Hi Manish,

Though unusual, this is a good question. I would say that the common logics is ... easiness. It is easy to remember that when looking at a phenomenon, you have to determine the half-something rather than, say, the third quartile of the dataset !!!!

What comes first to my mind is easiness: easy to remember and easy to calculate!

Hope this answer will help, best regards,

Pr Philippe Urban

Dear  Manish

A very important and a trivial question.

To me, from a non-biologist's view would be to answer based on the perchance of  being True or a False. It could be basically from the flip of a toss or a coin (Head/tail).  Moving on to this perchance,  the acceptability ratio would be analogous for experimentation. So what if we have in theory could be 50% perchance applicable in practice!

Now the logical and biologists perspective would be to ask if we can draw a conclusion in bringing the experimentation or theory to a conclusion.  The fortunate thing with biology is bioinformatics has had  a role to play these days where 50% is in fact negated and even we have less cut-offs than we assume. Now the same 50% of such things especially when we deal with the points like half-life, LD coefficient of 50 etc. are concerned, we are trying to measure the effectiveness of these entities.

The common goal answered would be is to ask if we can convert the known unknowns to known knowns.  The 50% problem would be solved then.

Best

Prash 

Hello

"50%" is only the "median" (statistic) of the studied population under a given experimental context.

Best

Christian

50 percent of something is something that we determine by mathematical analysis of a trend, which is very important for the purpose of comparison. To simplify, it helps us understand propensity of something in a typical or two different situations. Good question though, seems easy but one has to dig deep to answer. I only gave a small part of its importance. 

A very easy to understand and interpret  statistical data analysis technique. It is generally used to find the 50% values of lethal conc. or dosage values. For e.g. if we need to know how much amount of drug would be appropriate  and how much would be considered as lethal then this method of finding 50% values is efficient. 

It is a good point to discuss. Toxicological LC or LD 50 values are viewed seriously.  The bio-efficacy of any toxic material /chemical is not expected to administer at the dose to which it can kill 100 due to its associated problems.LC 50 is concentration at which 50% resistant population is affected (killed). This proportion of population will have all ((100%) homogeneous resistant and 50% heterogeneous resistant population. The dose and mortality relation is not linear. Mortality increases exponentially with doses. The toxicity can better be understood by its effect over 50% population. However,LC 95,99,99.9 are also used.

http://www.quora.com/What-is-the-significance-of-50-in-biology/answer/Brian-Stephenson-5?__snids__=1085567131&__nsrc__=1&__filter__=all

thanks all ... interesting yet reasonable  inputs from all of you ....

I believe in many cases it is the cutoff between “likely” and “unlikely.” For example, exposure to a dose above LD50 is more “likely” to cause death than “unlikely” to cause death. This is very useful when there is only one case is under consideration or each case is considered individually. A cutoff value at 50% can help reach the best prediction (or best guess) between “yes” and “no.” In many other cases, it is an indicator of the central location. For example, median is the location of the center when all the values are lined up in descending or ascending order. This is very useful when there is only one indicator of location to use; using the center as the reference is usually more helpful than using another reference.