Questions for Callaway

[Tesla]

I can't figure this out...  The pregnancy tests are 99% accurate, we have taken the test five times... what is the probability that we have received a false result five times?

My intuition is that every time you take the test, you have a 1% chance of receiving a false result... regardless of how many times you take the test.  Just like tossing the dice.  The previous toss has no bearing on the current toss.  But, I can't reconcile that in my brain.

I haven't taken any classes in this type of thing.

No real pressure, it's just a question that's been bugging me.  I can't figure it out, and that frustrates the hell out of me.

If they were independent events, then the chance of getting five false positives would be (0.01)*(0.01)*(0.01)*(0.01)*(0.01) or something like a billion to one odds.

About the only way you would get five false positives is if Amy were taking HCG because of fertility treatments or something.

I doubt that you could have bought five outdated tests, and I think false negatives would be more likely in that case than false positives.

I have used a lot of home pregnancy tests and the current ones on the market are pretty accurate if you buy a reliable brand and use them as directed. 

Amy still will need to see a doctor, who will probably repeat the test and do some others as well, to figure out how far along she is and to start prenatal care, including prenatal vitamins.

When did her last period start?

She is going to call a doctor tomorrow to schedule an appointment.  We went and bought a bottle of supplements today... based on the recommendations of the book we got today.  Folic acid mainly.

She had very irregular periods which is why her being late wasn't really an issue.  But, her last period started in the last week of April.  Which puts her due date at the very beginning of January 2009.

[Callaway]

I'm sorry, Tesla, I was mistaken in what I said before.

You can get a false positive from using a test that has passed its expiration date.

I only ever got them from taking HCG shots as part of infertility treatment when I tested too soon, though.

False positives

False positive test results may occur for several reasons. These include: errors of test application, use of drugs containing the assay molecule, and non-pregnant production of the assay molecule.

Spurious evaporation lines may appear on many home pregnancy tests if read after the suggested 3–5 minute window or reaction time, independent of an actual pregnancy. False positives may also appear on tests used past their expiration date.

A woman who has been given an hCG injection as part of infertility treatment will test positive on pregnancy tests that assay hCG, regardless of her actual pregnancy status. However, some infertility drugs (e.g., clomid) do not contain the hCG hormone.[13]

Some diseases of the liver, cancers, and other medical conditions may produce elevated hCG and thus cause a false positive pregnancy test. These include choriocarcinoma and other germ cell tumors, IgA deficiencies, heterophile antibodies, enterocystoplasties, gestational trophoblastic diseases (GTD), and gestational trophoblastic neoplasms (GTN). (See Human chorionic gonadotropin.)

[Tesla]

I see. Well, we bought five different tests from three different manufacturers.

I'm pretty sure of the results.

It was mainly just the math I was interested in. 

Thank you for all your thought though.

 

[El]

Question for Callaway:  Do you know of a site that has an GAQ or instructions on how to sort of slipcover a couh using bedsheets?  I guess slipcovers are damn expensive but walmart sheets would prolly be affordable- and prolly worth it, too.  My couches are both hand-me-downs and were grungy as hell before I even got them.   

This would be for the option for less sewing:

http://www.inoutdecor.com/Slipcovers/SofaSlipcover.htm

You could make it like this if you want it to be more custom fitted:

http://www.inoutdecor.com/Slipcovers/ChairProject.htm

that's awesome- thanks Callaway! 

[odeon]

Haven't plussed you in a while, Callaway.

[renaeden]

Callaway, do you normally type with all fingers (am asking in light of recent events and hoping you get good news from the orthopaedic surgeon).

Firefox doesn't like the word "orthopaedic".

[Callaway]

I normally type like I learned to in typing class, with both my hands and all my fingers, but I have never been fast.

Thanks for the good wishes.  I just Googled "broken finger" and I'm a little nervous.

[ANTON_UBER_ALLES]

Okay, here's another one (take your time):
When making homemade yogurt, why do you have to heat the milk to just below boiling, then cool it down to lukewarm (100 to 110 degrees)?  This makes no sense to me since the milk we all use is already pasteurized.

Milk is pasteurized to reduce the bacterial content to 0.00001 of the number of bacteria in unpasteurized milk.  If you wanted to make yogurt from raw milk, you would need to pasteurize it first by heating it to 161.5 degrees Fahrenheit and holding it at this temperature for at least 15 seconds.  Heating the milk to just below boiling changes the structure of the milk protein so that that it does not coagulate and make curds and whey instead of yogurt.  You have to cool it off to lukewarm before you inoculate it with the yogurt culture so you won't kill the bacteria.

