A factor is fixed when the levels under study are the only levels of interest. A factor is random when the levels under study are a random sample from a larger population and the goal of the study is to make a statement regarding the larger population.
A factor is fixed when the levels under study are the only levels of interest. A factor is random when the Variable or fixed factors under study are a random sample from a larger population and the goal of the study is to make a statement regarding the larger population.
The purpose of this study is to examine these three methods of measuring blood pressure. There may be other methods, but they do not concern us here.
When we are done, the hope is to make a statement comparing these three methods. This might be the case where the study concerns the staff of a particular research unit and there is no goal of generalizing beyond the unit.
However, it might be that the point of the study is to generalize the results to all nurses. In that case, these four nurses might be viewed as a random sample of the population of all nurses, making NURSE a random factor. One way to decide whether a factor is fixed or random is to ask what would happen if the study were repeated.
If the same set of nurses would be used as in the case of studying a particular research unit the factor is fixed.
If any set of nurses would do equally well, the factor is random. The F-ratio is 4. When it is compared to the percentiles of the F distribution with 2 numerator degrees of freedom and 24 denominator degrees of freedom, the resulting P value is 0.
Most statistical program packages produce this analysis by default. This F-ratio is 3. When it is compared to the percentiles of the F distribution with 2 numerator degrees of freedom and 6 denominator degrees of freedom, the resulting P value is 0. When factors are fixed, the measure of underlying variability is the within cell standard deviation.
Differences between methods are compared to the within cell standard deviation.
When NURSES is random, methods are evaluated by seeing how much they differ on average relative to the way they differ from nurse to nurse.
If two methods differ exactly the same way for all nurses, then that's the way they differ. However, if the differences between methods vary from nurse to nurse, many nurses must be examined to determine how the methods differ on average.
This makes sense at the conceptual level because the determination of a METHOD effect is accomplished by seeing how methods differ from nurse to nurse. Therefore, the more nurses the better.
Without going into too much detail, the measure of variability to which methods are compared when nurses are random behaves something like where is an expression depending on the variability in individual subjects measured under the same conditions, n is the number of subjects per cell, r is an expression depending on the variabilty between nurses, and r is the number of nurses.
There is some advantage to be had by increasing n, but clearly the big gains are to be had by increasing r. If it is known that there is no interaction between method and nurse, a simpler model can be fitted.Determining the fixed and variable expenses is the first step in performing a break-even analysis.
The number of units needed to break even = fixed costs / (price - variable costs per unit). The distinction between fixed and variable factors is related to two periods the short-run and the long-run.
The period of short-run is too short to cause variation in fixed factors. Thus, in the short-run, some factors are fixed, while the others are variable. The issue of fixed and random factors is currently making itself felt in an area called group randomized trials.
An example of a group randomized study is a comparison of teaching methods in which randomization is achieved by randomizing classes to methods.
It's much easier to budget for fixed expenses than a variable expense or discretionary expense.
Typical household fixed expenses are mortgage or rent payments, . Although production and sales volume are the main factors determining the level of variable costs incurred by a company, these costs also may fluctuate in relation to other factors, such as changes in suppliers' prices or seasonal promotional efforts.
Some expenses may . Fixed effect factor: Data has been gathered from all the levels of the factor that are of interest. Example: The purpose of an experiment is to compare the effects .