The science on sleep suggests that most of us need more of it!
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A Washington Post article recently proposed that lack of sleep might be a "public health crisis." The journalist's story covered several types of empirical studies and made a series of frequency, association, and causal claims. 

Here are a series of quotes from the article. As you read each quote, ask yourself, a) How many variables seem to be involved in this claim? b) What is/are the variable(s)?  and then c) Is this claim frequency, association, or cause? How do you know? (Note: the links in each claim take you to the empirical articles on which they are based.)

Quote 1:

"Preschoolers who skip naps are worse at a memory game than those who snooze."

Quote 2:

"…a single night of sleep deprivation boosts brain levels of the proteins that form toxic clumps in Alzheimer’s patients." 

Quote 3:

"In 2016, the Centers for Disease Control and Prevention reported that a third of adults fail to get the recommended seven hours."

Quote 4:

"…even modest sleep reductions are linked to increased feelings of social isolation and loneliness."

Quote 5:

"A small study presented at the Society for Neuroscience conference last year found early evidence that playing “pink” noise — similar to white noise but with different frequencies — in a specific pattern could increase the proportion of time people spent in restorative deep sleep."

Quote 6:

"Adults over 50 with lots of insomnia symptoms were more likely to fall than those without, according to one study.:

Quote 7

"Studies have linked pain to poor sleep.."

Suggested answers to odd-numbered quotes.

Quote 1.

1. There are two variables:
2. Skipping a nap (or not) and level of skill at a memory game
3. This is an association claim, because the verb “are” is simply linking one type of preschooler (those who skip naps) with having lower skill at the memory game.

Quote 3.

1. There is one variable:
2. Getting 7 hours of sleep a night (or not)
3. This is a frequency claim. There is one variable and the sentence is mainly describing the number of U.S. adults who get that amount of sleep.

Quote 5.

1. There are two variables:
2. Playing “pink” noise (or not) and amount of time spent in restorative sleep
3. This is a causal claim because the verb used was “increase”.

Quote 7.

1. There are two variables:
2. Level of pain and quality of sleep.
3. The verb, “linked” is a verb signaling an association claim.