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Rates/ numbers

  • 22-09-2006 5:51pm
    #1
    nettranny
    Closed Accounts Posts: 45 ✭


    Hi, can someone explain to me why(using as little mathematical language please!) there is a difference between using the rate of something versus actual numbers. I have some Birth/Death rate data for a population of birds. I have plotted these against the densities of the birds. However, when I plot the actual numbers being born/dying, i get a different results. Can someone explain this or am i being too abstract ?


Comments

  • #2
    ecksor
    Moderators, Social & Fun Moderators Posts: 10,501 Mod ✭✭✭✭ecksor


    It sounds to me like you're seeing a difference between the number that a function or formula outputs and the number that a derivative of the function or formula outputs, but to be honest I'm not really sure if I'm understanding you. Can you illustrate what you mean with an example?


  • #3
    vallo
    Closed Accounts Posts: 243 ✭✭vallo


    Not sure if it's of any use but .. birth rates and death rates would normally be expressed per 1000 of population. If you had a small population, then the rates might be misleading?


  • #4
    nettranny
    Closed Accounts Posts: 45 ✭nettranny


    ^hmmm. the population is only 54 in total. Would that really make such a difference. Ill be back with some full data


  • #5
    Nietzschean
    Registered Users, Registered Users 2 Posts: 7,314 ✭✭✭Nietzschean


    well the rate of the birds die'n can vary massively from the actual numbers of them dieing.

    E.g.
    Take a healthy bird colony, with lets say 2,000 birds, now lets say in an average year, 200 birds die , and 300 are born.

    Take a failing bird colony, lets say 50 birds, and now lets say 25 of those die per year, and only 5 are born.

    Looking at the plain figures the first colony looks pretty bad, 200 deaths, vs the second with only 25.

    But the rates say that the first colony has a 10% mortality rate, while the second one is 50%. So the inverse is true, here the actual figures are misleading, and the rates show the interesting information(this is the usual case)

    so if both bird colonies data was plot on the same graph, in firstly the actual data, for deaths we'd see the healthy colony far above the dieing one.

    Whereas the rates graph would show the dieing colony far above the healthy one.


    I'm not sure if that helps much?


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