This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
"Sampling error" occurs due to the variation in results- 
Select and explain. 
A. Between one sample and another, B. Between the observations of two individuals, C. Due to the use of many instruments in the study, D. Due to the multiple readings taken on the same instrument
A: Between one sample and another
Answer: A: Between one sample and another 
Explanation: Taking repeated samples from the same population will result in a difference in the results obtained between samples; this is called SAMPLING ERROR. It occurs because data was gathered between samples rather than from the entire population. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 913