TUTORIAL



This brief tutorial describes four examples of how a Randomizer form can be used to carry out common research tasks such as drawing a random sample of individuals from a population.

The full tutorial takes about 10 minutes to complete.

LESSON 3 OF 4

Random Assignment of 40 Participants in Blocks of 4


In Lesson 2, 40 volunteers were randomly assigned to one of 4 experimental conditions, but the result was that only 7 participants ended up in Condition 1 — half the number that ended up in Condition 2. This kind of result is common in random assignment, just as tossing a coin 20 times usually leads to a different result than exactly 10 heads and 10 tails.

Unfortunately, large differences in sample size can interfere with certain statistical tests. One way around this problem is to use a "blocked design" in which participants are randomly assigned within a block of trials. In the drug experiment from Lesson 2, for example, we could divide the 40 volunteers into 10 blocks of 4 participants and then randomly assign each person within a block to one of the four experimental conditions, such as:


Block 1:

  • Participant 001: Condition 3
  • Participant 002: Condition 1
  • Participant 003: Condition 4
  • Participant 004: Condition 2

Block 2:

  • Participant 005: Condition 4
  • Participant 006: Condition 2
  • Participant 007: Condition 1
  • Participant 008: Condition 3

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To generate random numbers for this kind of blocked design, you would fill out the Randomizer form for 10 sets of 4 unique, unsorted numbers with a range from 1 to 4 (representing the four conditions). For this example, we will also use the "Place Markers Across" viewing option to simplify interpretation of the results.


Help

In some cases, you may wish to generate more than one set of numbers at a time (e.g., when randomly assigning people to experimental conditions in a "blocked" research design). If you wish to generate multiple sets of random numbers, simply enter the number of sets you want, and Research Randomizer will display all sets in the results.

Help

Specify how many numbers you want Research Randomizer to generate in each set. For example, a request for 5 numbers might yield the following set of random numbers: 2, 17, 23, 42, 50.

Help

Specify the lowest and highest value of the numbers you want to generate. For example, a range of 1 up to 50 would only generate random numbers between 1 and 50 (e.g., 2, 17, 23, 42, 50). Enter the lowest number you want in the "From" field and the highest number you want in the "To" field.

Help

Selecting "Yes" means that any particular number will appear only once in a given set (e.g., 2, 17, 23, 42, 50). Selecting "No" means that numbers may repeat within a given set (e.g., 2, 17, 17, 42, 50).
Please note: Numbers will remain unique only within a single set, not across multiple sets. If you request multiple sets, any particular number in Set 1 may still show up again in Set 2.

Help

Sorting your numbers can be helpful if you are performing random sampling, but it is not desirable if you are performing random assignment. To learn more about the difference between random sampling and random assignment, please see the Research Randomizer Quick Tutorial.

Help

Place Markers let you know where in the sequence a particular random number falls (by marking it with a small number immediately to the left).
Examples:

With Place Markers Off, your results will look something like this:
Set #1: 2, 17, 23, 42, 50
Set #2: 5, 3, 42, 18, 20
This is the default layout Research Randomizer uses.

With Place Markers Within, your results will look something like this:
Set #1: p1=2, p2=17, p3=23, p4=42, p5=50
Set #2: p1=5, p2=3, p3=42, p4=18, p5=20
This layout allows you to know instantly that the number 23 is the third number in Set #1, whereas the number 18 is the fourth number in Set #2. Notice that with this option, the Place Markers begin again at p1 in each set.

With Place Markers Across, your results will look something like this:
Set #1: p1=2, p2=17, p3=23, p4=42, p5=50
Set #2: p6=5, p7=3, p8=42, p9=18, p10=20
This layout allows you to know that 23 is the third number in the sequence, and 18 is the ninth number over both sets. As discussed in the Quick Tutorial, this option is especially helpful for doing random assignment by blocks.