# BASIC STATISTICS WE MOST OFTEN USE Student Affairs Assessment Council Portland State University June 2012.

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BASIC STATISTICS WE MOST OFTEN USE Student Affairs Assessment Council Portland State University June 2012

Overview of the Session Introduction to statistics Things to know before you run statistics How to run & understand descriptive statistics using Campus Labs

How we use statistics in assessment Produce information for decision making & improvement Take data points and transform them into information Descriptive rather than inferential. Need to know if do these: Surveys (focus of today’s examples) Experiments Quasi-experiments Secondary data analysis (e.g., using institutional datasets) Rubrics (the scored part)

Consider these before you run statistics! What does your instrument measure & how well does it do it? (reliability and validity) Who participated and how representative are they? (sampling) What levels are you measuring, as it matters for the types of analyses you can run (ordinal, nominal,…)

What does your instrument measure & how well does it do it? Face and Content Validity How to do: Review by subject-matter expert Link to literature review and/or theoretical framework Align with content of your program. Pilot-test item quality with representative sample

Who participated and how representative are they? (sampling) Population: Entire group that is of interest to you (e.g., all enrolled undergraduate students). Sample: Sub-set of your population (e.g., sample of 1000 undergraduate students). Respondents: are then the number of people who respond to your survey. Match to original population by looking at demographics of your respondents

What levels are you measuring Statistics are appropriate or inappropriate based on the levels of measurement in your data. Levels of measurement Nominal Ordinal Continuous

Nominal Data Categorizes without order = categorical data Applies to data which are only classified by name, labels, or categories (e.g., gender, living on or off campus, political affiliation, yes/no) N, %, Mode

Ordinal Data Assigned order that matters Differences between categories may not be equal (e.g., Strongly agree, Agree, Disagree, Strongly disagree) N, %, mode often treated as continuous 4 3 2 1 -

Continuous Interval & Ratio Categorizes based on difference, order, AND units of equal difference between variables (e.g., individuals’ IQ scores and difference across and between those scores; age, salaries) N, &, Mean, Median if skewed

Two kinds of statistics Descriptive Discuss a large amount of data in an abbreviated fashion Highlight important characteristics of data Inferential Go beyond description Show relationships between groups Use sample data to draw inferences about the population

Descriptive Statistics Measures of Frequency Count, Percent, Frequency Shows how often something occurs or a response is given Measures of central tendency Mean, median, mode Locates the distribution by various points Show average or most commonly indicated response Measures of dispersion or variation Range, variance, standard deviation Identifies the spread of the scores by stating intervals Range = high/low points Variance or Standard Deviation = difference between observed score and mean Measures of position Percentile ranks, quartile ranks Describes how scores fall in relationship to one another Example: Scores that indicate a students’ score falls within the 90th percentile of standardized group Use this when you need to compare scores to a normalized score (usually a national norm)

Measures of Frequency Acceptable for all data levels Count/Frequency – the # who gave response Percent – count/total possible responses. Use when comparing data.

Measures of Central Tendency Ordinal and Continuous data Mean: the average (e.g., 3.25) Median: value of the data that occupies the middle position when the data is ordered from smallest to largest Mode: data point/answer that occurs most frequently

CountPercentageMean Reporting Counts, Percents or Means

Measures of Dispersion: How spread out are the data? Is there a large variation in student answers to how welcomed they feel in the Student Union? Standard deviation: Average distance from the mean. small standard deviation means that scores or values cluster around the mean.

Inferential Statistics Compare groups Generalize from the sample to the population Determine if the difference between groups is dependable or by chance Correlations Chi-square tests T-tests ANOVA Regression

Comparisons in Campus Labs Key-Performance Indicators (KPI): track means or percentages over time StudentVoice Benchmarking T-Test Calculations in their comparative reports https://www.studentvoice.com/app/wiki/Print.aspx?Page= Viewing%20Benchmark%20Project%20Results https://www.studentvoice.com/app/wiki/Print.aspx?Page= Viewing%20Benchmark%20Project%20Results Directions for these under WIKI https://www.studentvoice.com/app/wiki/MainPage.ashx

Example of a comparative analysis report

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