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  • 00:00

    SPEAKER 1: Epidemiological curves.[CREATE] What are they, how do you make them,and how do you interpret them?[EPIDEMIC CURVES] This is the first of a two part videoseries.In this video, I'm going to talk about how to createan epidemiological curve.I'll tell you a little bit about whatthey are, as well, of course.And then in the next video, I'm going to tell youhow to interpret them.So remember, an epidemiological curveis a graphical or visual representation

  • 00:22

    SPEAKER 1 [continued]: of the onset of illness of cases in an outbreak.So the y-axis is the number of cases.The x-axis is the time interval during whichthe outbreak occurs.So at some point in time, our population of interestis exposed to a hazard.Now, we're talking about infectious disease,but remember, it doesn't have to be infectious disease.It could also be a chemical, a hazard.It could be radiation.But for the sake of these videos,

  • 00:44

    SPEAKER 1 [continued]: we're going to be talking about infectious disease.So after a period of time, and wecall that the incubation period, people start becoming ill.And that's when they start being represented on the epi curve.And, we represent them by a little blockon the timeline at the time interval when they became sick.And for people that became ill within the same time frame,their little blocks get stacked on top of each other.These stacks become columns.

  • 01:04

    SPEAKER 1 [continued]: And over time, these columns begin to take a shape.And we're going to be talking in the next video about howto interpret those shapes.But for now, let's take a look at Microsoft Excel.And look at how it is that you can create an epi curve.OK.Welcome to Microsoft Excel.I'm going to show you how to use Microsoft Excel to count upthe number of cases that became unwell in a particular week.

  • 01:25

    SPEAKER 1 [continued]: And draw an epi curve with that.OK, so.What we've got here, is we've got a makeshift line listing.Each case is represented by a row.And what we're going to do, is we're going to ask,how many cases there were in any given week.The first thing I'm going to suggest we do,is we're going to give this variable a name.To select the variable, go to the top.Push, shift, control, down.

  • 01:47

    SPEAKER 1 [continued]: Selects all the data.You give it a name at the top, on the left over here.We're going to call it, week.Enter.We're going to do the same thing with six.Shift, control, down.Use shift, command, down, if you're on a Mac.Give that a name.Call it, six.The reason we're interested in the week

  • 02:08

    SPEAKER 1 [continued]: that a case became unwell, is because the weeksare our time interval that we're going to use on epi curve.And the reason I've used six, is because I'm actuallygoing to divide the data up into male and female cases.The next thing we're going to do,is we're going to turn this into a table.And, you might think this is already a table.Actually, as far as Excel is concerned,it's not really a table yet.We need to tell Excel that this is a table.

  • 02:29

    SPEAKER 1 [continued]: The reason we do that, is so that if we get additional casesas this outbreak continues, and we add additional rowsat the bottom of the tables, those variablesthat we've just named will automatically expand with that.And that means, that our epi curve will automaticallyupdate itself.So to make it a table, go the top left hand corner.Again, shift, control, to the right.

  • 02:51

    SPEAKER 1 [continued]: Shift, control, down.That selects all the data.Simply go to Insert.And, voila.It's a table.One little thing, is we want to go down here.And it says, my table has headers.And we'll say, OK.The next thing that we're going to do,is we're going to organize our dataso that we can draw the epi curve.To do that, its going to a new sheet.Our x-axis is going to be weeks.So we need a value in one of these columns for weeks.

  • 03:14

    SPEAKER 1 [continued]: So let's just make a column of weeks.So we just go one, two, three.And drag that down.The next column, we're going to call, cases.And in the first example that I'm going to show you,we're just going to count the number of cases in any givenweek.And to do this, we use the COUNTIF function.So, let me show you how that works.We simply say, equals COUNTIF, open brackets.

  • 03:35

    SPEAKER 1 [continued]: And you'll see, Excel actually tells us what it wants.The first thing that it wants, is the range.And that's what we've already called, week.So we type in the word week, and put a comma.The next thing it wants, is a criteriaand what we wanted to count within that range of weeks.At first, it's just week one, close brackets, enter,and voila.As we expected, there are no cases in week 1.

  • 03:57

    SPEAKER 1 [continued]: If we click on this little dot at the bottom right handcorner of that cell, it's going to copy the formulaall the way down.We now have all the data that we need to draw our epi curve.To draw the epi curve, let's select the data.So it's shift, control, to the right, and down.Our data is selected.We go to insert and columns, and here is our epi curve.

