Error bars on graphs represent the variability or spread of data by showing the standard deviation or range. A normal distribution is a bell-shaped curve where the most frequent data points fall in the center. The standard deviation measures how spread out data points are from the mean and 68% of values fall within one standard deviation of the mean. A t-test statistically determines if two data sets are significantly different from each other. While a correlation means two variables vary together, it does not prove that one variable causes the other.

1. IB Biology Chapter 0 Notes: Statistics NAME:
Word Definition
Mean A quantity that has a value in between other values; an average. It is one way to
represent the center of the data.
Error bars Bars placed on graphs to show how much the data varies. Error bars can represent
standard deviation or the range of data.
T-Test A test that statistically determines if two data sets are significantly different from
each other.
Standard deviation A measure of how the spread out the data points in a set are from the mean of the
set.
Causation The idea that one thing causes something else.
Correlation The idea that two things vary in a patterned way. As one increases the other
increases (positive correlation), or as one increases the other decreases (negative
correlation).
Range The measure of the spread of a data set. It is the difference between the largest and
smallest values.
Normal distribution When a large sample is taken, the most common data points are values that fall
within the center of the values collected. When a frequency graph is made the graph
has a bell shape.
Probability How likely something is to happen or be true.
Null hypothesis The hypothesis that there is no difference between two sets of data.
Variability A description of how much the data points will be different from each other.
Median The middle number in a sequence of numbers. This is a measure of center.
Mode In a set of numbers the number that is most common within the set. This is a
measure of center.
Frequency How common a data point occurs.
Percent error/change The percent that the experimental value differs from a known value (real value).
Outlier A data point that is very different from the other data points in a set. There are
statistical tests that can be done to determine if a data point is an outlier.
Significance In this chapter it doesn’t mean that it is important but that there has been statistical
tests to show that something is very likely to be true.

2. 0.1.1 State that error bars are
a graphical representation of
the variability of data
0.1.2 Calculate the mean,
range, and standard
deviation of a set of values
0.1.3 What is normal
distribution? What does the
graph look like?
0.1.4 State that the term
standard deviation is used to
summarize the spread of
values around the mean, and
that 68% of values fall
within one standard
deviation of the mean
0.1.5 Explain how the
standard deviation is useful
for comparing the means and
spread of data between two
or more samples
0.1.6 Deduce the
significance of the difference
between two sets of data
using a T-Test
0.1.7 Explain that the
existence of a correlation
does not establish that there
is a causal relationship
between two variables
How do you calculate?
Mean:
Range:
Standard deviation: Use Excel or TI-84 Calculator
Graph:
What is the purpose of performing a T-Test?
What P-value indicates significance to a 95% level of confidence?