+ Reply to Thread
Results 1 to 3 of 3

Thread: Help with correcting spatial bias and sampling effort

  1. #1
    Points: 2,093, Level: 27
    Level completed: 62%, Points required for next Level: 57

    Posts
    2
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Help with correcting spatial bias and sampling effort




    Hi.

    I've recently been carrying out a nationwide survey into tick distribution in the UK. I've collected data by questionnaire from vet practices over the last 8months and am just about to start analysing my data but have come across a rather large problem.

    I realise I have a rather large spatial bias in my data. I wanted to cover the whole of the UK randomly. But I have found that vet practices in towns and cities were far more likely to take part than those in the country who don't have as many staff. Is there a way to correct for this?

    Also, I have a problems with sampling effort. I originally asked all vet practices to fill in five questionnaires a week using randomly picked dogs. This hasn't quite gone to plan, some vet practices have done this, others have sent in 3 one week and 12 the next, others have only sent a questionnaire in when they have found a tick on a dog (I want negative results as well as positive ones as I wanted to create a distribution model). Is there any possible way to correct this?

    My statistical knowledge is quite poor, but any help would be fantastic.

    Thanks,

    Faith

  2. #2
    TS Contributor
    Points: 6,789, Level: 54
    Level completed: 20%, Points required for next Level: 161
    terzi's Avatar
    Location
    Mexico City, Mexico
    Posts
    420
    Thanks
    10
    Thanked 34 Times in 33 Posts

    Some recommendations

    PROBLEM No. 1: Representation

    You should avoid those problems using the sampling weights, which you should have calculated based in the sampling probabilities assigned to each vet. This weights can be thought as a measure of how much individuals are represented by an observation. This one would be the best option.

    If you can't obtain the sampling weights, then you could create some "importance weights" to your data. They are are weights that indicate the "importance" of an observation in some vague sense (For instance, if you think that you only reached half of the country vets, you may give each country vet a weight of 2). This is not a formal procedure, so you must be careful when assigning values to each observation.

    PROBLEM No. 2: Missing or Incomplete Data

    This is a common problem in every survey. Usually, statisticians take a larger sample than required so they can drop the useless or incomplete cases. When that is not possible, the only alternative is an amputation method for missing data. Now, this is a bit hard if you don't have a statistical background knowledge so you may need to get some help for that.

    Good Luck
    Statisticians are engaged in an exhausting but exhilarating struggle with the biggest challenge that philosophy makes to science: how do we translate information into knowledge

  3. #3
    Points: 2,093, Level: 27
    Level completed: 62%, Points required for next Level: 57

    Posts
    2
    Thanks
    0
    Thanked 0 Times in 0 Posts

    Thanks for your help Terzi! I'll look in to your suggestions.

    Faith

+ Reply to Thread

           




Similar Threads

  1. geometric sampling bias
    By tresty in forum Statistics
    Replies: 0
    Last Post: 07-15-2010, 12:08 PM
  2. Correcting for measurement error in logistic regression?
    By CowboyBear in forum Biostatistics
    Replies: 5
    Last Post: 07-08-2010, 07:15 PM
  3. Correcting for Autocorrelation in time-series data
    By thaumaturgy in forum Statistics
    Replies: 2
    Last Post: 07-05-2010, 05:21 AM
  4. handling uneven sampling effort
    By treebat in forum SAS
    Replies: 1
    Last Post: 05-06-2009, 04:24 PM
  5. Replies: 0
    Last Post: 09-30-2005, 09:44 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts






Advertise on Talk Stats