Probability&Significance

• Define probability?


  A measurement of the likelihood that an even will occur
• How can probability be presented?


  Numercially
• Probability of 0?


  = no chance that it will happen = statistically impossible

  • eg getting to the moon in 1 second
• How can probability of 0 also be represented?


  0%
• 1 = what?


  1 =statistically certain

  = 100%

  eg one day i will die
• 2 experimental hypotheses?


  non-directional and directional
• Is the null hypothesis an experimental hypothesis ?


  No
• What do psychologists ideally want to do?


  Reject null hypothesis and accept their experimental hypothesis
• In Psychology, we can never achieve what?


  Statistical certainty BUT there is a significance level
• What is a significance level?


  This is the point at which a null hypothesis can be accepted or rejected
• Accepted significance level for psychologists to use?


  p<0.05

  p = probability
• What does p<0.05 mean?


  The probability that the results of the experiment are due to chance is less than 5%
• p<0.05 details?


  95% of the time the results you have found DO show a significance or relationship

  • only a 5% likelihood that results due to chance
• Why use the p<0.05 level of significance?


  It avoids a psychologist making a type I or Type II error