Posted on December 12, by Scott Alexander Aquinas famously said: For example, take medical research. Suppose a certain drug is weakly effective against a certain disease. After a few years, a bunch of different research groups have gotten their hands on it and done all sorts of different studies.
Thus the second experiment gives us 8 times as much precision for the estimate of a single item, and estimates all items simultaneously, with the same precision. What the second experiment achieves with eight would require 64 weighings if the items are weighed separately.
However, note that the estimates for the items obtained in the second experiment have errors that correlate with each other. Many problems of the design of experiments involve combinatorial designsas in this example and others. A good way to prevent biases potentially leading to false positives in the data collection phase is to use a double-blind design.
When a double-blind design is used, participants are randomly assigned to experimental groups but the researcher is unaware of what participants belong to which group.
Experimental designs with undisclosed degrees of freedom are a problem. P-hacking can be prevented by preregistering researches, in which researchers have to send their data analysis plan to the journal they wish to publish their paper in before they even start their data collection, so no data manipulation is possible https: Another way to prevent this is taking the double-blind design to the data-analysis phase, where the data are sent to a data-analyst unrelated to the research who scrambles up the data so there is no way to know which participants belong to before they are potentially taken away as outliers.
Clear and complete documentation of the experimental methodology is also important in order to support replication of results. Some of the following topics have already been discussed in the principles of experimental design section: How many factors does the design have, and are the levels of these factors fixed or random?
Are control conditions needed, and what should they be? Manipulation checks; did the manipulation really work? What are the background variables?
What is the sample size. How many units must be collected for the experiment to be generalisable and have enough power? What is the relevance of interactions between factors?
What is the influence of delayed effects of substantive factors on outcomes? How do response shifts affect self-report measures? How feasible is repeated administration of the same measurement instruments to the same units at different occasions, with a post-test and follow-up tests?
What about using a proxy pretest? Are there lurking variables? What is the feasibility of subsequent application of different conditions to the same units?
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How many of each control and noise factors should be taken into account? The independent variable of a study often has many levels or different groups. In a true experiment, researchers can have an experimental group, which is where their intervention testing the hypothesis is implemented, and a control group, which has all the same element as the experimental group, without the interventional element.
Thus, when everything else except for one intervention is held constant, researchers can certify with some certainty that this one element is what caused the observed change.
In some instances, having a control group is not ethical.
This is sometimes solved using two different experimental groups. In some cases, independent variables cannot be manipulated, for example when testing the difference between two groups who have a different disease, or testing the difference between genders obviously variables that would be hard or unethical to assign participants to.
In these cases, a quasi-experimental design may be used. Causal attributions[ edit ] In the pure experimental design, the independent predictor variable is manipulated by the researcher - that is - every participant of the research is chosen randomly from the population, and each participant chosen is assigned randomly to conditions of the independent variable.Grace and wisdom of the ages from 66 books, by 40 authors, over years, in 3 languages, on 3 continents, with 1 divinely-inspired theme of love and redemption for all mankind.
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