The four types of validity

When you do quantitative research, you have to consider the reliability and validity of your methods and instruments of measurement.

Validity tells you how accurately a method measures something. If a method measures what it claims to measure, and the results closely correspond to real-world values, then it can be considered valid. There are four main types of validity:

Note that this article deals with types of test validity, which determine the accuracy of the actual components of a measure. If you are doing experimental research, you also need to consider internal and external validity, which deal with the experimental setup and the generalizability of results.

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Types of reliability and how to measure them

When you do quantitative research, you have to consider the reliability and validity of your methods and instruments of measurement.

Reliability tells you how consistently a method measures something. When you apply the same method to the same sample under the same conditions, you should get the same results. If not, the method of measurement may be unreliable.

There are four main types of reliability. Each can be estimated by comparing different sets of results produced by the same method.

Reliability
Type of reliabilityMeasures the consistency of…
Test-retestThe same test over time.
InterraterThe same test conducted by different people.
Parallel formsDifferent versions of a test which are designed to be equivalent.
Internal consistencyThe individual items of a test.

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Reliability vs validity: what’s the difference?

Reliability and validity are concepts used to evaluate the quality of research. They indicate how well a method, technique or test measures something. Reliability is about the consistency of a measure, and validity is about the accuracy of a measure.

It’s important to consider reliability and validity when you are creating your research design, planning your methods, and writing up your results, especially in quantitative research.

Reliability vs validity
ReliabilityValidity
What does it tell you?The extent to which the results can be reproduced when the research is repeated under the same conditions.The extent to which the results really measure what they are supposed to measure.
How is it assessed?By checking the consistency of results across time, across different observers, and across parts of the test itself.By checking how well the results correspond to established theories and other measures of the same concept.
How do they relate?A reliable measurement is not always valid: the results might be reproducible, but they’re not necessarily correct.A valid measurement is generally reliable: if a test produces accurate results, they should be reproducible.

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Recognizing and using uncountable nouns

Uncountable nouns, also known as mass nouns or noncount nouns, refer to a mass of something or an abstract concept that can’t be counted (except with a unit of measurement). In contrast, countable nouns can be counted as individual items.

The main rules to remember for uncountable nouns are that they cannot be pluralized, and that they never take indefinite articles (a or an).

Common examples of uncountable nouns
Type of nounExamples
Abstract concepts and physical phenomenaresearch, advice, information, knowledge, money, logic, gravity, acceleration, pollution, feedback, traffic, radiation, biomass, lightning
Substances, materials and foodsair, water, blood, algae, mud, grass, seaweed, graphite, clay, quartz, rice, flour, meat
Elements, chemicals and gaseshelium, iron, copper, hydrochloric acid, calcium carbonate, carbon monoxide, methane
Disciplines and fieldsbiology, chemistry, physics, mathematics, geography, psychology, economics, aquaculture, trigonometry

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Apostrophes (’)

Apostrophes have two main uses:

  • Indicating possession (e.g. The student’s paper)
  • Indicating a contraction (e.g. She’s writing a paper)

Contractions should be avoided in academic writing, but possessive apostrophes are used in all types of writing. Make sure to use them correctly, especially when dealing with plurals and abbreviations.

Use a possessive apostrophe…
This study examines the company’s efforts to expand.
I highly recommend Sharon’s salon.
My parents’ support was essential.
The crowd’s applause could be heard for miles.
In the last quarter, BP’s profits dropped.
Don’t use an apostrophe…
The results are surprising.
Remember what happened three Christmases ago?
Several NGOs were present at the conference.
We can identify the following KPIs.
The 1920s was a golden age for art.
During the 2010s politics slid into confusion.
The cobra reared its head.
Whose snake is that?

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Commas (,)

Commas are used to split up different parts of a sentence, and when used correctly they bring clarity and flow to your writing. They’re probably the most common piece of punctuation in English, which means that they’re often the most misused.

This article takes you through the most important comma rules and the most common mistakes.

When to use a comma
  • Incorrect
  • Correct
Introducing a sentenceAdditionally the project was delayed.Additionally, the project was delayed.
Separating a nonrestrictive clauseMatilda who was unloved by her family escaped from reality by reading.Matilda, who was unloved by her family, escaped from reality by reading.
Joining independent clauses with a coordinating conjunctionOysters are considered a luxury product so they are expensive.Oysters are considered a luxury product, so they are expensive.
When not to use a comma
  • Incorrect
  • Correct
Between a verb and its subjectThis desk, is too small.This desk is too small.
Between compound subjects or objectsA stack of pancakes, and a lot of coffee make for a delicious breakfast.A stack of pancakes and a lot of coffee make for a delicious breakfast.
Between compound predicatesWe distributed questionnaires, and conducted interviews.We distributed questionnaires and conducted interviews.
Between independent clausesProfits fell, the company collapsed.Profits fell; the company collapsed.

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Choosing the right prepositions

Prepositions are words that show the relationship between elements in a sentence. They can express relationships of place, time, direction, and other abstract or logical connections.

A preposition is usually located directly before the word or phrase that it relates to – the object of the preposition.

  • We walked to the shop.
  • I’ve been unwell since last Wednesday.
  • That gift is for him.

Prepositions are flexible words that are often central to the meaning of a sentence, and it can be tricky to choose the right one. The best way to master them is by reading and practice.

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Subject-verb agreement

The subject of a sentence should always match the verb describing its action. This helps your reader understand who or what is doing something and makes your writing easier to read.

First, identify the subject (the person or thing doing the action) and the verb (the action word) in a sentence. If the subject is singular, the verb describing its action should be singular. If the subject is plural, the verb should be plural.

VerbSingular subject + verbPlural subject + verb
BeThe result is significant.The results are significant.
DoThe student does her best.The students do their best.
BecomeThe child becomes happier.The children become happier.
CauseThat tree causes hay fever.Those trees cause hay fever.
AnalyzeThe author analyzes the text.The authors analyze the text.

While subject-verb agreement is easy in simple sentences like these, it can become tricky in more complex sentences. This article teaches you the most important rules and common mistakes.

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