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Biometrical exercise 1 - Answers
- Suggest a method of randomly allocating ewes to each group
There are many methods of randomly allocating ewes to the two groups. One suitable one would be to run the ewes through a race, drafting every alternate ewe into one group and the other ewes into a second group. Any method that is random and helps reduce bias and chance, to hopefully gain a more reliable and representative set of results would be acceptable.
- Calculate the mean for each group
Sire Breed A mean = 48.2 Sire Breed B = 52.6.
- Compare the means for the two groups.
Sire Breed A has a mean of 48.2 kg while Sire Breed B has a mean of 52.6 kg.
- Whick group has the better mean for liveweight at 24 weeks
Sire Breed B has a better mean liveweight than Sire Breed A.
- Compare the standard deviations for the two groups.
Sire Breed B has a greater standard deviation than Sire Breed A. This means that the liveweights for Sire Breed B had a larger spread or variation about the mean than the liveweights for Sire Breed A.
- In what way is the standard deviation a useful statistic to know, (what does it tell you about the results?).
The standard deviation is a useful statistic to know because it tells you how far the results are spread about the mean. In many trials it is desirable to have results that have small standard deviation, this means that the results are all closely clustered around the mean, producing a more desirable result.
- List three features of the experimental design that contribute to standardisation of conditions on trial.
Some of the features of this experimental design that contribute to standardisation of conditions include:- all lambs of approximately the same age
- all lambs were from ewes with a similar history
- all ewes were provided with similar nutrition
- all weaners were provided with similar nutrition
- all ram lambs were castrated.
- What is the variable being examined in this trial?
The variable being examined in this trial is the effect of breed of sire.
- What other information would be useful for drawing some conclusions about any differences in carcases from lambs sired by differnet rams?
Other information that would be useful for drawing conclusions about the differences in carcases from lambs sired by different rams, would be:- fat scores
- after slaughter, carcase weight
- after slaughter, eye muscle area measurements.
- What recommendations for other and further trials would you consider useful in examining the effects of different sires on lamb carcases produced?
This trial would need to be replicated many more times over, both with these sires and with other sires of the two breeds involved, to produce results that could be accepted and used with confidence. Information also needs to be provided about how these sires performed within their own breeds.
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