Interpreting Evidence
Learning Objectives
- Use frequency tables and histograms to display and interpret the distribution of a variable.
- Compute and interpret the mean, median, and mode of a distribution and identify situations in which the mean, median, or mode is the most appropriate measure of central tendency.
- Compute and interpret the range and standard deviation of a distribution.
- Describe differences between groups in terms of their means and standard deviations, and in terms of Cohen’s d.
- Describe correlations between quantitative variables in terms of Pearson’s r.
- Write out simple descriptive statistics in American Psychological Association (APA) style.
- Interpret and create simple APA-style figures—including bar graphs, line graphs, and scatterplots.
- Interpret and create simple APA-style tables—including tables of group or condition means and correlation matrices.
| וְרָאִיתִי אָנִי, שֶׁיֵּשׁ יִתְרוֹן לַחָכְמָה מִן-הַסִּכְלוּת–כִּיתְרוֹן הָאוֹר, מִן-הַחֹשֶׁךְ.
הֶחָכָם עֵינָיו בְּרֹאשׁוֹ, וְהַכְּסִיל בַּחֹשֶׁךְ הוֹלֵךְ; וְיָדַעְתִּי גַם-אָנִי, שֶׁמִּקְרֶה אֶחָד יִקְרֶה אֶת-כֻּלָּם. |
Then I saw that wisdom excelleth folly, as far as light excelleth darkness.
The wise man’s eyes are in his head; but the fool walketh in darkness: and I myself perceived also that one event happeneth to them all. |
| – Ecclesiastes 2:13-14 |
In science, unlike most other human endeavours, it doesn’t really matter which University you went to or how many degrees you have in validating any conclusion you might put forward. Evidence is the only criteria for determining whether a conclusion is correct or not. Therefore, we need to consider the basics of data analysis in more detail. We will start with descriptive statistics—a set of techniques for summarizing and displaying the data from a sample. We look first at some of the most common techniques for describing single variables, followed by some of the most common techniques for describing statistical relationships between variables. We then look at how to present descriptive statistics in writing and in the form of tables and graphs that would be appropriate for an American Psychological Association (APA)-style research report.
