USING GRAPHING SKILLS

Axis While drawing graphs, we have two

axis.

X-axis: for consistent variables

Y-axis: for other variable

Graphs Line

Bar

Pie chart

…

Line graph It best shows the relationship between

two variables

Bar graph:Uses column to compare variables.

STATISTICAL ANALYSIS

The science of data

Statistics in Science Biological systems are subject to

environmental effects and genetic variation, therefore, they show differences from each other.

Similarities or differences between the organisms can be shown by using statistics.

How can we show similarities and differences?

egg radius of population x & y

x y

0

2

4

6

8

10

populations

radi

us (m

m)

What do error bars suggest?If the bars show extensive overlap, it is likely that there is not a significant difference between those values.

For this graph write down the systems showing overlap with rating zone.

How can we show similarities and differences?

egg radius of population x & y

x y

0

2

4

6

8

10

populations

radi

us (m

m)

Drawing error bars A way to draw an error bar is to use the

mean as the central point, and to use standard deviation as the end points of the error bar.

How do we calculate “Mean” & “Standard Deviation” ?

Firstly, some information…

•Mean: Average, central tendency of the data Also

• Median• Mode• Range

•Standard Deviation: spread of data around the mean.

How do we calculate “Mean” & “Standard Deviation” ?

EXAMPLE:How can leaf lengths be displayed graphically?

Simply measure the lengths of each and plot how many are of each length

If smoothed, the histogram data assumes this shape

This Shape? Is a classic bell-shaped curve, a Normal

Distribution curve.

The standard deviation is a statistic that tells you how tightly all the various examples are clustered around the mean in a set of data

A typical standard distribution curve

According to this curve: One standard deviation away from the

mean in either direction on the horizontal axis (the red area on the preceding graph) accounts for somewhere around 68 percent of the data in this group.

Two standard deviations away from the mean (the red and green areas) account for roughly 95 percent of the data.

Three Standard Deviations? three standard deviations (the red, green

and blue areas) account for about 99 percent of the data

-3sd -2sd +/-1sd 2sd +3sd

How is Standard Deviation calculated?

With this formula!

AGHHH! HOCAM

DO I NEED TO KNOW THIS FOR THE TEST?????

Not the formula! This can be calculated on a scientific calculator OR…. In Microsoft Excel, type the following code into the

cell where you want the Standard Deviation result, using the "unbiased," or "n-1" method: =STDEV(A1:A30) (substitute the cell name of the first value in your dataset for A1, and the cell name of the last value for A30.)

OR….Try this! http://www.pages.drexel.edu/~jdf37/mean.htm

Comparison of two sample means and St. deviations

http://click4biology.info/c4b/1/stat1.htm

A sample with a small standard deviation suggest narrow variation but a second sample with a larger standard deviation suggests wider variation.