7.3.5

Presentation & Display of Data

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Presentation and Display of Quantitative Data

Quantitative (numerical) data tend to be displayed using graphs and charts. The most common examples are tables, bar charts, and (for correlation) scattergrams.

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Tables

  • When writing up the results of their research, psychologists tend to display findings in graphs and tables.
  • A table is a simple way to display numerical findings — usually in the form of descriptive statistics such as the mean and standard deviation.
  • It is often easier for the reader to find information in a table than from a written text.
  • Tables can also be used to summarise qualitative data.
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Charts

  • A chart shows the data in a more visual way. It can be helpful to illustrate smaller and larger differences between conditions.
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Bar chart

  • The bar chart is the most commonly used type of graph in psychology research:
    • The bar chart usually shows the IV along the base (x axis).
    • The DV is shown up the side (y-axis), with the height of the bars indicating the mean score.
    • Each bar represents one condition of the IV.
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Histograms and pie charts

  • Histograms and pie charts are less frequently used.
  • A histogram shows a continuous variable along the horizontal (x) axis, such as the age range of different participants, and line graphs have a similar purpose.
  • A pie chart should represent fractions of a whole. It is not the right choice for showing the DV in a study, but could be used to describe characteristics of a sample.
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Scattergrams

  • Scattergrams are only used to show correlations, not the results of experiments.

Data Distributions

Data are often assumed to be normally distributed, but some sets of data are skewed distributions.

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Normal distribution

  • The normal distribution describes a set of data where scores are very common in the middle of the distribution (close to the mean) and become progressively less common the further they are from the mean.
  • IQ is an example of a normally-distributed variable.
  • On a line graph, a normal distribution appears as a bell-shaped curve.
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Mathematical properties

  • A normal distribution has certain mathematical properties:
    • 50% of scores fall above the mean, and the other 50% below the mean.
    • Approximately 68% of scores fall within one standard deviation above or below the mean.
    • Approximately 95% of scores fall within two standard deviations above or below the mean.
    • Each tail of the graph gets progressively closer to zero, meaning that they become less and less common as they get further from the mean.
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Skewed distribution

  • A skewed distribution is similar to the normal distribution’s bell-shaped curve but the bulk of scores fall more to one side of the median score, with a longer ‘tail’ on the other.
  • A very difficult test or exam may result in a skewed distribution, with many low scores and only a few high scores.
  • Average income is also skewed - most people are at or below the median income, and only a few have very high incomes.
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Positive skew

  • In a positively skewed distribution, the mode is a lower value than the mean and median. The skew is to the right.
    • If the distribution of A level results were positively skewed this would mean that more students were achieving the lower grades than the higher grades and the modal grade might be a D. In this case, the exam board might lower the grade boundaries in order to achieve a more normal distribution of results.
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Negative skew

  • In a negatively skewed distribution, the mode is a higher value than the mean and median. The skew is to the left.
    • If the distribution of A level results were negatively skewed this would mean that more students were achieving the higher grades than the lower grades and the modal grade might be a B. In this case, the exam board might raise the grade boundaries in order to achieve a more normal distribution of results.

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1Social Influence

2Memory

3Attachment

4Psychopathology

5Approaches in Psychology

6Biopsychology

7Research Methods

8Issues & Debates in Psychology (A2 only)

9Option 1: Relationships (A2 only)

10Option 1: Gender (A2 only)

11Option 1: Cognition & Development (A2 only)

12Option 2: Schizophrenia (A2 only)

13Option 2: Eating Behaviour (A2 only)

14Option 2: Stress (A2 only)

15Option 3: Aggression (A2 only)

16Option 3: Forensic Psychology (A2 only)

17Option 3: Addiction (A2 only)

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