We can all be above average (almost)

I was reading a very interesting article on behavioural psychology today and its effect with relation to Peak oil, climate change etc. I really liked the article, it does a pretty good job of explaining skepticism towards change, it is a must read for certain. I could not help but notice a common enough error with statistics.
To illustrate a point about human optimism particularly with regards to our own abilities, the author quotes research showing how people think that they are better drivers than average (88%) or that professors think that they are better than average (94%), which is obviously impossible as "By definition, almost half of those surveyed are 'overly optimistic'" or in other words 38% of drivers surveyed and 94% of professors must be wrong. Interestingly, it is possible for the surveyed people to be right, although very unlikely and here is why.

The arithmetic mean or average of a distribution is simply the sum of all values of the distribution divided by the number of items in the distribution. Say that we quantify driver ability on a scale of 0 to 1000, where 1000 is the driving skills of Michael Schummacher coupled with the law abiding ethos of a 50 year old German protestant pastor and 0 is the law abiding ethos of an Italian teenager coupled with the driving skills of a 100 year old arthritic, half blind grandmother.

We take a random selection of 10 people and measure their driving skills. These are their results:

1. 501
2. 500
3. 504
4. 502
5. 503
6. 508
7. 516
8. 490
9. 491
10. 532

The average of the above distribution is 504.7 and thus we have 80% above average. what is going on here, I hear you ask?

Nothing much, just good old fashioned confusion, here is another distribution, this one is the annual salaries of ten friends who have met for a dinner party.

1. £50100
2. £50000
3. £50400
4. £50200
5. £50300
6. £50800
7. £51600
8. £49000
9. £49100
10. £532000

On this distribution 90% are below average, the average is close to £95k.

The author confused arithmetic mean with the median, which is described in Wikipedia as: a median is described as the numeric value separating the higher half of a sample, a population, or a probability distribution, from the lower half.

As I have shown it is possible to have almost everybody above or below average it is impossible to have more than 50% of the drivers above the median, by definition.

This post was just a little bit of facetiousness, his point still stands even if he conveyed it poorly. People think that they are above average and above the median.

Incidentally, the median for the first distribution is: 503 and for the second: £50300.

Add users from other domains to SharePoint

This post should be part of the brain dump series but I never got around to do actually posting it and I sort of needed it last week, at any rate.

A pretty simple command to allow users from other (trusted) domains to be added to SharePoint site:

stsadm -o setproperty -pn peoplepicker-searchadforests -pv "domain:prod.local,prod\ppSP,<password>" -url "https://sp.dev.local"

In our case the problem was that we could not add users from the prod domain, which we use to log in to our machines to the development environment, which we use, well for development :). 

So we created an account in the Prod domain, ppSP, to allow the AD lookups to take place. There needs to be a domain trust between the domains, if there isn't then, you should be looking at claims authentication.

Calculate MD5 or SHA1 Hash Values from PowerShell

I recently had to rebuild my machine due to a hard disk failure, which meant that I've been downloading quite a bit of stuff from MSDN and since I've been doing working with PowerShell quite a bit, I thought I'd better write a couple of functions to check the hashes of stuff I've downloaded.

MD5

function MD5
{
 param ( [string] $inputFile )
 
 if($inputFile) 
 {
  try 
  {
   $md5 = new-object System.Security.Cryptography.MD5CryptoServiceProvider
   $file = [System.IO.File]::ReadAllBytes($inputFile)
   $hash = $md5.ComputeHash($file)
   $hash | %{write-host $_.tostring("x2") -nonewline}; ""
  }
  catch
  {
   Write-Error $($_.Exception.Message)
  }
 }
 else
 {
  Write-Host "Please enter the full path to the file you want to calculate the hash for"
 }
}

MD5 C:\downloads\linux.iso

SHA1

function SHA1
{
 param ( [string] $inputFile )
 
 if($inputFile) 
 {
  try
  {
   $sha1 = new-object System.Security.Cryptography.Sha1Managed
   $file = [System.IO.File]::OpenRead($inputFile)
   $hash = $sha1.ComputeHash($file)
   $hash | %{write-host $_.tostring("x2") -nonewline}; ""
  }
  catch
  {
   Write-Error $($_.Exception.Message)
  }
  finally
  {
   $file.Close() 
  }
 }
 else
 {
  Write-Host "Please enter the full path to the file you want to calculate the sha1 hash for."
 }
}

SHA1 C:\downloads\windows.iso

See man profile for details on how to add these to your profile so that the functions are available every time PowerShell is started.

Delete Entity in Ms Dynamics CRM 2011/2013 using OData endpoint

This is really part of the brain dump series but haven't really had the time until now.

So to delete an account it would be invoked like this

deleteEntity("AccountSet","ef02108a-0098-e311-81c2-d89d6763fc38'")

var deleteEntity = function(EntitySet, Id)
{
 url = Xrm.Page.context.getClientUrl() + "/XRMServices/2011/OrganizationData.svc/";
 url += EntitySet + "(guid'" + Id + "')"

 delete(url).fail(function(){alert("An error ocurred deleting " + Id)})

}

var delete = function(url)
{
 return $.ajax({
 type:"DELETE", 
 url:url,
 beforeSend:function(x){x.setRequestHeader("Accept","application/json")},
 });
}

Also, jquery needs to be loaded if you are using Dynamics CRM 2011