Theories are incomplete, temporary ideas. A theory never changes. Theories are inferred explanations, strongly supported by evidence. A scientific law has been proven and a theory has not.

An example of a scientific law is the law of conservation of mass, which states that matter is neither created nor destroyed in a chemical reaction.

Other examples of laws in physical science include:

• Newton’s first law of motion.
• Newton’s second law of motion.
• Newton’s law of universal gravitation.
• Law of conservation of mass.
• Law of conservation of energy.
• Law of conservation of momentum.

An accepted scientific theory could still be proven wrong.

Scientific models are used to explain and predict the behaviour of real objects or systems and are used in a variety of scientific disciplines, ranging from physics and chemistry to ecology and the Earth sciences.

Scientific theory: a well-tested concept that explains a wide range of observations. Scientific law: a statement that describes what scientists expect to happen every time under a particular set of conditions.

In popular use, a theory is often assumed to imply mere speculation, but in science, something is not called a theory until it has been confirmed over many independent experiments. Theories are more certain than hypotheses, but less certain than laws.

In general, however, a good research question should be:

• Clear and focused. In other words, the question should clearly state what the writer needs to do.
• Not too broad and not too narrow.
• Not too easy to answer.
• Not too difficult to answer.
• Researchable.
• Analytical rather than descriptive.

Furthermore, despite the increasing guidelines for effectively conducting a systematic review, we found that basic steps often start from framing question, then identifying relevant work which consists of criteria development and search for articles, appraise the quality of included studies, summarize the evidence, and …

Systematic reviews offer a number of benefits. For starters, they deliver a clear and comprehensive overview of available evidence on a given topic. Moreover, SRs also help identify research gaps in our current understanding of a field.

Steps for writing a systematic review

1. Formulate a research question. Consider whether a systematic review is needed before starting your project.
2. Develop research protocol.
3. Conduct literature search.
4. Select studies per protocol.
5. Appraise studies per protocol.
6. Extract data.
7. Analyze results.
8. Interpret results.

Steps to a Systematic Review

• Formulate a question.
• Develop protocol.
• Conduct search.
• Select studies and assess study quality.
• Extract data and analyze/summarize and synthesize relevant studies.
• Interpret results.