Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie
Hi there,
There is an issue with role permissions that is being worked on at the moment.
If you are having trouble with access or permissions on regional forums please post here to get access: https://www.boards.ie/discussion/2058365403/you-do-not-have-permission-for-that#latest

Not sure what statistical test to use

  • 18-01-2012 7:38pm
    #1
    seanknowsall
    Closed Accounts Posts: 65 ✭✭


    I am doing a project on a particular habitat and have two areas that I want to compare. Area A has been grazed by sheep and Area B has been grazed by cattle. The two types of grazing has had a different impact on the populations of wildflowers growing here. I have to represent this using some type of stats table... before grazing commenced I did a survey of the species and recorded 51....all 51 species were common to both areas. The area was then divided and grazing started for a set period of time. A year later I went back and found that Area A (sheep) had only 24 of the original 51 whereas Area B (cattle) had 40. My hypothesis is that cattle grazing is a more wildflower friendly regime on unimproved grasslands. I doing an ecology masters and so far have managed to get away without knowing anything about stats...until now!! Any suggestions gratefully accepted!!


Comments

  • #2
    Coles
    Registered Users, Registered Users 2 Posts: 1,021 ✭✭✭Coles


    While you measured the number of individual species, did you also measure the incidences of each one?


  • #3
    seanknowsall
    Closed Accounts Posts: 65 ✭✭seanknowsall


    Coles wrote: »
    While you measured the number of individual species, did you also measure the incidences of each one?

    Ok the problem is the sites are both 1 hectare in size so I firstly established what was growing there and then randomly quadratted 20 times in each site. For example the species Lady's Bedstraw...it occurred in 12 out of 20 quadrats in Site A and 9 in Site B. 60% and 45% respectively. It would be impossible to accuratley count all the individual Lady's Bedstraw specimens in a hectare.

    After the grazing was complete I quadratted the sites randomly again and found a marked difference as you would expect, but more so in the site eaten by sheep (Site A). Ladys Bedstraw was down to 20% in Site A and 30% in Site B.


  • #4
    El Siglo
    Registered Users, Registered Users 2 Posts: 3,803 ✭✭✭El Siglo


    For what you're doing a simple Chi-squared test might work for what you're trying to show, here's an example on wikipedia. You could also do a scatter plot of your data (no. of plant species in site A, no. in site B on both occasions) then fit a model to it and get an R2 value so you can say something like "grazing by sheep correlates with a reduction in plant species" etc...


  • #5
    seanknowsall
    Closed Accounts Posts: 65 ✭✭seanknowsall


    El Siglo wrote: »
    For what you're doing a simple Chi-squared test might work for what you're trying to show, here's an example on wikipedia. You could also do a scatter plot of your data (no. of plant species in site A, no. in site B on both occasions) then fit a model to it and get an R2 value so you can say something like "grazing by sheep correlates with a reduction in plant species" etc...


    Thanks very much for the help.... will do that!!


Advertisement