Descriptive statistics

• What are the 3 measures of central tendency?

  Mean

  Median

  Mode
• Calculate mean?

  • Average
  • Adding up all data from set and dividing it by the number of numbers
• Mean strength and limitation

  • Most sensitive measure, includes all scores and values within calculation which may be highly representative of data set
  • Easily distorted by extreme values, reduces overall representation of data set and may not reflect results accurately
• Calculate median?

  • Middle value
  • Order scores from lowest to highest
  • Median is halfway between scores
  • If data set is even add two middle scores together and divide by 2
• Strength and limitation of median?

  • Extreme scores do not affect the final value of data recorded, remains the same, may mean that it is more reliable
  • Less sensitive as not all scores are included in calculation, therefore a less representative measure of CT
• Calculate mode?

  • Most frequent/occurring value within a data set
• Strength and limitation of mode?

  • Crude measure, is not representative of the data as a whole and reduces set to one score, hard to derive conclusions from this
  • Easy to calculate
• What are the 2 ways to measure dispersion?

  • The spread of scores, how they vary
  • Range
  • Standard deviation
• Calculate range?

  • Take the highest value and minus the lowest value
  • Then add 1
• Strength and limitation of range

  • Easy to calculate and provides a basic idea of how the data is dispersed, easy to identify variability
  • Only takes into account the two most extreme values, outliers can skew set, therefore unrepresentative of data set and conclusions can't accurately be derived
• What is standard deviation?

  • A single value that tells us how far scores deviate from the calculated mean
  • The larger the value, the greater the dispersion, may suggest not all ppts were affected in the same way as data is widely spread
  • The smaller, the closer together in variability, may suggest ppts responded in a fairly similar way and was more consistent
• Strength and limitation of SD?

  • Includes all values in final calculation, therefore representative of data set given
  • Can be distorted by an anomaly or extreme value, distorting final value and conclusions derived from it