Peach Pack 3 Flashcards
What is the difference between DESCRIPTIVE statistics, and INFERENTIAL statistics?
Descriptive statistics describe the data – they make it easier to understand. They include measures of central tendency, and measures of dispersion.
Inferential statistics explain whether the results are significant or due to chance.
What is the mean?
Sum of values/number of values
interval level
What is the median?
The central value (ordinal level)
What is the mode?
Most frequently occurring value
nominal level data
What are the strengths of the mean?
- Uses all the information in a set of data as operating at the interval level
- Most powerful and sensitive
- Representative of the data
What are the weaknesses of the mean?
- Can be distorted by skewed data
- Not useful for ranked (ordinal) data or nominal level data
- Sometimes does not reflect reality
What is the strength of the median?
Not distorted by skewed data
What is a strength of the mode?
Not influenced by skewed data
What are the disadvantages of the median?
- Less sensitive to the data
- Less meaningful with small sets of data
- Not useful with nominal level data
What are the weaknesses of the mode?
- not sensitive
- Not useful with many modes
What is standard deviation?
How much on average each of the scores in a data set deviates from the mean.
How can you estimate the outcome of a calculation?
Round all of the numbers to 1 significant figure.
Then do the calculation with these numbers
What is the rule for multiplying powers in standard form?
•To multiply powers you add
What is the rule for dividing powers in standard form?
To divide powers you subtract
What are descriptive statistics and why are they used?
Descriptive statistics are used to describe the main trends in the data.
They are used to summarise the raw data from research into a more meaningful form to help researchers draw conclusions from the results.
What is a measure of central tendency?
A measure of central tendency is ‘the value in a group of values which is the most typical’ for the data set.
Identify the 3 measures of central tendency
- Mean
- Mode
- Median
What is a measure of dispersion?
They are a measure of weather the scores are clustered closely around the mean or are scatted widely.
What is the range?
The range is the difference between the largest and smallest scores in the data set.
What are the advantages of the range?
Quick and easy to calculate
What are the limitations of the range?
- Less effective with skewed data
- Very rough estimate of dispersion
What are the advantages of standard deviation?
- Sensitive to the data as every score is used
- Most powerful
- Likely to be representative of the data
- Less effected by skewed data than the range
What are the disadvantages of standard deviation?
-Can take a long time to calculate by hand
Explain how the median is calculated
- Put the values in order from smallest to largest
- Select the middle value
- If there are two middle values, use the mean of the two
When are bar charts used?
What are pie charts used to show?
A pie chart is a way of summarizing a set into data in categories.
Or displaying proportions.
What do scatter diagrams show?
Scatter diagrams are used to show a relationship between two co variables.
The data points are plotted but never joined up.
What is the equation to workout the degree of each proportion in a pie chart?
(No. Out of total/ total) x 360 = degrees of a circle
Describe histograms
The histogram is used to summarise data that are measured on an interval scale.
In a histogram, frequency is shown by the area of the column.
The area of the rectangle represents the proportions of frequency of observations falling into that group.
How do you calculate frequency density for histograms?
Frequency density = frequency ÷ class width
In histograms the data is continuous so there is no gaps in between the bars.
True or False
True
What should the y axis be labelled in a histogram?
Frequency density
Describe normal distribution
Explain positively skewed distributions
When the mode < the median < mean the data is positively skewed.
This means the scores or measures are mainly towards the lower end of the distribution but there is a score that is very high.
The mean is pulled upwards (in a positive direction) towards this high
score.
The median stays in the middle of the distribution because it is not
influenced by the extreme score.
The mode, as the most frequently occurring score, will be at the peak
of the curve.
Explain negatively skewed distributions
When the mean < the median < mode the data is negatively skewed.
This means the scores or measures are mainly towards the higher end of the distribution but there is a score that is
very low.
The mean is pulled downwards (in a negative direction) towards this low score.
The median stays in the middle of the distribution because it is not influenced by the extreme score.
The mode, as the most frequently occurring score, will be at the peak of the curve.
What are the key things to remember when constructing a bar chart?
What are the key things to remember when constructing a scatter diagram?
When should you use a scatter diagram?