  • 04:18

    SPEAKER 1 [continued]: I'm not going to neaten this one up.I'm actually going to do another epi curve,and then I'm going to show you how it isthat you should present them.For our next epi curve, what I'm going to dois going to divide the cases into males and femalesbecause we might be interested in howthis outbreak is unfolding.What's driving it?What population is most affected?And it doesn't have to be males and females.You could have confirmed cases and probable cases.

  • 04:39

    SPEAKER 1 [continued]: You could have what country they come from,et cetera, et cetera, et cetera.We're just going to use males and females as an example.So I'm going to type in the word male, here.And the word female, there.Now we're going to use the COUNTIF function again.But this time, it's going to be COUNTIFs, with an s at the end.Plural.Because there's more than one criteria that it'sgoing to look at.It's going to ask the question, how many cases were in week 1?

  • 05:01

    SPEAKER 1 [continued]: And how many of those were male?And it's going to come up with an answer,and pop it in that cell.So, equals.COUNTIFS, with an s at the end.Plural.Open brackets.The first range we're going to look at, again, is week.Comma, what is it going to look for in week?Well, we're going to look for this value here, 1.Then, just, comma.The second range it's going to look for, is, in the datathat we called six, we gave that a name earlier.

  • 05:23

    SPEAKER 1 [continued]: And, what is it going to look for in that data?It's going to look for this word over here, male.Close brackets.Enter.And as we suspected, there are 0 males that became symptomaticin week 1.Now, we can't just drag this formula down, and to the right,yet.If we did that, it would be dragging not only the cellinto which it was going to place the answer,but it would also drag the cells that it's referring to.

  • 05:45

    SPEAKER 1 [continued]: So, we need to do one or two things justto make sure that this works.And I'll show you how to do that.If we click on the cell, we can see the formula.In this formula, we can see this little A2 here,is referring to the blue cell there.And the B1, is referring to the red cell there.When we drag this formula across to the female column,we don't want this blue box to suddenly startlooking in column B. We want it to stay in column A.

  • 06:07

    SPEAKER 1 [continued]: So we put a little dollar sign in front of the A.And similarly, when we drag the formula down,we didn't want this red box just suddenlystart looking in row 2.We want it to stay in row 1.So we put a dollar sign in front of the 1.Enter.Now we can drag the formula across.And again, click on the little box at the bottom right.And we've got all the data we need for our epi curve.

  • 06:29

    SPEAKER 1 [continued]: To draw the epi curve, simply control, shift, to the right.And down.All the data is selected.Go to insert.Now, we want to select stacked columns.Here's our epi curve, but I'm going to show youhow to neaten that up.The first thing we're going to do,is we're going to put this into a sheet of its own.So go to Move Chart.Say, New Sheet.And let's give that a name.And, voila.We're in a new sheet.

  • 06:49

    SPEAKER 1 [continued]: There's a couple of things we cando to make this even better.What we want to do, is we want to add a few elements.For example, we want to add axis titles.Horizontal and vertical.So let's do that.We want our legend to be nice and neatly on the right.And it's quite nice to get rid of the gaps.Your title needs to include what disease you'retalk about, what time frame you're talking about,and what location this all happened in.

  • 07:13

    SPEAKER 1 [continued]: And, voila.We have an epi curve.Thank you for watching.I hope you found that useful.Have a great day.

Video Info

Series Name: Gregory Martin

Episode: 6

Publisher: Gregory Martin

Publication Year: 2016

Video Type:Tutorial

Methods: Epidemiology, Graphs, Population parameters, Population variance, Data synthesis, Data visualization, Data analysis skills

Keywords: charts (data visualization); data visualisation; epidemiologic data; epidemiological concepts; epidemiology; graphical presentation of data; infectious disease; outbreak investigation; tabular data ... Show More

Segment Info

Segment Num.: 1

Persons Discussed:

Events Discussed:

Keywords:

Abstract

Greg Martin, Editor-in-Chief, Globalization and Health, discusses and provides an example of how to create an epidemiological curve in Excel.

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How to Create an Epidemiological Curve

Greg Martin, Editor-in-Chief, Globalization and Health, discusses and provides an example of how to create an epidemiological curve in Excel.

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