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Policy Research 101 Statistical Basics & How to Read Research Reports. Keith Curry Lance Consultant RSL Research Group. Qualitative data Observational notes Interview transcripts Documents, images Video, audio Quantitative data Nominal Ordinal Interval/ratio. Data collection

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policy research 101 statistical basics how to read research reports

Policy Research 101Statistical Basics &How to Read Research Reports

Keith Curry Lance

Consultant

RSL Research Group

types of data data collection
Qualitative data

Observational notes

Interview transcripts

Documents, images

Video, audio

Quantitative data

Nominal

Ordinal

Interval/ratio

Data collection

Available data

Survey

Focus group/key informant interview

Other

Types of Data & Data Collection
quantitative data
Quantitative Data
  • Nominal (different groups)
    • Gender, racial/ethnic groups
    • Administrators, teachers, students
  • Ordinal (more/less groups)
    • Age groups
    • Educational attainment levels
    • Strongly agree to disagree scales
  • Interval/Ratio (zero, equal intervals)
    • Numbers (1-N), percentages
data quality criteria
Data Quality Criteria
  • Currency (i.e., time period covered by data)
  • Timeliness (i.e., how quickly after that time period data are reported)
  • Completeness
  • Validity (i.e., meaningfulness)
  • Reliability (i.e., repeatability)
description vs analysis
Description vs. Analysis
  • Describing what is
  • Analyzing cause and effect
descriptive statistics
Descriptive Statistics
  • Frequencies, percentages
  • Means, medians
  • Quartiles, percentiles
  • Comparisons, rankings
  • Trends
means medians
Mean

Arithmetic average

More sensitive to extreme cases

Better suited to interval/ratio data (i.e., with zero)

Example: population of legal service area

Median

50th percentile (middle value)

Less sensitive to extreme cases

Better suited to ordinal data (i.e., no zero)

With even N of cases, median = mean of middle two

Means & Medians
quartiles percentiles
Quartiles

1st, 25th %ile

2nd, 50th (median)

3rd, 75th %ile

Interquartile range (1st-3rd quartiles—boundaries of middle half)

Example: ALA Salary Survey

Percentiles

In practice, usually deciles

10th, 20th, 30th, etc

Example: old standardized test scores

Quartiles & Percentiles
analytical statistics
Analytical Statistics
  • Cross-tabulation
  • Comparison-of-means
  • Correlation
analytical statistics1
Analytical Statistics
  • Cross-tabulation
    • Two nominal variables
      • Materials format and circ status (circulated in past year)
analytical statistics2
Analytical Statistics
  • Comparison-of-means
    • One nominal, one ordinal or interval
      • % of students using databases for public libraries with and without remote access
analytical statistics3
Analytical Statistics
  • Correlation
    • Two interval level variables
      • HPW of school librarian staffing and test scores
      • School poverty status and test scores
      • Perfect correlation (i.e., any variable with itself) = 1.00
how to read research reports
How to Read Research Reports
  • What is the issue at hand?
  • What type of data is presented?
  • How was data collected?
  • Is data descriptive or analytical?
  • What do I know about its quality?
  • What does it tell me?
  • What do I still not know?
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