Lab 8 Songbrid Example: Analysis
There are 9 species of songbirds on WKU's campus (species A-I). students systematically searched for songbirds on the north side and south side (bifurcated by the Avenue of Champions).​ The table displays their count data in each region for each species. 
  • A paired t-test will tell us if the difference is significant and potentially meaningful.
  • We will get into the details of this test in lab, but significance is an important concept we should go over first!
When we complete a statistical test, we are actually testing our null hypothesis. We seek to reject the null (i.e., show that there IS NOT "no difference"). Which conversely supports the idea that there is a significant difference.
  • By convention, we seek to have at least 95% confidence in the assertions we make regarding our data and conclusions.
  • To do this we set what we call an alpha value (typically 0.05) and assert that any "p-value" below that number means we can reject our null hypothesis.
  • What this actually means is that 5% of time we could make an error: 5% of the time we will reject a null hypothesis when we should not (a "type I" error), or 5% of the time we will fail to reject one that we should (a "type II" error).
Each type of statistical test provides a "test statistic" (the t-value in a t-test) its value dictates the accompanying p-value. The higher the t-value, generally the lower the p-value. Therefore, for most tests, if our p-value is < 0.05, we can reject the null hypothesis and claim significant (and potentially relevant/ biologically meaningful) findings. A paired t-test of these data yields: p = 0.8286, t = 0.2237, df = 8
  • With a  p > 0.05, and we cannot reject our null hypothesis. 
  • These data show there is not a significant difference in biodiversity of songbirds on the north vs. south side of campus. ​
  • We would be very, very likely to see these results from chance alone

Extend your knowledge

This is a real citizen science project logging bird sightings across the US! Read more about it HERE)
If you need more help with this concept or if you are just curious to know more!
Written and collated by Natalie Mountjoy & Steve Huskey
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