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IB: ENVIRONMENTAL SYSTEMS AND SOCIETYIB: BIOLOGY

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Statistics in Excel

This works sheet refers to the Excel workbook: Statistics in Excel

The set of data in the table is like the sort of data which is often generated in a biological experiment. 2 Sets of data (2 separate conditions) repeated 8 times (a-g). Once some measurements have been collected the first job is usually to summarise them using descriptive statistics. Excel can make this very easy.

In the table: mean, range, variance, Standard Deviation and Standard Error of the mean have been calculated for the data Set 1.

Each step below walks you through doing this for Data Set 2. Follow each step and do not try to jump ahead.

You will be entering formula directly into Excel cells, not using the function keys but doing it the long way around. This will help you understand much more what is happening.

First you need to understand what a cell reference is:

The first top left hand corner cell has the cell reference A1

Click your cursor into Cell D1 and type =A1 then press return

D1 now says exactly what A1 says: Repeats

=A1 is a cell reference it allows a function to happen in the cell D1 based on a condition in Cell A1 everything you are going to do is based on this idea

Task one: Calculating a mean

1. Click your cursor into cell C9 then enter =Average(C2:C7) then press return

2. Excel uses the term average instead of mean but what you have done is tell excel to calculate the mean of the cells in the column sequences from C2 to C7 putting a colon between 2 cell references forces excel to use the data between those two references

Task 2: Calculating the range

1. Click in C11 and enter = MAX(C2:C7)-MIN(C2:C7) and press return

2. This time you have told excel to calculate the difference between the maximum value and the minimum vlue in the sequence

Descriptive Statistics

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Task 3: Calculating Variance

1. In C13 enter = VAR(C2:C7)

2 Variance is not a very useful statistic on its own but is often used as part of other calculations so it is worth knowing how to calculate it.

Task 4: Standard Deviation (SD): SD is a common and fairly easy to calculate statistic, even by hand. However it is not the best statistic to use when comparing different sets of data. This is especially true of the data sets are different sizes

1 in C15 enter = STDEVC2:C7)

Task 5: Standard Error of the Mean (SEM)

1 in C17 enter = STDEVC2:C7)/SQRT(COUNT(C2:C7))

2 This gives an indication of the confidence of the mean, and is often used as an error measurement simply because it is small rather than for any good statistical reason.

When you have finished you should have a spreadsheet which looks like this: apart from the comment boxes

When you have finished move on to Part 2

IB: ENVIRONMENTAL SYSTEMS AND SOCIETYIB: BIOLOGY

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Part 2

Naming the ink color of color words can be difficult. For example, if asked to name the color of the word "blue" is difficult because the answer (red) conflicts with the word "blue." This interference is called "Stroop Interference" after the researcher who first discovered the phenomenon.

This case study is a classroom demonstration. Students were each given three tasks. In the "words" task, students read the names of 60 color words written in black ink; in the "color" task, students named the colors of 60 rectangles; in the "interference" task, students named the ink color of 60 conflicting color words. The times to read the stimuli were recorded. There were 31 female and 16 male students.

From: http://onlinestatbook.com/case_studies/stroop.html

Calculate the: Mean, Range, SD and SEM for each data set

When you have finished move onto Part 3 below

Part 3

First highlight the first two columns (x,y) in the tableThen click on the chart wizard (or Insert menu > Chart).

1 In Graph Type, choose ‘XY (Scatter)’ for line and scatter graphs. Do not choose ‘Line’, which plots the data against row number. This is a very common mistake.

2 Choose the graph type with data points only not with lines drawn. Click Next

3 Check that Columns is choose in data ranges. Click Next

4 Give the chart a title and label the x axis X Values and the y axis Y Values. Click Next

5 Place as an object in the sheet.

Now you are going to add error bars for SEM to your chart

6 Double-click on any data point or bar to get the Format Data Series dialogue box

7 Choose the Y Error Bars tab

8 Click the Custom + box

9 Highlight the range of cells containing the SEM data in the table. Then press OK

10 repeat for the custom -

You now have SEM error bars added to each data point

IB: ENVIRONMENTAL SYSTEMS AND SOCIETYIB: BIOLOGY

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