0
$\begingroup$

enter image description hereI have datasets (one 1997-2001, another 2020, 2021) with means and standard deviations that I need to compare. Two different dats information (mass and total number). It is expected that I compare the two data sets using statistical analyses.

A t-test was suggested. However I am unsure how to go about this when there are no original data on the individuals themselves for 2001 data set (only have full original data for 2021). I was able to do a manual hypothesis testing using the two means and standard deviations. I cannot think of any statistical analyses to represent an appropriate comparison without the original data from the 2001 data set. I really would appreciate any kind of help or recommendations.

$\endgroup$
1
  • 1
    $\begingroup$ t tests depend only on means, SDs and sample sizes; Otherwise you can plot say means and confidence intervals. $\endgroup$
    – Nick Cox
    Sep 26 at 15:43
1
$\begingroup$

To follow on what Nick Cox wrote, your situation is you have two populations (1997-2001 vs 2020-2021) with (probably) different variances, and you want to check whether they have the same mean. That's the situation where you would use Welch's t-test.

You have all the numbers to plug into the first formula on the Wikipedia page for Welch's t- test: https://en.wikipedia.org/wiki/Welch%27s_t-test

The thing to be careful of is that with a t-test you're assuming the means are normally distributed. That's not an issue for the 1997-2001 data since the sample size is quite large. For the 2020-2021 data, you'll want to check for normality by looking at the Q-Q plot and seeing if it looks like a straight line.

$\endgroup$
2
  • 2
    $\begingroup$ (+1) There is an important detail to flag. As not all birds are found to contain plastic, the mean plastic content is a mean over several zeros and several positive weights. That bimodal distribution is going to be a little awkward as underlying the sampling distribution of the mean. You could do simulations on the conditional distribution or use bootstrapping to get a handle on the consequences. $\endgroup$
    – Nick Cox
    Sep 26 at 16:18
  • $\begingroup$ You guys have no idea how thankful I am for your input! Your suggestions helped me big time. Thank you both so much :) $\endgroup$ Sep 27 at 2:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.