Sorry, but the molecular diffusion question is difficult for me to get a good answer for.  Molecular diffusion of the chlorine bleach into still water in the water tank would happen very slowly and that is why stirring it is recommended.  Actually, if the water tank is subject to temperature fluctuations between day and night, you would get convection currents from the colder and warmer water and also if you use water from the tank and add water to the tank periodically, that would mix the water more quickly than molecular diffusion.  I don't know how to calculate these effects in closed form, and a computer model would require a lot more information. 

McJagger, I have a Master's degree in Chemical Engineering.

My first inclination is to suggest actually doing this experiment with radiolabled bleach.

[Tesla]

Question:  I recently bought a Pur 3-stage water filter for our faucet.  It says it removes Chlorine (taste and odor)...  I can't figure out why it says the "(taste and odor)" part.  Does it just remove the taste and odor of chlorine, and not actually chlorine??

[Callaway]

Question:  I recently bought a Pur 3-stage water filter for our faucet.  It says it removes Chlorine (taste and odor)...  I can't figure out why it says the "(taste and odor)" part.  Does it just remove the taste and odor of chlorine, and not actually chlorine??

I just looked on their website and read the same thing.

http://www.purwaterfilters.com/info_pur_vert_fm.htm

I would think that their filter reduces the amount of chlorine in your water and reduces or removes the trihalomethanes which are a by-product of the chlorination of water.  They both would contribute to taste and odor.  For them to be able to say that their filter completely removes the chlorine could depend on how much chlorine there is in the unfiltered water.

I looked up your water quality report:

http://www.ci.apex.nc.us/docs/pw/WaterCCR.pdf

The chlorine levels are within EPA guidelines, 3.12 ppm, but this level would be greatly reduced by an activated carbon filter, which Pur has as Stage 2 of the three stages.

Here is an article discussing activated carbon filters and what they do and do not reduce or remove:

http://www.ag.ndsu.edu/pubs/h2oqual/watsys/ae1029w.htm

Just make sure you change the filter when you are supposed to, or it could become less effective.

[renaeden]

I have a Master's degree in Chemical Engineering.

I think that is so cool. 

When I did Chemistry in school, I would get a funny feeling in my head.....like pressure building up.

[Coral]

When I did chemistry in school, I got a funny feeling in my head too... a migraine!!! It's the only course that actually scared the crap out of me. I thought it would be my first F but I got a C+. Chemistry = 

[Coral]

I have a question for Callaway: My baby died yesterday, and of course I am still grieving, but how long should I wait before adopting a new cat? I have lots of love to give to a fluffy friend and so does my son. I was thinking that having a new cat to love might fill the empty hole that is in my heart. It might distract me from all the crying. I was thinking about adopting a young cat that has been abandoned so that we can turn my tragedy and his into some love.

[Tesla]

You're the best Callaway.  Thank you. 

[Callaway]

I have a question for Callaway: My baby died yesterday, and of course I am still grieving, but how long should I wait before adopting a new cat? I have lots of love to give to a fluffy friend and so does my son. I was thinking that having a new cat to love might fill the empty hole that is in my heart. It might distract me from all the crying. I was thinking about adopting a young cat that has been abandoned so that we can turn my tragedy and his into some love.

While I understand that the temptation after the death of a pet may be to run out and get another one right away and that people are often encouraged to do so by family and friends, and although it may sound like a good idea, I think that you should be careful about getting one too soon.  I think that you need to take some time to grieve first.

As you said, you lost a baby, a member of the family, and you need to come to terms with that loss before adopting a new member of the family.

How would you advise me if I just lost a baby?  I think that you would advise me to come to terms with my devastating loss before having or adopting another baby, wouldn't you?

This new cat deserves to be loved for himself or herself, not just as a replacement cat for the one that is gone.  He or she will need lots of energy and attention, which at some point you will be ready and able to give, but not now.  Your heart needs to heal first.

I think that you need to be especially careful about replacing the cat too soon because of your son.  You don't want to send a message to a child that says when something is lost all you have to do is buy another one, when in reality, that is often not the case.  It also devalues the significance of the cat who just died.

I don't think that there is a specific amount of time that needs to pass, but I think you will know when you and your son are both ready.  If there is any doubt at all, then wait a little longer.