anatomy and physiology of clinical research part 4 Flashcards
Learning objectives
At the end of this lecture, you should be able to:
Understand the different types of variables in a clinical study / trial.
Understand the concept of hypothesis testing and sample size effects and how they are applied in a clinical study / trial.
Distinguish between accuracy and precision, and ways to improve accuracy and precision respectively.
Understand how statistical issues are encountered in a clinical study / trial.
Distinguish statistical significance from biological significance.
Appreciate and understand the applications of the abovementioned points to real-world scenarios.
2 types of variables
continuous variable and categorical variable
Continuous variable
quantitative variable which are interval and ratio
Categorical variable
qualitative variable which are nominal, dichotomous and ordinal
Interval (example of continuous variable)
Quantified on infinite scale & have a numerical value.
E.g. temperature scale
Ratio (example of continuous variable)
Interval variables but with added condition that zero of the measurement indicates that there is none of the variable
E.g. Height, weight, distance, number of cigarettes.
What is interval
These are variables which are able to be quantified on an infinite scale and which have a numerical value e.g. temperature, Fahrenheit
The scale can take on both positive and negative values
It is assumed that the intervals keep the same importance throughout the scale
This allows us not only to rank order the items that are measured but also to quantify and compare the magnitudes of differences between them
What is ratio
These are interval variables, but with the added condition that 0 of the measurement indicates that there is none of the variable. Hence temperature is not a ratio variable as 0 does not indicate that there is no temperature.
The name ratio reflects that you can use the ratio of measurements e.g. distance of 10 m is twice the distance of 5 m
Examples of ratio variables include height, weight, distance, number of cigarettes
What is nominal variable
These are variables that have 2 or more categories, but which do not have an intrinsic order
E.g. Blood type for human, there are 4 distinct groups, A, B, AB and O. So blood type is a nominal variable with 4 categories
They tend to have a qualitative and absolute character that makes them very straight forward to measure e.g. 35 people have blood type O
What is dichotomous variable
These are nominal variables which have only TWO categories or levels
E.g. gender, we would most likely categorize someone as “male” or “female”
E.g. “Dead” or “Alive”
E.g. do you own a mobile phone? Or do you have blood type O? the answer would be either a “Yes” or “No”
What is ordinal variable
These are variables that have two or more categories just like nominal variables only that the categories can also be ordered or ranked.
E.g. how often do you consume soya milk? The answer could be “not at all”, “occasionally”, “very frequently”
E.g. how severe is the pain associated with a heart attack? The answer could be “mild”, “moderate” or “severe”
In both examples, you have 3 categories and able to rank them from in the first case, least positive to the most positive and in the second example from the most positive to the least positive
Although we can rank the levels or categories, which gives ordinal variables an advantage over the nominal variables, they do not specify a numerical or uniform difference between one category and the next
Example of ordinal variable : Temperature in DC or F
Zero is an arbitrary point on the scale – it has a value or form of any degree
Zero on the scale does not mean there is no temperature
The difference between -1 and 1 is the same as the difference between 2 and 4 or the difference between 50 – 60 is the same as the difference between 77 – 78
Temperature in Kelvin where zero is an absolute zero – zero is meaningful.
what kind of variable is temperature
continuous variable (interval)
what kind of variable is weight
continuous variable (weight)
what kind of variable is gender
categorical variable (dichotomous)
what kind of variable is stage of cancer
continuous variable (ordinal)
what kind of variable is eye color
continuous variable (nominal)
what kind of variable is blood type
continuous variable (nominal)