3 - Distribution And Graphs

Question 0

What is a frequency polygon?

Answer 0

A graph formed by joining the midpoints of histogram column tops

Question 1

How can frequency distributions be portrayed?

Answer 1

Frequency tables, histograms, polygons

Question 2

How do you calculate
A) Relative frequency
B) percentage frequency

Answer 2

Relative frequency = frequency / no. Observations

Percentage frequency = relative frequency x 100

Question 3

How do you decide on the class interval size?

Answer 3

Units per class interval = range / no. Of class intervals

Range is the highest value - smallest value + 1

Question 4

A) What is the standard deviation?

B) what is standard error? How is it calculated?

Answer 4

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

Question 5

What is variance and how is it calculated?

Answer 5

Variance = measure of the variability of the data

= (S.D.)*squared

Question 6

What is Poisson distribution? Give an example

Answer 6

Probability that n events will occur in an interval (area or time)
E.g. Lightning strikes per hour

Question 7

What is binomial distribution? What effect does it have on variance vs mean and distribution

Answer 7

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

Question 8

What is the binomial population equation?

Answer 8

Psquared + 2pq + qsquared = 1

Question 9

What are the categories used to define / compare normal, binomial, Poisson and negative binomial distribution

Answer 9

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

Question 10

Give some different types of graphs and their uses.

Answer 10

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

Question 11

When is a pie chart inappropriate?

Answer 11

When there are over 6 components or the values of the components are similar.

Question 12

Give some uses of a scatter plot

Answer 12

Data correlation
Positive or negative relationships
Non linear patterns
Spread of data
Outliers

Question 13

What is r? What does the difference between -r and +r?

Answer 13

Correlation coefficient - always between -1 and 1

-r is inverse correlation eg weight over time