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Components of experiments

● 1. Control group

○ Use as a comparison group to test new drug

● 2. Placebo - an inactive drug designed to be indistinguishable from active drug

● 3. Placebo effect

○ Improvement when you “know” you are taking a drug

● 4. Single-blind

○ Control gets placebo

○ Subjects in both groups don’t know which they get

● 5. Double - blind

○ Both subjects and the evaluators don't know (“blind”) which drug they got

○ When the outcomes being measured have any degree of subjectivity, if the

person doing the measurement knows which drug the subject is getting this may

bias results

Chapter 2

● Summarizing and graphing data

○ We use frequencies and relative frequencies to summarize and graph data

● Frequency table

○ Summarizes data by grouping data values into categories

●

● Relative frequency = frequency / N

○ Relative frequency is the proportion (fraction) of values in the data

○ Ex: relative frequency for never married = 18/180 = 0.1

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○

○ Ex: a discrete random variable sample of 8 families with following numbers of

children 0,1,2,2,1,2,3,4

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○ Notice the 2 graphs have exactly the same shape. The only difference is the y-

axis

○ These graphs are called histograms

■ Histograms have 3 choices for the y-axis

● 1. Frequency

● 2. Relative frequency

● 3. Percent = relative frequency

● All 3 graphs will have same shape

● When we have data for a discrete variable (like # children) we can make a bar for every

value in the data

● When we have data for a continuous random variable we have to group the data values

into a set of intervals

● To make histogram for continuous data

○ 1. Divide values into intervals

■ Call these classes

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○ 2. Count number of data in each class

■ Counts are called frequencies

○ 3. Draw bar for each class with height using one of the following

■ Frequency = number values in class

■ Relative frequency = (frequency) / (total number values)

■ Or percent = relative frequency x 100%

○ Example of data for a continuous variable: annual incomes for n = 20 families

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