Calculate P-Value: Compare Method1 vs Method2 Results

In summary, you have measured doses from an x-ray tube at various positions using two different methods. You want to determine if there is a significant difference between the results using a p-value test. The points are slightly different, so you have 6 degrees of freedom when looking at the differences. You should also consider whether the data are normally distributed before performing statistical tests.
  • #1
lavster
217
0

Homework Statement



This isn't a homework question but figured this is the best place to ask :)

what I have done is measure doses from an x-ray tube at various positions using two different methods, method1 and method2. I would like to say if they are statistically significant or not by using a p-value test. I have no software except excel... I have so many results to do this analysis on. If you could help me with the first one that would be really appreciated. The points are meant to be (slightly) different so its not just a repetition of the same thing. Ie I've not just repeated it 7 times. Its method 1 and method 2 id like to comparepoint method1 method2 % diff
1 203 ~~ 206.2~~ 1.57
2 202.2~~ 204.6~~ 1.17
3 202.9~~ 203.4~~ 0.27
4 202.4~~ 205.9~~ 1.73
5 202.6~~206.3~~1.86
6 202.3~~ 210.1~~3.83
7 202.4~~ 204.1~~ 0.92

Homework Equations


The Attempt at a Solution



so I am assuming my null hypothesis is they are not different.

But is my degrees of freedom 1 or 6?

Also which one of the p-value tests do I use in this situation? most examples I can find is when its a group A vs group B, where the results from group A and group B are not linked. But in mine it is point 1 is point 1 in both and they should be compared together...

Thanks
 
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  • #2
lavster said:

Homework Statement



This isn't a homework question but figured this is the best place to ask :)

what I have done is measure doses from an x-ray tube at various positions using two different methods, method1 and method2. I would like to say if they are statistically significant or not by using a p-value test. I have no software except excel... I have so many results to do this analysis on. If you could help me with the first one that would be really appreciated. The points are meant to be (slightly) different so its not just a repetition of the same thing. Ie I've not just repeated it 7 times. Its method 1 and method 2 id like to compare


point method1 method2 % diff
1 203 ~~ 206.2~~ 1.57
2 202.2~~ 204.6~~ 1.17
3 202.9~~ 203.4~~ 0.27
4 202.4~~ 205.9~~ 1.73
5 202.6~~206.3~~1.86
6 202.3~~ 210.1~~3.83
7 202.4~~ 204.1~~ 0.92





Homework Equations





The Attempt at a Solution



so I am assuming my null hypothesis is they are not different.

But is my degrees of freedom 1 or 6?

Also which one of the p-value tests do I use in this situation? most examples I can find is when its a group A vs group B, where the results from group A and group B are not linked. But in mine it is point 1 is point 1 in both and they should be compared together...

Thanks

Just look at differences, not percentage differences. Why? Well, percentages are quite nonlinear functions of the data (as they are of the form 100*(x-y)/y or 100*(x-y)/x, which are not linear in x and/or y). If you look at the differences, you will have 6 degrees of freedom, because you have 7 differences.

Another issue that may be cause for worry is whether or not the data are sufficiently close to being normally distributed so as to allow for usable results from standard statistical tests. If the data are far from normal, the test results could be meaningless, and you might need to fall back on non-parametric tests.
 

Related to Calculate P-Value: Compare Method1 vs Method2 Results

1. What is a P-value?

A P-value is a statistical measure that helps determine the strength of evidence against the null hypothesis. It is the probability of obtaining a result at least as extreme as the observed result of a statistical hypothesis test, assuming that the null hypothesis is true.

2. How do you calculate a P-value?

The calculation of a P-value depends on the type of statistical test being performed. In general, it involves comparing the observed data with the expected data under the null hypothesis. This is usually done using a mathematical formula or a statistical software.

3. What is the significance level of a P-value?

The significance level of a P-value is the predetermined threshold used to determine whether the result is statistically significant or not. It is typically set at 0.05 or 5%, meaning that if the P-value is less than 0.05, the result is considered statistically significant.

4. How do you interpret a P-value?

A P-value can be interpreted as the probability of obtaining a result at least as extreme as the observed result, assuming that the null hypothesis is true. A lower P-value indicates stronger evidence against the null hypothesis, while a higher P-value suggests that the observed results are likely due to chance.

5. How do you compare P-values from different statistical tests?

P-values from different statistical tests cannot be directly compared as they are specific to the test being performed. However, if the same statistical test is performed on two different sets of data, the P-values can be compared to determine if there is a significant difference between the two sets of data.

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