psychology statistics

• what is standard deviation?

  a measure of dispersion that shows the spread scores around the mean
• what is variance?


  how far a set of numbers are spread out
• what is an advantage of variance?

  they take every score into account unlike the range
• why is range not always representative?

  • as it only considers the lowest + highest scores
  • doesn't consider the values in between
  • could be skewed by outliers
• what does $\sum_{ }^{ }$ mean?


  the sum of
• what does x̄ mean


  mean
• what is x̄ called?

  x bar
• what is $\sum_{ }^{ }$ called?


  capital sigma
• variance equation:


  $s^2$= $\sum_{ }^{ }$$\frac{\left(x-x̄\right)^2}{n-1}$
• standard deviation equation:


  $s$ = $\sqrt{\frac{\sum_{ }^{ }\left(x-x̄\right)^2}{n-1}}$
• what is dispersion?


  a mathematical way to describe the variation or spread in the score from a data set
• what are the two ways range can be found?

  1. lowest value - highest value
  2. lowest value - highest value + 1
• what does a variance of 0 suggest?

  that all the values are identical
• what do bigger values suggest about variance?

  indicate that there is greater dispersion
• how to calculate the range of ordinal data:

  allocate numerical values to the assigned categories in ranked order
• define categorical data

  discrete values that can be grouped into distinct categories eg. eye colour
• define continuous data


  can take on any value within a data set eg. weight
• when are frequency tables (tally charts) used?

  in content analyses + observations
• when are bar charts used?

  to display data from:

  • frequency tables
  • mean scores
  • totals
• when are histograms used?

  to display interval or ratio data
• when are line graphs used?

  • to show the results from 2 or more conditions @ the same time
  • + as an alternative to histograms
• when are pie charts used?

  when we have percentages
• when are scatter diagrams used?

  with correlations to show the relationship between 2 variables
• what are the 6 graphs + charts needed to be drawn + interpreted?

  • frequency table
  • line graph
  • pie chart
  • bar chart
  • histogram
  • scatter diagram
• what does a wide curve suggest in a normal distribution?

  a bigger standard deviation
• what is the significance level usually set at?

  p<0.05 or 5% or 1/20
• how are the central tendencies presented in a positively skewed distribution?

  mode<median<mean
• how are the central tendencies presented in a negatively skewed distribution?

  mean<median<mode
• what is the symbol for chi-square?

  $x^2$
• criteria for using the chi-square test are:

  • DV = a nominal level of measurement
  • research design = independent measures
  • looking for an association or difference between the IV and DV
• chi square test formula:

  $x^2\ =$$\Sigma\frac{\left(O-E\right)^2}{E}$
• what does the 'O' stand for in the chi-square formula?

  observed frequency
• what does the 'E' stand for in the chi-square test formula?

  expected frequency
• what does it mean when the observed value is greater or equal to

  the critical value?

  the association = significant so null hypothesis = rejected + alternative accepted
• what does it mean when the critical value is greater than the observed value?

  the association = NOT significant so null hypothesis = accepted + alternative = rejected
• how to calculate degrees of freedom:

  • (no. of rows - 1)$\times$(no. of columns - 1)
• strengths of the mode:

  • is less affected by skew
  • can be calculated for all types of data
• weaknesses of the mode:

  • we may get multiple values or none at all
  • less representative unless data contains large skew
• strengths of the median:

  • we always get one value
  • is less affected by the skew
• weaknesses of the median:

  • less representative unless data contains a large skew
  • can only calculate for interval/ratio + ordinal data