What do semen analysis, Glen Beck and aerial photography have in common?

September 9, 2010Carole 1 Comment »

Thankfully, Nothing!- most of the time. But I ran across this interesting article about how semen analysis and crowd counting utilized the same principle to estimate a number from a small sample. Glen Beck, socially conservative pundit, held a rally in Washington, DC on the mall recently and the estimates of the number of people in attendance varied widely from around 80,000 to 500,000. At the time, it annoyed me because it seemed like if any kind of scientific method was being applied, certainly there would not be such a large difference in the estimates. Well, actually, the scientific method was employed to get the smaller number but then largely ignored by the media in favor of the bigger number which made for a bigger story, I guess.

Anyway, the scientific approach was to take an aerial photo of the mall at the height of the rally and determine the space that the entire crowd took up. Then a small portion of the crowd was actually counted and this number was multiplied to get to the whole number. For instance, if 800 people were counted in one-hundredth of the space, multiplying by 100 would get you a pretty good approximation of the entire number without counting every single person.

Semen analysis employs the same principle. Cell counting chambers come in two main kinds, Hemocytometers and Makler counting chambers. Hemocytometers were designed for counting and differentiating between different kinds of blood cells and Makler counters were designed specifically for counting sperm. Both can be used to count sperm. The principle employed by each device is similar. Each counter has an area for loading the sperm sample, which when topped by a glass cover slip, encloses the same known amount of fluid each time, similar to keeping the area the crowd occupies exactly the same size each time. The human counter counts a set portion of the enclosed area, which is gridded off and visible under the microscope. The number of sperm obtained from counting a portion of grid area is multiplied by the rest of the grid to generate the final number.

Obtaining a true estimate requires that certain rules be observed.

1.The crowd (or sperm in the sample) must be equally distributed. If the sample is not well mixed, it is possible to get a relatively light or heavy concentration of sperm in your sample grid, which obviously throws off the final result. That is why sperm samples aren’t counted right after ejaculation but allowed to sit at warm temperatures to allow the sample to liquefy and become less clumpy and sticky. Normally, this happens within 30 minutes. The sample is moved up and down in a sterile pipette to make the sample more uniform and well-distributed in the sample. In the case of the crowd, it was crowded into the allowable space so they could see the stage, so the aerial photography showed a dense use of the available space.

2. You must have a way to avoid counting the same sperm (or person) twice. Crowds and sperm both move over the counting grid, so you have to be able to avoid counting the same sperm or person over and over again as they move over the grid. You have to define  the beginning and end of each counting grid. With sperm counting, you typically immobilize the sample first so you don’t have to chase them around the grid. Then,  you typically focus on two edges of each grid and count sperm in the middle of the grid and those laying on only two edges of your grid frame. So if you only count sperm falling on the bottom and right edge of each grid, you don’t count the same edges twice as you move along because the bottom of the previous grid becomes the top of the grid below it.  Crowd movement seemed minimal- no riots anyway.

3. Dilute the sample if the grid is too crowded to get an accurate count. If sperm are so concentrated that you can’t tell where one sperm ends and the next one begins, you can’t get a good count. Samples are often diluted to make counting easier and more accurate. The amount you dilute the sample must also be factored in at the end when you determine the final count, otherwise you have an under estimate. Dilution of  the Glen Beck crowd, on the other hand, would be a political, not scientific issue. In addition, obtaining the most accurate crowd count through the scientific method may not always be consistent with political goals. ;0

© 2010, Carole. All rights reserved.

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