EPITOOL v. 1.0
STATISTICS APPLICATION FOR PALMPILOT
Overview
EPITOOL is a powerful
application for epidemiologists and medical specialists to use their PalmOS
devices (Palm Pilot, Handspring, etc.) to determine statistics concerning
disease control and outbreaks. Epitool was conceived by Dr. Carolyn Masters-Williams
and developed by Intranet Solutions, LLC through the support of the Johns
Hopkins Hospital department of Healthcare Epidemiology and Infection Control.
Creating studies within EpiTool
consists of two steps. When you first
start the application you will see a list of previously entered studies. To continue a study (i.e. enter new strata
or edit study data or existing strata) tap on its name in the list. If you would like to enter a new study, tap
on the “New” button at the bottom of the page.
If you would like to see information about the application including the
copyright holder, programmer, or how to get more information, tap on the
“About” button.
When you first create a study you
will have some generic information filled in.
You can tap on any of the areas and edit the information to suit your
specific case. If you would like to
change the creation date from the default of the PalmPilot’s current date, tap
on the “Date Created” field. This will
bring up the standard PalmPilot Calendar.
You can then tap on your preferred date.
If you have entered strata for this
study already, you will see them listed in the box above the buttons. To edit a strata, tap on its name in the
list. To add a new strata to this
study, tap on the
“+
Strata” button. You will move to the
strata information page.
If you would like to completely
delete a study from your database, you can tap on the “Delete Study”
button. This will completely and permanently remove the displayed study
including all strata. If this is
what you want to do, answer “yes” to the warning prompt. You will move back to the List of Studies
form.
Once you have chosen a strata name
(or tapped on the “+ Strata” button) you will see detailed information. You may change the strata name, or any of
the values in the 2x2 table. Once you
have entered all 4 values, you will see the Odds Ratio and Relative Risk fields
update. Note: If you edit one of the values in the table, you must move out
of that field to update the Odds Ratio and Relative Risk displays.
If you would like to delete a strata
from a study, you can do this by tapping on the “Delete Strata” button. As with the study delete, there is no undo
function.
If you would like to see a more
detailed analysis for this strata, tap on the “Analysis” button. This will take you to a screen showing a
more in-depth analysis of your data.
To determine the p-value a table
look-up is used. Below the “p-value
(From table)” line are the Chi Square table values that straddle the calculated
Chi Square value and their associated p-values. For example, in the table shown at right, the Chi^2 value
calculated was 0.117 which is between 0.1 and 0.45. A Chi Square value of 0.1 matches a p-value of 0.75 and a Chi
Square value of 0.45 matches p-value 0.5.
CALCULATED
VALUES
|
O1 |
O2 |
Top = O1/(O1+O2) |
|
O3 |
O4 |
Bottom = O3/(O3+O4) |
Relative Risk = Top/Bottom
Risk
Difference = Top – Bottom
Ldiag
= O1*O4
Rdiag
= O2*O3
Odds
Ratio = Ldiag/Rdiag
TopRow
= O1+O2
BottomRow
= O3+O4
LeftCol
= O1+O3
RightCol
= O2+O4
N
= TopRow + BottomRow
|
E1 = TopRow * LeftCol / N |
E2 = TopRow * RightCol / N |
|
E3 = BottomRow * LeftCol / N |
E4 = BottomRow * RightCol / N |
Chi = (o1-e1-0.5)*(o1-e1-0.5)/e1 +
(o2-e2-0.5)*(o2-e2-0.5)/e2 +
(o3-e3-0.5)*(o3-e3-0.5)/e3 + (o4-e4-0.5)*(o4-e4-0.5)/e4
P-Values are looked up in a table
APPLICATION
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