to add a pull-down menu to tools such as "Cohort or Cross-Sectional" that offers a number of possible scenarios.  In this case, the options may include "Unmatched Cohort Study" and "Cross-Sectional Study".  Choosing an option would change the labeling of the input (and some output) fields to use terminology traditionally associated with that study type.  The options may also reflect the methodological context of the study.  Applied to infectious disease, one examines the ratio of exposed to unexposed individuals and the corresponding numbers who are ill or unaffected.  In contrast, a genetic study examines individuals that do or do not possess a particular allele of a gene or marker; the outcome is expressed in terms of phenotypes.  The goal is to express the statistical variables in a manner that is familiar to the researcher using a particular study design in a particular discipline.  Doing so will help ensure that the user enters the proper information in the correct fields and can accurately interpret the results.

The remaining issues concern consistency in how the tools are named and referred to in different parts of Epi Info™.  The label on the button in the StatCalc menu or VD Options menu does not always match the labeling of the resulting window or gadget (when run in stand-alone mode or as part of Visual Dashboard, respectively).  There is also inconsistent hyphenation of compound adjectives (e.g., "case-control").  Finally, the StatCalc gadgets in VD do not follow the pattern for the control widgets (located in the upper-right corner) used in other VD gadgets (they cannot be collapsed, for example).