Descriptive statistics

• Significant figures: first non-zero digit from left to right
• Estimation: round to 1 significant figure and calculate
• Order of magnitude: how much larger one number is compared to another. 1 magnitude is 10 times
• Measures of dispersion: measure how spread out a set of data is (includes range, variance, and standard deviation)
• Range: difference between highest and lowest value
• Range strengths:

  -easy to calculate
• Range weaknesses:

  -heavily influenced by outliers

  -doesn’t tell you distribution of numbers
• Variance: tells us spread of scores
• A small variance means scores are similar and close to the mean
• A large variance means scores are at a larger distance from the mean
• Standard deviation: average amount a number differs from the mean (is variance square rooted)
• Strengths of variance and standard deviation:

  -a precise measure of dispersion because all the exact values are taken into account

  -not difficult to calculate with a calculator
• Weaknesses of variance and standard deviation:

  -may hide some of the characteristics of the data (eg. outliers)
• Why is standard variation better than variance:

  -standard variation is much more typical of data collected

  -variance is artificially large as numbers are squared
• Ways to show data:

  -frequency table

  -bar chart

  -histogram

  -line graph

  -pie chart
• Frequency table: a table displaying how many times a certain event happens

  -tally marks are used for counting

  -content analysis (qualitative data) and observations
• Bar chart: used to represent the data from frequency tables, mean scores or the totals

  -categorical or nominal data
• Histogram: for continuous data

  -no gaps to represent continuity

  -interval data
• Line graph: continuous data on the x-axis

  -alternative to histograms

  -used to show results from 2+ conditions
• Pie chart: represent data or proportion

  -each slice represents a proportion