Question

1. The authors claim that random assignment is “the key to eliminating all possible confounds in a true experiment.” however this is not correct. Can you think of a type of confound that would not be eliminated by random assignment? Can I please get an example?
2. Is it possible to use a ratio scale to measure a psychological construct like Anger or Happiness? If so, give an example. If not, explain why not.

Thank you for your help!

Answer 1

1. Random assignment refers to the use of chance procedures in psychology experiments to ensure that each participant has the same opportunity to be assigned to any given group. Study participants are randomly assigned to different groups, such as the experimental group or treatment group. Random assignment, blinding, and controlling are key aspects of the design of experiments, because they help ensure that the results are not spurious or deceptive via confounding. This is why randomized controlled trials are vital in clinical research, especially ones that can be double-blinded and placebo-controlled.

Random assignment does not guarantee that the groups are matched or equivalent. The groups may still differ on some preexisting attribute due to chance. The use of random assignment cannot eliminate this possibility, but it greatly reduces it. To express this same idea statistically - If a randomly assigned group is compared to the mean it may be discovered that they differ, even though they were assigned from the same group. If a test of statistical significance is applied to randomly assigned groups to test the difference between sample means against the null hypothesis that they are equal to the same population mean (i.e., population mean of differences = 0), given the probability distribution, the null hypothesis will sometimes be "rejected," that is, deemed not plausible. That is, the groups will be sufficiently different on the variable tested to conclude statistically that they did not come from the same population, even though, procedurally, they were assigned from the same total group. For example, using random assignment may create an assignment to groups that has 20 blue-eyed people and 5 brown-eyed people in one group. This is a rare event under random assignment, but it could happen, and when it does it might add some doubt to the causal agent in the experimental hypothesis.

2. Ratio scale refers to the level of measurement in which the attributes composing variables are measured on specific numerical scores or values that have equal distances between attributes or points along the scale and are based on a “true zero” point. Among four levels of measurement, including nominal, ordinal, interval, and ratio scales, the ratio scale is the most precise. Because attributes in a ratio scale have equal distances and a true zero point, statements about the ratio of attributes can be made. The score of zero in a ratio scale is not arbitrary, and it indicates the absence of whatever is being measured. Most variables in experimental sciences, particularly in behavioral sciences and natural sciences, are ratio-scale variables.

With help of above explanation it can be concluded that for happiness there can never be 'true zero' value and same can be said for love. there will always be a degree whether 1 or 100. We cannot measure happiness or love upto precision it will always go in approaximation.