DESCRIPTIVE STATISTICS

• What is descriptive statistics?

  Summaries or describes the data set
• What is a correlation?

  Explores the relationship between two variables and it can be positive or negative.
• No correlation means no relationship between x and y.
• Correlations are described using a correlation co-efficient, which ranges between -1 (perfect negative)and +1 (perfect positive).
• The closer to +1 or -1, the stronger the correlation.
• However:

  Correlations may be linked by a third variable e.g. correlation between sun burn and ice-cream consumption.

  Can find apparent correlation between variables that are not related; not even by a co-variable.
• What is the mean?

  The statistical average.

  • It can be calculated by adding up all the scores in a set of data and then dividing by the number of scores
• What is a benefit of using the mean?

  • Is the most sensitive measure of central tendency, taking all scores into consideration
• What is a drawback of using the mean?

  • Can be distorted by extreme scores with the consequence that it becomes unrepresentative of the data.
• What is the median?

  The middle score after the data is organised according to size.

  • The median is calculated by first putting the data in order and then finding the middle score. If there is an even number of scores you should add the two in the middle and then divide by two
• What is a strength of the median?

  It's unaffected by extreme scores, thus when extreme scores exist this would be a more appropriate measure of central tendency than the mean
• What is a weakness of the median?

  Only takes one or two scores into account—the middle value(s).
• What is the mode?

  The most frequently occurring score/value.

  • It can be calculated by a frequency count— analyse your data and see which score occurs the most.– the most frequently occurring number in a data set.
• What is a strength of the mode?

  The mode is unaffected by extreme scores/outliers.
• What is a weakness of the mode?

  Can be effected dramatically by the change in one score, making it an unrepresentative measure
• What is the range?

  The difference between the highest and the lowest score.

  • Is calculated by subtracting the lowest score from the highest score
• What is a strength of the range?

  Easy to calculate.
• What is a weakness of the range?

  Can be easily distorted by extreme scores.
• What is standard deviation?

  Measures how widely spread the values in a data set are around the mean. The SD allows us to see the consistency with which the IV impacted on the DV.
• What does a large SD show?

  Tells us that there was much variation around the mean.
• What does a small SD show?

   Tells us that the data was closely clustered around the mean.
• What is a bar chart?

  Used to show discrete data (information that can be categorised into a classification, and is based on counts. Only a finite number of

  values is possible, and the values cannot be subdivided meaningfully.)
• What is a histogram?

  A graphical method for displaying distribution shape; used to show continuous data (data that can take any value (within a range)) Example: people's heights. Should be no space between the bars, because the data is continuous. It is particularly useful when there are a large number of observations.
• What is a scattergram?

  Gives a good visual picture of the relationship between the two

  variables and aids the interpretation of the correlation coefficient. Each piece of data contributes to one point on the scattergram, on which points are plotted but not joined. The pattern indicates the type and strength of the relationship.
• What is normal distribution?

  When the mean, median and mode are all close together.
• What are negative distributions?

  Occur when the mode and median are higher than the mean- this

  could be because the task was too easy.
• What are positive distributions?

  Occur when the mean is higher than the mode or median.