Week 3: Measurement, reliability and validity Flashcards

1
Q

Explain each term regarding exposure measurement:
1. Available dose (cumulative vs current)
2. Administered dose
3. Absorbed dose/uptake
4. Active dose

A
  1. cumulative active dose = total amount given to a patient over time
    current active dose = amount given to a patient at a specific time
  2. administered dose = amount that comes in contact; can be administered in different routes
  3. absorbed dose/uptake = amount that actually enters the body
  4. active dose = how much actually had a biological effect on the target site
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2
Q

45 individuals older than 75 admitted to the hospital in Toronto for a shoulder dislocation in the past year. This is an example using the term _________

A

count

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3
Q
  1. What is ratio? Give an example
  2. What is proportion? Give an example
A
  1. ratio = relationship to COMPARE 2 numbers. The numerator is NOT necessarily included in the denominator. Ex: binary sex ratio –> 5/2 = 5:2 ratio of boys compared to girls
  2. proportion = relationship to show something OUT OF the total number. The numerator MUST be included in the denominator. Ex: binary sex proportion –> 2/4 are girls = 50% girls
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4
Q
  1. What is odd?
  2. In a population of 100 people, 25 people are diabetic. What is:
    a) the proportion of diabetes
    b) the odd of being a diabetic
A
  1. the probability of an event occurring relative to it not occurring
  2. a) proportion = 25/100 = 0.25
    b) odd = 25/75 = 0.33 –> probability of event occurring (25 people have it) over it not occurring (75 people do not have it)
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5
Q
  1. What is rate? Explain the numerator and denominator in a rate expression
  2. Write a rate for this situation: In 2021, 25 people were diagnosed with chronic bronchitis. The population at risk consisted of 1000 people.
A
  1. Rate = speed of occurrence of an event over time
    numerator = # of events observed for a given time
    denominator = population that is at risk in which the events occur –> incorporates a period of time
  2. 25/1000 = 0.025 of pop/year (2021) had chronic bronchitis
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6
Q
  1. What is prevalence rate?
  2. What are the 2 types? Explain (use formula)
A
  1. prevalence rate = proportion of the population that HAS a given disease at a specific TIME
  2. Point PR = # with disease at a specific time/ total # of people in pop at same time
    Period PR = # with disease during time period/ total # of people in pop at same time
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7
Q

If 3 million people in Canada have diabetes NOW and the current Canadian population is 30 million, what is the point PR of diabetes per 1000 people?

A

= 3 million / 30 million = 0.1 = 10% / 1 person
per 1000 = 0.1 x 1000 = 100 cases / 1000 people

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8
Q

In 2018, Montreal had a population of 152358. There were 6 cases of mononucleosis. What is the period PR of mononucleosis during 2018 per 100,000 persons?

A

Period PR = 6/152358 = 0.00004 per person x 100,000 = 4 per 100,000 persons

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9
Q
  1. What is incidence rate? Give the formula
  2. What type of studies are incidence rates obtained from:
    a) randomized controlled trials
    b) cohort (longitudinal) studies
    c) case-control studies
    d) clinical trials
A
  1. The proportion of the population AT RISK that develops a given disease or other attribute during a specified time period.
    IR = # of new cases during a specified time period/ population “at risk”
  2. b)
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10
Q

describe the relationship between prevalence and incidence and what results

A

incidence (those at risk) —> can become prevalence (those with the disease) —> which leads to the resolution (recovery or death)

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11
Q

9,000 residents of Toronto were studied on Jan 1, 2010. Of these residents, 245 had a history of cancer. By Dec 31, 2019 a total of 179 new cases of cancer had been diagnosed in the “at risk” population. What is the 10-year cumulative incidence rate of cancer (first diagnosis) in this cohort per 10,000 people?

A

IR = 179 / (9000-245) = 0.02 x 10,000 = 204 per 10,000 people.

*the at risk population (denominator) is the total pop - those who have already had cancer since we need to find a first diagnosis IR.

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12
Q

2,012 first year university students were sampled in Sept 2021. Of these, 112 had depression. In May 2022, 345 of the sample had depression, including 79 of those who had depression in September.

a) What was the prevalence of depression Sept 2021 and May 2022?
b) How many “resolution” cases were there?
c) What is the IR of new depression cases during the freshman year (Sept 2021 to May 2022) ***don’t understand answer
d) why do we remove those with depression diagnosed at the beginning of the study from the population at risk in part c)?

