3 - Distribution And Graphs Flashcards
What is a frequency polygon?
A graph formed by joining the midpoints of histogram column tops
How can frequency distributions be portrayed?
Frequency tables, histograms, polygons
How do you calculate
A) Relative frequency
B) percentage frequency
Relative frequency = frequency / no. Observations
Percentage frequency = relative frequency x 100
How do you decide on the class interval size?
Units per class interval = range / no. Of class intervals
Range is the highest value - smallest value + 1
A) What is the standard deviation?
B) what is standard error? How is it calculated?
A) amount by which a group of measurements differs from the mean
B) spread of the sample means and how they differ from the true mean
S.E. = S.D / Square root of N
What is variance and how is it calculated?
Variance = measure of the variability of the data
= (S.D.)*squared
What is Poisson distribution? Give an example
Probability that n events will occur in an interval (area or time)
E.g. Lightning strikes per hour
What is binomial distribution? What effect does it have on variance vs mean and distribution
A variable that can only take one of two possible value e.g. Incidence of alleles
Variance is less than the mean and values are regularly distributed
What is the binomial population equation?
Psquared + 2pq + qsquared = 1
What are the categories used to define / compare normal, binomial, Poisson and negative binomial distribution
Where the value counts are from (e.g. Defined sampling units or categories)
Whether the variance is smaller or greater than the mean.
How the values are distributed
Give some different types of graphs and their uses.
Pie chart -description of components
Horizontal bar graph - comparison of items, relationships, time series
Vertical bar graph - same uses as horizontal but also shows frequency distribution
Line graph - time series and freq distribution
Scattetplot - analysis of relationships
When is a pie chart inappropriate?
When there are over 6 components or the values of the components are similar.
Give some uses of a scatter plot
Data correlation Positive or negative relationships Non linear patterns Spread of data Outliers
What is r? What does the difference between -r and +r?
Correlation coefficient - always between -1 and 1
-r is inverse correlation eg weight over time
