Small Sample Size - Test for Difference between Brands with Normal Distribution

In summary, if you have data from two brands of a particular food and want to see if there is a difference in the amount of flour in the food, you would do a two-way analysis-of-variance test.
  • #1
HeapofAsh
6
0
Lets say I have 8 samples (weight) of 4 ingredients in particular food by X brand and another 8 samples by Y brand. I would like to test to see if there is any difference between the two brands in terms of weight of particular ingredients. However, I am not sure what statistic test to run and I don't know whether my data is normal or not (especially because my sample size is small). Any guidance will be helpful.

Thnx
 
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  • #2
HeapofAsh said:
Lets say I have 8 samples (weight) of 4 ingredients in particular food by X brand and another 8 samples by Y brand. I would like to test to see if there is any difference between the two brands in terms of weight of particular ingredients. However, I am not sure what statistic test to run and I don't know whether my data is normal or not (especially because my sample size is small). Any guidance will be helpful.

Thnx

If you are able to assume that the data are at least approximately normally distributed, this would be a two-way analysis-of-variance problem (ANOVA), where you have two brands (X and Y) along one "axis" and ingredient type (1,2,3,4) along the other "axis". WARNING: this is an example of a so-called "nested" two-way ANOVA, because we do not 'cross' ingredient with brand (which would give 4x2 = 8 combinations repeated 8 times---for a total of 8x8 = 64 data points), but rather, just 16 data points. To see what type of tests to perform, look up 'Nested ANOVA'.

You should be aware that some of this type of material is often only covered in a second course in Applied Statistics, and that students have trouble grasping some of it---not to mention getting terminally confused and making lots of errors. Looking at a book (rather than a web page) is preferable, but it should probably not be an introductory textbook.

Anyway, for what it is worth, see, eg.,
http://www.stat.purdue.edu/~zhanghao/STAT514/handout/nested.pdf
http://www.itl.nist.gov/div898/handbook/ppc/section2/ppc233.htm
http://biol09.biol.umontreal.ca/PLcourses/Nested_and_two-way_anova.pdf
http://www3.imperial.ac.uk/pls/portallive/docs/1/1171923.PDF

Other issues arise if the data are not normally distributed (or at least, approximately so), and I know little to nothing about how to proceed in that case. Look up 'non-parametric methods'.
 
  • #3
Ray Vickson said:
You should be aware that some of this type of material is often only covered in a second course in Applied Statistics, and that students have trouble grasping some of it---not to mention getting terminally confused and making lots of errors. Looking at a book (rather than a web page) is preferable, but it should probably not be an introductory textbook.

Yeah it seems beyond my stat course level. How about doing hypothesis test on difference of means or proportion of each type of ingredient.

For the amount (weight) of flour in food by Brand x and Brand y:
H0:Px= Py
HA:Px≠ Py

And do the same for different ingredients. If they it turns out that the Px= Py for all 4 different ingredients, would i be able to say there are no significant difference between the two brands (at least in terms of amount of ingredients).
 

Related to Small Sample Size - Test for Difference between Brands with Normal Distribution

1. What is a small sample size in the context of testing for difference between brands with normal distribution?

A small sample size refers to a dataset that is too small to accurately represent the entire population. In the context of testing for difference between brands with normal distribution, a small sample size can lead to unreliable results as it may not capture the true variability of the population.

2. How does a small sample size affect the accuracy of the test for difference between brands?

A small sample size can greatly affect the accuracy of the test for difference between brands. With a small sample size, there is a higher chance of sampling error, which can lead to incorrect conclusions about the difference between brands. Additionally, a small sample size may not be representative of the entire population, leading to biased results.

3. Is a small sample size always a disadvantage in testing for difference between brands with normal distribution?

Not necessarily. While a small sample size can lead to less accurate results, it may also be appropriate for certain situations. For example, if the population is small or if the difference between brands is expected to be large, a small sample size may still be able to provide meaningful insights.

4. What are some methods to address the issue of small sample size in testing for difference between brands with normal distribution?

There are several methods that can be used to address the issue of small sample size. One approach is to increase the sample size by collecting more data. Another approach is to use statistical techniques such as bootstrapping or Bayesian analysis to account for the small sample size. Additionally, researchers can also consider combining data from multiple studies or conducting a meta-analysis to increase the sample size.

5. Can a small sample size ever be preferable in testing for difference between brands with normal distribution?

Yes, there may be cases where a small sample size is preferable. For example, if the cost or time required to collect a larger sample is prohibitive, a small sample size may be the only feasible option. Additionally, in some cases, a smaller sample size may be more representative of the target population, whereas a larger sample may include individuals who do not accurately reflect the population of interest.

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