Design

The design section of a lab report must do three things:

1. Clearly define the research question.
2. Identify all variables which must be controlled and describe a method for controlling them.
3. Describe a method for measuring the independent and dependent variables that allows for the collection of sufficient relevant data.

Research Question

The research question must be clearly defined.  The research question should be one sentence which includes the situation being investigated, the independent variable, and the dependent variable.  The independent variable and dependent variable must be clearly defined and must be measurable. There can be no ambiguity in the research question.   The independent variable is the variable which you change experimentally. The dependent variable is the variable which is affected by the changes in the independent variable.

Controlled Variables

Next, you must identify all factors which have an effect on your dependent variable and must be controlled.  These controlled variables should have already been discussed in the introduction.  It is important that you understand clearly the situation you will be investigating so that you will be able to identify all factors which affect your results.  For each controlled variable mentioned in the introduction, you must clearly describe what techniques were used to ensure that it stays constant during your experiment.  It is sometimes impossible to keep a variable completely constant during an investigation.  In this case you should state the range of variation which was allowed for the variable.  If a variable cannot be controlled at all, then this should be noted as a weakness of the experimental design.

Materials and Procedure

Finally, you must describe a method that allows for the collection of sufficient relevant data.  You must carefully think about what measurements you must make to get sufficient, reliable data for your independent and your dependent variables.  You must describe what actual quantities were measured and the technique which was used to measure them. (“The pH of the ethanoic acid was measured using a calibrated pH meter.”) 

You should indicate the range of values which were measured and the number of different values measured.  The range must be large enough to result in meaningful changes in the dependent variable.  If you were trying to determine how the length of a pendulum affects the time of its swing, changing a 60 cm long pendulum by 1 cm (a range of 60 cm to 61 cm) would not be good experimental design.  A good rule of thumb is to at least double your independent variable.  (“The pH was measured at six different temperatures between 10 C and 70 C.” or “The period of the pendulum was measured for six different lengths between 60 cm and 120 cm.”)  The number of trials conducted at each value of the independent variable should also be stated. (“The pH was measured three times at each temperature.”)

Illustrations or digital images of the experimental set-up should be included in this section, especially if specialized equipment is used.

Style

There are two common styles used to present the design section of a scientific report. Ask your teacher which one he/she prefers you to use.

Style 1 – Past, passive voice
Under the sub-heading of Materials and Procedure write a paragraph using past, passive voice that describes the steps used to conduct the lab in a chronological descriptive manner. Materials used to conduct the lab can be listed first or may be bold faced and within the paragraph. The writing style should be informative enough to guide a knowledgeable member of the class in repeating your experiment. Be sure to include sufficient detail. For example, do not say "Hydrochloric acid was added". Instead say "Twelve milliliters of 1.0 M Hydrochloric acid was added".

Style 2 – Imperative form
Under the sub-heading of Materials and Procedure, first list all equipment needed to do the research. Following the materials list, write numbered steps that could be used by a member of your class to conduct all the relevant steps to collect the required data. Be sure to include sufficient detail. For example, do not say "Add hydrochloric acid". Instead say "Add 12 ml of 1.0 M Hydrochloric acid". All sentences should begin with a verb and be written as a command.

Here are some examples of Research Questions and their Independent, Dependent and Controlled Variables.

Here is an example of a good Design section of a report.

 

Back to Home