[R] Compute the Gini coefficient

[Achim Zeileis]

On Wed, 30 Mar 2016, Erich Neuwirth wrote:

>
>> On 30 Mar 2016, at 02:53, Marine Regis <marine.regis at hotmail.fr> wrote:
>>
>> Hello,
>>
>> I would like to build a Lorenz curve and calculate a Gini coefficient in order to find how much parasites does the top 20% most infected hosts support.
>>
>> Here is my data set:
>>
>> Number of parasites per host:
>> parasites = c(0,1,2,3,4,5,6,7,8,9,10)
>>
>> Number of hosts associated with each number of parasites given above:
>> hosts = c(18,20,28,19,16,10,3,1,0,0,0)
>>
>> To represent the Lorenz curve:
>> I manually calculated the cumulative percentage of parasites and hosts:
>>
>> cumul_parasites <- cumsum(parasites)/max(cumsum(parasites))
>> cumul_hosts <- cumsum(hosts)/max(cumsum(hosts))
>> plot(cumul_hosts, cumul_parasites, type= "l?)
>
>
> Your values in hosts are frequencies. So you need to calculate
>
> cumul_hosts = cumsum(hosts)/sum(hosts)
> cumul_parasites = cumsum(hosts*parasites)/sum(parasites)

That's what I thought as well but Marine explicitly said that the 'host' 
are _not_ weights. Hence I was confused what this would actually mean.

Using the "ineq" package you can also do
plot(Lc(parasites, hosts))

> The Lorenz curves starts at (0,0), so to draw it, you need to extend these vectors
>
> cumul_hosts = c(0,cumul_hosts)
> cumul_parasites = c(0,cumul_parasites)
>
> plot(cumul_hosts,cum9l_parasites,type=?l?)
>
>
> The Gini coefficient can be calculated as
> library(reldist)
> gini(parasites,hosts)
>
>
> If you want to check, you can ?recreate? the original data (number of parasited for each host) with
>
> num_parasites = rep(parasites,hosts)
>
> and
> gini(num_parasites)
>
> will also give you the Gini coefficient you want.
>
>
>
>>
>
>>> From this Lorenz curve, how can I calculate the Gini coefficient with the function "gini" in R (package reldist) given that the vector "hosts" is not a vector of weights ?
>>
>> Thank you very much for your help.
>> Have a nice day
>> Marine
>>
>>
>> 	[[alternative HTML version deleted]]
>>
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>
>