Representing variation graphically 10.6 Flashcards
what is discontinuous variation
A characteristic that can only result in certain values is said to be discontinuous variation or discrete variation.
There can be no in-between values.
Variation determined purely by genetic factors falls into this category.
An animals sex Is an example of discontinuous variation
what names of bacteria correspond to what shapes
Spherical (cocci)
rods (bacilli)
spiral (spirilla)
comma (vibrios)
corkscrew (spirochaetes)
what graph is used to illustrate discontinous variation
Normally represented using a bar chart, but a pie chart may also be used
what is continuous variation
A characteristic that can take any value within a range is said to show continuous variation
There is a graduation in values from one extreme to the other of a characteristic.
The height and mass of plants and animals are examples of such characteristics
characteristics that show continuous variation are not controlled by a single gene but a number of genes (polygenes).
They are also often influenced by environmental factors
What graphs is continuous data usually shown on
Data on characteristics that show continuous variation are collected in a frequency table.
These data are then plotted onto a histogram.
Normally a curve is then drawn onto the graph to show the trend.
when continuous variation data is plotted on a graph what shape does art usually take
They usually result in the production of a bell-shaped curve known as a normal distribution curve
what are the characteristics of a normal distribution curve
- the mean, mode and median are the same
- the distribution has a characteristic ‘bell shape’, which is symmetrical about the mean
- 50% of values are less than the mean and 50% are greater than the mean
- most values lie close to the mean value-the number of individuals at the extremes are low
What is the standard deviation
The standard deviation is a measure of how spread out the data is.
The greater the standard deviation is, the greater the spread of the data.
If a characteristic has a high standard deviation what does it tell us
In terms of variation, a characteristic which has a high standard deviation has a large amount of variation
What percentage of values lie within each standard deviation
- up to 3 deviations
What is the formula for standard deviation
what are some statistical tests
- student’s t test
- Spearman’s rank correlation coefficient
- chi squared test
what are student t tests used for
Students t test is used to compare the mean values of 2 sets of data.
To use this test the data collected must be normally distributed and enough data should be collected to calculate a reliable mean.
Different sample sizes may be used
what is the numerical range that the p values can take and what do they mean
p values can be anywhere from 0 to 1
the smaller the p value the stronger the evidence against the null hypothesis
what does p value stand for when talking about t tests
probability value
what are the types of correlation that a spearman’s rank correlation coefficient can produce
- no correlation, no relationship between the data
- positive correlation, as one set of data increases in value, the other set of data also increases in value
- negative correlation, as one set of data increases in value, the other set of data decreases in value