A

a) Sept 2021 IR= 112/2012 = 0.056 = 5.6%
May 2022 IR= 345/2012 = 0.17 = 17%

b) 112 - 79 =33

c) IR= (345-79)/ (2012-112) = 266/1900 = 0.14 = 14%

d) because these people have already had depression so they can not be at risk of developing a NEW case of depression. So they are excluded from the population at risk (denominator)

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13
Q

Incidence measures frequency of disease _______. Prevalence measures population disease _______

A

onset
status

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14
Q
  1. What is relative risk?
  2. relative risk tells us the _______ of an association
  3. What does relative risk NOT tell us?
  4. How is it calculated?
A
  1. tells us how many times as likely it is that someone who is “exposed” to something will experience a specific outcome compared to someone not exposed
  2. Strength
  3. does NOT tell us anything about how much MORE disease is occurring
  4. Make the table, will be incidence in exposed/incidence in unexposed
    RR= [a/(a+b)] / [c/(c+d)]
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15
Q

The results of a study evaluating the effects of calling patients and their likelihood to receive a influenza immunization revealed:

  • those who received a call and got immunized = 328
  • those who received no call and got immunized = 288
  • those who received a call and did not get immunized = 332
  • those who did received no call and did not get immunized = 370

What is the RR of those who received a call compared to those who did not. What do the results indicate?

A

exposure = receiving a call
outcome = getting immunized

RR= [328 / (328+332)]/[288 / (288+370)] = (328/660) / (288/658) = 0.49/0.43 = 1.14 or 14% more likely to attend for immunization

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16
Q

20,000 men without heart disease were identified in Sept 2015. Of these, 3,614 were smokers and 16,386 were non-smokers. Over a 5 year follow-up period, 552 of the smokers and 1,431 of the non-smokers developed heart disease.
Fill out the table and calculate the RR of heart disease in smokers relative to non-smokers

A

RR = 1.76 = 76%

17
Q
  1. what is random error?
  2. What is systematic error?
  3. systematic error = ____
  4. T/F: it is not possible to have both random and systematic error
A
  1. error due to chance
  2. error due to a recognizable source
  3. bias
  4. F. it is possible
18
Q

A measurement with high precision is ______
A measurement with high accuracy is ______

A

reliable
valid

19
Q

What are the results of measurements that are classified as…. (explain in terms of reliability and validity)
a) high accuracy, high precision
b) low accuracy, high precision
c) high accuracy, low precision
d) low accuracy, low precision

A

a) valid, reliable
b) not valid, reliable
c) valid, not reliable
d) not valid, not reliable

20
Q

Why would there be insufficient precision?

A
  • measurement tool is not precise enough
  • 2 separate interviewers rate the same person differently using the same scale
  • same interviewer rates the same person differently
21
Q

Identify the types of measurement error that could occur from these sources:
1. interviewer or observer
2. participants

A
  1. random error, biased over or underestimation
  2. recall bias, random or systemic error
22
Q

Identify the most likely sources of measurement error in the following situations:
a) Asking mothers with preterm birth if they were exposed to pesticide during pregnancy

b) Using 1st year psychology students to administer a questionnaire about depression without any training

c) Using only ‘students with a history of depression’ for b)

d) Asking a group of older adults about the number of their friends in high school

A

a) recall bias - participant error
b) biased under or over estimation - interviewer error
c) biased over estimation - interviewer error
d) recall bias - participant error

23
Q
  1. What is misclassification?
  2. what are the 2 types? Explain both and what happens to the association between exposure and outcome
A
  1. classifying participants into the wrong exposure or outcome group
  2. non-differential = the same misclassification in all study groups. this weakens associations and can bring the calculation (RR, OR etc.) closer to the null value (no association between outcome and exposure)

differential = different misclassification in the study groups. Associations can change in any directions

24
Q

Non-differential misclassification is often due to _______ measurement error

Differential misclassification is often due to ________ measurement error

A

random (due to chance)
systemic (locate the source)

25
Q

What are controls vs cases?

A

controls = no disease
cases = disease

26
Q

Results of a study showed:
exposed + case = 300
unexposed + case = 100
exposed + control = 250
unexposed + control = 150

  1. Draw the table, calculate the OR
  2. It was found that 10% of all exposed cases and exposed controls were misclassified as unexposed & vice versa (10% of unexposed cases and unexposed controls were misclassified as exposed). Update/fix the data. What type of misclassification occurred? What happened to the OR as a result?
  3. It was found that 20% of unexposed cases (but not controls) were misclassified as exposed. What type of misclassification occurred? What happened to the OR as a result?
A
  1. OR = 1.8
  2. non-differential misclassification. new OR = 1.6 meaning its closer to the null (weakened association created)
  3. differential misclassification. new OR = 2.4 meaning its further from the null in this situation (stronger association created)
27
Q

T/F: Information bias can be fixed once it has occurred

A

F