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#1




Types of scales and Stats tests?
So, there are 4 types of scales in stats.
a. Nominal (categorical) b. Ordinal c. Interval d. Ratio 1. Can somebody explain me what's the difference between them. I mix up ordinal and interval scales as both of them can have different groups in sequence, or not? Any examples which can clear this out. 2. When to use ttest, chi square, one way ANOVA, matched pairs ttest and repeated measures ANOVA? 
#2




Great questions! I don't know the answer to them all, but here are a couple basic quick tricks that I use (of course it's more complicated but I've found i can answer most biostats questions this way):
1) ttest and ANOVA are basically the same in that they both compare the means. The big difference is that ttest compares 2 means, ANOVA compares the means of of 3 or more groups. 2) If you are not given means, then use a chi square test. This is used to compare categories (eg. number of people who responded yes/no, percentage of people who do xyz etc) Those are the basics. A matched ttest is again just looking at the means between groups, except now you are matching variables. For instance, you want to look at the mean drug dose required to treat people who smoked for a mean number of years vs the mean dose in folks who smoked for a different mean number of years. So in this case drug dose and smoking is matched. 
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drnirajmavani (06022011), excellence (05222014), Gulara (09092011), mle guy (06012011), struggle (06022011) 
#3




Quote:
I would like to add: a matchedpairs ttest is used to test whether there is a significant mean difference between two sets of paired data (correlated data). for example:  pair of twins  where the same people are being measured in beforeandafter comparison  when the group is given two different tests at different times 
The above post was thanked by:  
drnirajmavani (06022011), excellence (05222014), Gulara (09092011), mle guy (06012011), struggle (06022011) 
#4




Are we supposed to know how to use Chi square test?
I didnt get any details in the High yield Biostatistics.. 
#5




No we don't have to use the chi square test or compute any other formula. We just have to know that WHEN we have to use them.

#6




Thanks
Thanks a lot heights and bebix.
Now if any can explain the differences between the scales: nominal, ordinal, interval and ratio. Thanks Last edited by mle guy; 06012011 at 12:37 AM. 
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benzo (06032011) 
#7




Types of Numerical data
Types of Numerical data
As data we consider the result of an experiment. A rough classification is as follows: Nominal data Numbers or text representing unordered categories (e.g., 0=male, 1=female // 0=death, 1=alive // 0=north, 1=south, 2=west, 4=east) Ordinal data Numbers or text representing categories where order counts (e.g., 1=fatal injury, 2=severe injury, 3=moderate injury, etc.) Discrete data: This is numerical data where both ordering and magnitude are important but only whole number values are possible (e.g., Numbers of deaths caused by heart disease (765,156 in 1988) versus suicide (40,368 in 1988). Continuous data Numerical data where any conceivable value is, in theory, attainable (e.g., height, weight, etc.) Hope this help Ref: Principles of Biostatistics. Marcello Pagano 
The above post was thanked by:  
Claus_CU (06022011), drnirajmavani (06022011), hassanahk (06022011), mle guy (06022011), struggle (06022011) 
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BiostatisticsEpidemiology 
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