Sep
21

# Quantative data analysis

Filed Under (Data Analysis, program evaluation) by Molly on 21-09-2012 and tagged ,

Quantitative data analysis is typically what happens to data that are numbers (although qualitative data can be reduced to numbers, I’m talking here about data that starts as numbers.)  Recently, a library colleague sent me an article that was relevant to what evaluators often do–analyze numbers.

This article refers specifically to three metrics that are often overlooked by Extension faculty:  margin of error (MoE), confidence level (CL), and cross-tabulation analysis.   These are three statistics which will help you in your work. The article also does a nice job of listing the eight recommended best practices which I’ve appended here with only some of the explanatory text.

## Complete List of Best Practices for Analyzing Multiple Choice Surveys

1. Inferential statistical tests. To be more certain of the conclusions drawn from survey data, use inferential statistical tests.

2. Confidence Level (CL). Choose your desired confidence level (typically 90%, 95%, or 99%) based upon the purpose of your survey and how confident you need to be of the results. Once chosen, don’t change it unless the purpose of your survey changes. Because the chosen confidence level is part of the formula that determines the margin of error, it’s also important to document the CL in your report or article where you document the margin of error (MoE).

3. Estimate your ideal sample size before you survey. Before you conduct your survey use a sample size calculator specifically designed for surveys to determine how many responses you will need to meet your desired confidence level with your hypothetical (ideal) margin of error (usually 5%).

4. Determine your actual margin of error after you survey. Use a margin of error calculator specifically designed for surveys (you can use the same Raosoft online calculator recommended above).

5. Use your real margin of error to validate your survey conclusions for your larger population.

6. Apply the chi-square test to your crosstab tables to see if there are relationships among the variables that are not likely to have occurred by chance.

7. Reading and reporting chi-square tests of cross-tab tables.

• Use the .05 threshold for your chi-square p-value results in cross-tab table analysis.
• If the chi-square p-value is larger than the threshold value, no relationship between the variables is detected. If the p-value is smaller than the threshold value, there is a statistically valid relationship present, but you need to look more closely to determine what that relationship is. Chi-square tests do not indicate the strength or the cause of the relationship.
• Always report the p-value somewhere close to the conclusion it supports (in parentheses after the conclusion statement, or in a footnote, or in the caption of the table or graph).

8. Document any known sources of bias or error in your sampling methodology and in your survey design in your report, including but not limited to how your survey sample was obtained.

Bottom line:  read the article.

Hightower, C. & Kelly, S. (2012, Spring).  Infer more, describe less: More powerful survey conclusions through easy inferential tests.  Issues in Science and Technology Librarianship. DOI:10.5062/F45H7D64. [Online]. Available at: http://www.istl.org/12-spring/article1.html

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