representing variation graphically

what is discontinuous variation

when a characteristic only results in certain values

what type of variation falls into the category of discontinuous variation

genetic variation- variation that is determined by genetic factors

give 2 examples of characteristics that shows discontinuous variation

1. an animal’s sex → only 2 possible functional values → male and female

2. human blood groups

how is discontinuous variation normally represented

using a bar chart

( a pie chart can also be used)

what is continuous variation

a characteristic that can take any value within a range

what is different about characteristics that show continuous variation compared to discontinuous

• the characteristics that show continuous variation aren’t controlled by a single gene but many genes (polygenes)

• they are also often influenced by environmental factors

how is data that shows continuous variation collected

• it is collected in a frequency table

• is then plotted on a histogram

• and a curve is drawn into the graph to show a trend

what is a normal distribution curve

when the continuous variation data that is plotted on the graphs produces a bell-shaped curve

how is the data distributed on a normal distribution curve

it is distributed normally

what are the characteristics of normal distribution

• mean, mode and median are the same

• distribution has a ‘bell-shape’ that is symmetrical about the mean

• 50% of values are less than the mean

• 50% of values are greater than the mean

• most values lie close to the mean value - number of individuals at the extremes are low

what is standard deviation

the measure of how spread out the data is

if the standard deviation is greater what does it mean

it means that the spread of the data is greater

what does a characteristic that has a high standard deviation mean in terms of variation

that is has a large amount of variation

what are other examples of statistical test

• unpaired student t-test

• spearman rho correlation coefficient

when is unpaired student t-test used

usd to compare means of 2 populations (or 2 means of a set of data)

when is the spearman rho correlation coefficient used

to consider the relationship between two sets of data

what are the conditions of the student t-test

• the data that is collected have to be normally distributed

• there should be enough data collected to calculate a reliable mean

what does it mean if 2 sets of data show no correlation

it means that there is no relationship between the data

what does it mean if 2 sets of data show a positive correlation

it means that as one set of data increases in value, the other set of data also increases in value

what does it mean if 2 sets of data show a negative correlation

it means that as one set of data increases in value, the other set of data decreases in value