Research Methods

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Probability and Significance

  • Probability is expressed a number between 0 and 1
  • 0 means an event will not happen
  • 1 means that an event will definitely happen
  • P value will always be between 0 and 1
  • Probability = number of particular outcomes / number of possible outcomes
  • A significant result is one where there is a low probability that chance factors were responsible for any observed difference, correlation or association in the variales tested
  • Psychologists have concluded that for most purposes, 5% level of significance will be used
  • p = 0.05
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One tailed (directional) hypothesis:

Predicts the direction in whihc the change will take place when the IV is manipulated

Two tailed (non-directional) hypothesis:

It says that a change will take place when the IV is manipulated but does not indicate in which direction

Null hypothesis:

It predicts that no chance will take place and any change occuring is due to chance

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Levels of Measurement

Nominal data:

Used when categorising something; named categories are established by the researcher and an item is counted when it falls into a particular category

Ordinal data: 

Used when data is ranked so that it is possible to see the order of scores in relation to one another

Interval data:

Gives the rank order of scores but also details the precuse intervals between scores in precise units

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Statistical Tests

Spearman's Rho:

  • Used to test a correlation
  • The data is ordinal, interval or ratio


  • Testing for a difference
  • Independant groups design


  • Testing for a difference
  • Repeated measures design
  • Ordinal data


  • Nominal data
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Type One Error:

  • Rejecting the null hypothesis when we should not
  • P level too lenient
  • Says there is a signififcant result when there is not

Type Two Error:

  • Accepting a null hypothesis when we should
  • P level too stringend
  • Says there is no significant result when there is
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Central Tendencies and Dispersion

Central Tendency:

  • Mean (add up and divide by number of results)
  • Median (put into order and find the middle value)
  • Mode (most popular result)

Measure of Dispersion:

  • Range (difference between highest and lowest result)
  • Standard deviation (the spread of values around the mean)
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