Partition of variation for predicting experimental power with a broiler chicken example

Area of Science:

• Animal Science
• Statistical Methods in Research
• Poultry Production

Background:

• Experimental power, or sampling theory, has been recognized as crucial for determining appropriate sample sizes in poultry research since 1932.
• Despite its recognized importance, experimental power estimates have been infrequently applied in poultry research over the past 90 years.
• Efficient resource allocation and accurate variation estimation in animal experiments necessitate appropriate statistical approaches, such as nested analysis.

Purpose of the Study:

• To analyze bird-to-bird and pen-to-pen variances in poultry research to inform experimental design.
• To evaluate the impact of varying numbers of birds per pen and pens per treatment on statistical power and resource utilization.
• To provide guidance on optimizing sample sizes in poultry studies to balance the detection of differences with the ethical and efficient use of resources.

Main Methods:

• A nested analysis was conducted on two distinct poultry datasets from Australia and North America.
• Bird-to-bird and pen-to-pen variances were separated to understand sources of variation.
• The study simulated the effects of increasing birds per pen and pens per treatment on the standard deviation (SD).

Main Results:

• Increasing birds per pen from 2 to 4 significantly decreased SD, but further increases yielded diminishing returns.
• Similarly, increasing pens per treatment from 2 to 3 reduced SD, with subsequent increases showing a similar pattern of diminishing returns.
• Detecting small differences (1% to 3%) in broiler chicken body weight is challenging due to inherent genetic variability, even with optimized experimental designs.

Conclusions:

• Optimizing the number of birds per pen and pens per treatment is essential for efficient poultry research, balancing statistical power with resource constraints.
• Increasing replication (birds or pens) beyond a certain point provides marginal benefits in reducing variability, highlighting the principle of diminishing returns.
• Effective experimental design in poultry research requires careful consideration of historical data, acceptable risk levels, and the ethical use of animal resources.