Using Excel for IB Biology Statistics

General Rules:

If you number does not right justify (shift automatically to the right of the cell) then the computer did not recognize it as a number

If you put any letters into cells the computer will not recognize them as numbersDO NOT PUT UNITS IN CELLS with your quantitative data

Dont use Excel to make data tablesuse Word

Put similar data into columns

Put X values in the first column, Y values in the next column.

Use the toolbar to select additional changes to data

Use a scatter plot not a line graph when graphing linear data

Practice 0.5: Using Excel Formulas to Win Friends and Influence People

Simple Statistics: (when it says rangeput the cell number and letter separated by a colon)

=AVERAGE (range)calculates average of column/row range

=MEDIAN (range)calculates median of column/row range

=MODE (range) calculates mode of column/row range

=STDEV (range)calculates standard deviation of column/row range

1. Find the data from the image below entered in the Excel Practice 0.5 tab

2. Enter the equations into the appropriate cells to calculate the four statistical measures from above.

Graphing Data

1. Enter the data into columns

2. Select the data

3. Click on Chart from the menu bar

4. In Graph Type select the type you want. Choose Column for bar charts or XY scatter for line and scatter graphs. Do not choose line.

5. If you graph looks wrong you can correct it by clicking on the series tab and selecting the data you want (X and Y values)

6. In Chart Options select the choice that allows you to label the axes and have a title. You might also want the option that puts in a line of best fit (trend line).

7. You can also turn on and off gridlines and legends.

8. You can also add error bars by selecting Format Data Series. You want to choose custom error bars. Under both the + and select the STDEV for your data series. Sometimes error bars can be used to show what type of trend line better fits the data.

9. You can add trend lines by double clicking on any data point. Then select to add a trend line. You can decide what type of trend line you would like to add. You can also choose to add it in the Chart Options (step 6). The formula and correlation coefficient can also be added to the chart.

Practice 1: Recording and Plotting Data

1. Enter the data into Excel in the Practice 1 tab;

2. Recreate the graph shown below, including the following:

a. Creating an XY scatter plot (use the version with smooth lines and markers)

b. Labeling the X and Y axes as shown

c. Adding custom error bars using the CI (Confidence Interval) values

d. Inserting a linear trend line

Practice 2: Scatter Plot w/ Equation and R2

1. Find this data already entered in the Practice 2 tab

2. Recreate the graph shown below, including the following:

a. Creating an XY scatter plot (use the version with only points/markersno lines)

b. Labeling the X and Y axes as shown

c. Insert a linear trend line

d. Add an equation for the linear trend line (find this in trend line options)

e. Also display the R2 value for the linethis tells you what type of correlation there is in your data (strong positive is closer to 1, strong negative is closer to -1, and no correlation is 0)

Excel and the T-Test: The T-Test, as you have learned, is used to compare two sets of normally-distributed data and ultimately determine if the sets are significantly different. Using the T-Test formula in Excel (as in Practices 3 and 4), will output a direct P-Value. Remember that a P-value of 0.05 or less indicates significance (at least to 95% confidence).

There are two types of T-Tests which Excel can calculate; paired and unpaired data comparisons. Paired data sets come from the same sourcea common example of this would be comparing before and after data (see Practice 4). Unpaired data, which is more common for our uses, means the two data sets being compared come from two separate sources (such as the two species of hummingbirds being compared in the notes)this is shown in Practice 3.

Practice 3: Unpaired Data T-Test

1. Find the data already entered in the Practice 3 tab

2. Calculate the mean using the Excel average formula

3. Calculate the P-value using the T-Test formula for unpaired data:

=TTest (Range 1, Range 2, Tails, Type)

This gives the P directly

Tails: (either 1 or 2) In biology we generally want the two-tailed t-test, which tests for differences regardless of sign.

Type: (either 1 or 2). If the data is paired, meaning it is from the same individuals then the number is 1. If the data is unpaired; the sets are from two individuals, then the number is 2.

4. Create a bar graph of the two MEAN values

5. Label the X and Y axes

6. Add custom error bars based on the given 95% CI values

Practice 4: Paired T-Test Data

1. Find the data already entered in the Practice 4 tab

2. Calculate the mean using the Excel average formula

3. Calculate the P-value using the T-Test formula for unpaired data (see Practice 3)

4. Create a bar graph of the two MEAN values

5. Label the X and Y axes

6. Add custom error bars based on the given 95% CI values

Practice 5: Hey, wheres the picture??

1. Find the data comparing the masses of two species of bugs already entered in the Practice 5 tab

2. Calculate the MEAN and Standard Deviation (STDEV) in the appropriate cells using formulas

3. Create a bar graph of the means, including error bars that represent +/- 1 standard deviation