Researchers gather data, or information, using experiments and observational studies. In an experiment, a test is made under controlled conditions. Subjects in an observational study are studied without action by the investigator.
In either an experiment or an observational study, sampling is a convenient way
to gather data to make predictions about a population. A sample is a small group that is used to
represent a much larger population. Three important characteristics of a good sample
are listed below.
|
Sampling |
A good
sample is: |
A survey can be biased and give false results if these
criteria are not followed. Note that there is no given number to make the
sample large enough. You must consider each survey individually to see if it is
based on a good sample.
Example
Health Link
1. One hundred people in Lafayette,
Colorado, were asked to eat a bowl of oatmeal every day for a month to see
whether eating a healthy breakfast daily could help reduce cholesterol. After 30
days, 98 of those in the sample had lower cholesterol. Is this a good sample?
Explain. Source: Quaker Oats
Alternative Solutions :
If the
people were randomly chosen, then this is a good sample. Also, the sample
appears to be large enough to be representative of the population. For example,
the results of two or three people would not have been enough to make any
conclusions.
After the survey is complete, the gathered data is organized
into different types of tables and charts. One way to organize data is by using
a frequency table.
In a frequency table, you use tally marks to record and display the frequency of events.
Example
Science Link
2. In
an experiment, students “charged” balloons by rubbing them with wool. Then the
students placed the balloons on a wall and counted the number of seconds they
remained. The class results are shown in the chart at the right. Make a
frequency table to organize the data.
Alternative Solutions :
Step 1
Make a table with three columns:
Time (s), Tally, and Frequency.
Add a title.
Step 2
It is sometimes helpful to use intervals
so there are fewer
categories. In this case, we are using intervals of size 10.
Step 3
Use tally marks to record the times in
each interval.
Step 4
Count the tally marks in each row and
record this
number in the Frequency column.
In Example 2, suppose the science teacher wanted to know how
many
balloons stayed on the wall no more than 44 seconds. To answer this
question,
use a cumulative frequency
table in which the frequencies are accumulated for each item.
Once you have summarized data in a frequency table or in a cumulative
frequency table, you can analyze the information and make conclusions.
Example
Marketing Link
3. Owners
of a restaurant are looking for a new location. They counted the number of people
who passed by the proposed location one day during lunchtime. The frequency
table at the right shows the results of their sampling.
Alternative Solutions :
A. Which two groups of people passed by the location most frequently?
adults
in their 30s and 40s
B. If the restaurant is an ice cream shop aimed at teens during their lunchtimes, is this a good location for the restaurant? Explain.
Since
very few teens pass by the location compared to adults, the owners should
probably look for another location.
Sumber
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