Week 9 - Descriptive Statistics Flashcards
Uses for descriptive statistics
- Descriptive Studies
Descriptive studies- what do they do in a set of data
characterize shape, central tendency and variability within a set of data
what is the purpose of descriptive studies
describe a sample or population
population measures in a descriptive study
parameters
Sample measures in a descriptive study
statistic
- statistics are used to estimate population parameters
Distribution of data
- readiness for statistical testing
what do you need to know for distribution of data
- central point around which data tends to cluster (average)
- measure of central tendency
- “typical value in the set of observations - how far from central point all data lies
- variability - examine visual display of scores
Frequency of distribution
distribution
- total set of scores for a variable
- N=total # of scores in distribution
- summarize data with frequency of distribution; a table of rank ordered scores and frequency of each
How can you graph frequency of distribution
- histogram
- line plot
- stem and leaf plot
- distribution shape: skewed right/positively skewed or skewed left/negatively skewed
Central tendency: mean
- arithmetic average
- can be influenced by extreme values
- sample mean: x̄
- population mean:μ
Central tendency: median
- middle score of distribution
1. put data points in order select middle data point
Central Tendency mode
- score that occurs most frequently in distribution
- blue
- most for categories
Measure of variability
- Range: difference between highest and lowest values of distribution
- percentiles: describe scores position within distribution
- convert scores into comparative scores - quartiles: divide distribution into 4 quarters
Box and whisker plots
- box: interquartile range (between 1st and 3rd quartile)
- whiskers: range of scores
- horizontal line: 50th percentile = median
Coefficient of variation
- ratio of standard deviation to mean
- expressed as %
- can compare between different types of measures, between different distribution