4.10.6) Representing variation graphically

Key information required for this part of the Classification and Evolution topic for OCR A Level Biology

What is discontinuous variation, what are the characteristics of it and what type of graph is used to represent it (give examples of it)

Qualitative data that is grouped into distinct categories; no intermediate values, not affected by the environment, controlled by a limited number of genes; bar chart (blood type, free/attached earlobe, number of petals in a flower)

What is continuous variation, what are the characteristics of it and what type of graph is used to represent it (give examples of it)

Quantitative data which can't be grouped into distinct categories; has intermediate values, affected by the environment, polygenic (controlled by multiple genes); histogram (height, body mass, length of leaves)

What type of data produces a normal distribution curve and what are the characteristics of a normal distribution curve

Continuous data; mean, mode and median are the same, bell-shaped curve around the mean, 50% of values are less/greater than the mean, 68% of values are within 1 standard deviation of the mean, 95% of values are within 2 standard deviations of the mean, 99.7% of values are within 3 standard deviations of the mean

What is the range and what is standard deviation (what is the issue with these)

A measure of the spread of data (outliers may give a false representation of the spread); a measure of the spread of data either side of the mean (requires lots of data to be accurate)

How do you calculate whether correlation in a data set is coincidence or real

Calculate the mean, then calculate (x-mean)^2 in a table and find the sum of it. Substitute this into the Spearman's rank formula, and compare this to the critical value for p = 0.05. If the value calculated is greater than the critical value then the correlation is real

What is a student t test used for and what are the steps used for using it

Compares the mean values of two sets of data; state the null hypothesis, calculate the values for the equation and substitute all the values into this equation, find degrees of freedom using the formula (n1 + n2) -2 and compare this with the critical value in the table for p = 0.05. If the value calculated is greater than the critical value, the difference in the mean is significant