[Air-L] A question for researchers interested in the basics of statistical inference

[Ben Anderson]

Monica,

There are three issues here:

1. the representativeness of your sample with respect to your target  
population (illicit drug users who
used internet message boards)

2. the analysis that you can do with your sample

and

3. What, given 1, you can say from the results of 2 about the target  
population

1. is tricky - you don't have any data (or do you? Does anyone else?)  
on the constitution of the target population. So you can't say how  
biased your sample is. It may not be biased - you may have a  
representative sample along key dimensions for your analysis. But how  
do you tell? This is a problem for all surveys of 'sensitive' issues.  
The usual resolution is to weight your sample so that on key  
dimensions it is representative of the target population. But this can  
only be done if you know the constitution of the target population  
with respect to these dimensions....

2. the analysis. You can certainly do things like regression analysis  
with your sample. The 'statistical significance' simply tells you how  
confident you can be that any statistical effect is real (i.e. non  
random) for the sample.

3. Your problem is that, given 1 you may not be able to make claims  
from the results of 2 about the population - merely what you found in  
your sample. If the sample is biased but you can weight it to account  
for this bias (see 1) then your analysis results for the sample can be  
claimed to be true of the target population.

Others may have different views :-)

Ben

On 3 Sep 2009, at 03:12, Monica Barratt wrote:

> Hi everyone
>
> I'm currently writing up my thesis which has the working title  
> 'Researching
> the forums: Illicit drug use in a networked world'. I conducted an  
> online
> survey using a purposive (nonprobability) sample of illicit drug  
> users who
> used internet message boards (forums) to discuss or read about drugs.
> Originally I intended to conduct inferential statistics on this  
> sample of
> 915, as this is the general practice in many other papers I had  
> read. After
> some more thought though, I'm leaning away from that.

----
Dr Ben Anderson

Sociology @ Essex
http://www.essex.ac.uk/sociology/staff/profile.aspx?ID=118

Centre for Research on Economic Sociology and Innovation
http://cresi.wordpress.com