Epidemiology/Introduction - Precision: Page 3 of 3

EPI8-3: Sources Of Variability How Can Precision Be Improved?

SOURCES OF VARIABILITY - HOW CAN PRECISION BE IMPROVED?

Table 2 below summarises the main sources of random variations:

**TABLE 2: SOURCES OF RANDOM VARIATION**
Observer	Intra-observer variation
Observer	Inter-observer variation
Instrument	Questionnaire or other instrument
Instrument	Machine
Respondent	Information recall
	Timing of information recalled
	Emotional state
	Study setting

HOW CAN PRECISION BE ENHANCED?

Remember that the most important methods involve the maximising of the number of observations or measurements, and the training of the observers to high standards.

**TABLE 3: REDUCING THE SOURCES OF RANDOM VARIATION**
Observer	Intra-observer variation	Test reliability in pilot study
Observer	Inter-observer variation	Use a single observer Training of observers and checks Can do repeated measures and use mean Apply clear operational definitions of variables Apply clear description of methods Use standard procedures Use blind methods
Instrument	Questionnaire or other instrument	Use instruments which give consistent measures (have been pretested and validated) Calibrate and check equipment from time to time
Instrument	Machine
Respondent	Information recall	Measure your subjects in similar settings if possible Be aware of subjects' emotional state Make sure your subjects are as comparable as possible
	Timing of information recalled
	Emotional state
	Study setting

General Introduction to Occupational Health: Occupational Hygiene, Epidemiology & Biostatistics by Prof Jonny Myers is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License.