ratios

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Cforrester
Posts: 2
Joined: Sun Feb 10, 2008 4:23 pm
Occupation: student
Project Question: I tried to determine height by a person's stride. I have a control #, but know that the higher # of steps in my test, the shorter the person should be. I don't know how to calculate what formula or ratio I should use with the people's steps to try & estimate their height.
Project Due Date: Tuesday, Feb. 12
Project Status: I am finished with my experiment and analyzing the data

ratios

Post by Cforrester »

How dI calculate a ratio to use from a control case for # of steps to determine a person's height? I know the more steps a person takes, the fewer # of inches in height they should(??) should be, don't know how to come up with the calculation to use.
barretttomlinson
Former Expert
Posts: 932
Joined: Wed Oct 03, 2007 12:24 am

Re: ratios

Post by barretttomlinson »

Here are some attempts to estimate stride length from height:

http://walking.about.com/cs/pedometers/ ... terset.htm

http://books.google.com/books?id=wqB5aR ... s#PPA60,M1

http://answers.yahoo.com/question/index ... 745AAb1pSi

Hope this helps,

Good luck on your project!

Barrett Tomlinson
tdaly
Former Expert
Posts: 1415
Joined: Sat Nov 08, 2003 11:27 pm
Occupation: Planetary Scientist
Project Question: N/A
Project Due Date: N/A
Project Status: Not applicable

Re: ratios

Post by tdaly »

Cforrester,

The first thing you need to understand is what a ratio is. A ratio is a relationship between two variables expressed as a quotient. In your case, the variables are how many steps it takes a person to go a certain distance and height. So, to find the ratio between these two variables, you simply divide the number of steps it took a person to go a certain distance by that person's height.
All the best,
Terik
Cforrester
Posts: 2
Joined: Sun Feb 10, 2008 4:23 pm
Occupation: student
Project Question: I tried to determine height by a person's stride. I have a control #, but know that the higher # of steps in my test, the shorter the person should be. I don't know how to calculate what formula or ratio I should use with the people's steps to try & estimate their height.
Project Due Date: Tuesday, Feb. 12
Project Status: I am finished with my experiment and analyzing the data

Re: ratios

Post by Cforrester »

Say I get a ratio for my constant of .11. When I divide the # of steps by the ratio, I get an answer of a taller person (8 steps divided by .11 = 73" or 6 foot 1 ). The relationship needs to be when the # of steps increase, the height decrease, but I can't get that to work out. Can you help?
tdaly
Former Expert
Posts: 1415
Joined: Sat Nov 08, 2003 11:27 pm
Occupation: Planetary Scientist
Project Question: N/A
Project Due Date: N/A
Project Status: Not applicable

Re: ratios

Post by tdaly »

cforrester,

I'm assuming that you recorded each person's height (in feet and inches) and counted how many steps it took them to walk a certain distance. Is this correct? Your ratios will only be valid if each person walked the same distance.

So, let's assume that you had someone who is 5'4" walk 20 feet, and they did so in 7 steps. The first thing we need to do is to convert 5'4" into either all inches or all feet (you really can't do division with a number like 5'4"). I'm going to convert to inches. There are 12 inches in a foot, so we multiply 5X12, which gives 60, and then add 4, giving 64". So, someone who is 5'4" is 64" tall. It looks like you've done this for your data, based on your post.

Now can divide to get the ratio we are interested in. The ratio you use depends on what your independent variable is. If you are trying to predict how tall someone is using how many steps it takes them to walk a certain distance, then you would have a ratio of the form inches/step. But, if you are trying to predict how many steps someone will take based on how tall they are, then you would choose a ratio with the form steps/inch.

So, for our example, lets assume we want to predict how many steps a person will take to walk 20 feet based on how tall they are. Our control showed that it took a person who is 64" tall 7 steps to walk to feet. Our ratio, then, is 7 steps/ 64 inches, which is about 0.1094 steps per inch.

Now that we have the ratio, we can predict how many steps it will take a person to walk 20 feet if we know their height. Let's assume that someone is 6 feet tall. 6 X 12 = 72, so someone who is 6' tall is 72" tall. We can now multiply the person's height, in inches, by our ratio. So we have 0.1094 X 72. This is 7.875. So, a person who is 6' tall would take about 8 steps to go twenty feet.

As you have discovered, the answer you get seems counterintuitive. There are several reasons why this may be. Can you think of any?
All the best,
Terik
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