Lecture 5- Frequency Distributions

Question 1

What is descriptive statistics?

Answer 1

A collection of methods for classifying and summarizing data

All about description

Question 2

What are the two main types of descriptive statistics?

Answer 2

• Measures of central tendency

- Measures of variability

Question 3

What are frequency distributions? What are the useful for?

Answer 3

The count of the number of occurrences of each different value in the data set
They allow us to organise data and display it for easy interpretation

Question 4

How do you make a frequency distribution?

Answer 4

1. Count the number of occurrences (frequency) of each value of the DV
2. Make a graph with the X axis as the values of the DV and the Y axis the frequency

Question 5

Where is a frequency distribution most useful?

Answer 5

When you have a narrow range of values otherwise there is too much going on in the plot/ graph (causes confusion)

Question 6

What do you do to overcome having a wide range of values when forming a frequency distribution?

Answer 6

Group the data into clusters that form a class interval

Question 7

What are some tips for selecting a class interval width?

Answer 7

• Choose a width so that 10-20 intervals will encompass the range of values you wish to include/ express
• If possible choose an interval width that is odd as this will allow the midpoint of the interval to be a whole number

Question 8

What does having a continuous variable mean in terms of a frequency distribution?

Answer 8

Any value can be taken on the measurement scale (doesn’t have to be a whole number)

Question 9

What are exact limits? e.g. what is the exact limit of the class interval 60-64

Answer 9

1/2 unit below and 1/2 unit above the values of the class interval 
exact limit= 59.5- 64.5

Question 10

How do you calculate the midpoint of a class interval using exact limits? Do this with the class interval 60-64

Answer 10

Lower class limit + 1/2 class interval width= midpoint
mid point= 59.9+2.5= 62

Question 11

What are two types of data curves commonly used to display frequency distributions?

Answer 11

1) Frequency polygon

2) Histogram

Question 12

How do you plot a frequency polygon?

Answer 12

• y axis= frequency, x axis=mark of axis with values corresponding to the midpoints of the class intervals
• To plot place a point above the midpoint of each class interval corresponding to the frequency within that interval. Join the points

Question 13

How do you set up a histogram to display the frequency distribution?

Answer 13

• y axis= frequency, x axis=mark of axis with values corresponding to the midpoints of the class intervals
• To plot create a bar with a midpoint which is above the midpoint value on the x-axis. Height of the bar corresponds to the frequency of that interval.

Question 14

How does a histogram differ between discrete and continuous data?

Answer 14

• No space between bars for continuous data.

- Space between bars for discrete data

Question 15

What 3 possible shapes are there for frequency distributions?

Answer 15

• Uniform or rectangular. Data is evenly distributed so all bars are the same height (rare)
• Skewed distribution. Lots of values at one end and not a lot at the other end.
• Symmetrical distribution. Two halves of the graph are the same.

Question 16

What are the two types of skewed distributions?

Answer 16

• Positively skewed (most data is near the start- hill first)
• Negatively skewed (most data is near the end- hill last)

Question 17

What is the most famous type of symmetrical distribution? Why is this?

Answer 17

• Normal distribution: many scores/ data points in the middle with relatively little at either extremes.
• In science this is extremely common because the universe is ordered

Question 18

What time of distribution is very rare?

Answer 18

Uniform distribution