1 / 31

Biostatistics Basics

An introduction to an expansive and complex field. Biostatistics Basics. Variable Types. Independent variables Precede dependent variables in time Manipulated by the researcher Usually Tx or Intervention Dependent variables Outcome measures Depends on the independent variable.

bevis
Download Presentation

Biostatistics Basics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. An introduction to an expansive and complex field Biostatistics Basics

  2. Evidence-based Chiropractic Variable Types Independent variables Precede dependent variables in time Manipulated by the researcher Usually Tx or Intervention Dependent variables Outcome measures Depends on the independent variable

  3. Evidence-based Chiropractic Populations A population is the group from which a sample is drawn e.g., headache patients in a chiropractic office; automobile crash victims in an emergency room Practicality of inclusion Sample (a subset of a population)

  4. Evidence-based Chiropractic Random samples Selection method– equal chance or bias? Random samples are representative of the source population Non-random samples are not representative May be biased regarding age, severity of the condition, socioeconomic status etc.

  5. Evidence-based Chiropractic Random samples (cont.) Limited practicality in healthcare research Randomly assigned to treatment and control groups Equal chance Random assignment is also known as randomization

  6. Evidence-based Chiropractic Descriptive statistics (DSs) A way to summarize data from a sample or a population DSs vs Inferential statistics DSs are not capable of testing hypotheses DSs illustrate the shape, central tendency, and variability of a set of data

  7. Evidence-based Chiropractic DSs terms The shape of data frequencies of the values of observations Central tendency location of the middle of the data Variability Spread or Dispersion

  8. Hypothetical study data(partial from book) Case # Visits 1 7 2 2 3 2 4 3 5 4 6 3 7 5 8 3 9 4 10 6 11 2 12 3 13 7 14 4 • Distribution provides a summary of: • Frequencies of each of the values • 2 – 3 • 3 – 4 • 4 – 3 • 5 – 1 • 6 – 1 • 7 – 2 • Ranges of values • Lowest = 2 • Highest = 7 etc. Evidence-based Chiropractic

  9. Frequency distribution table • FrequencyPercentCumulative % • 2 3 21.4 21.4 • 3 4 28.6 50.0 • 4 3 21.4 71.4 • 5 1 7.1 78.5 • 6 1 7.1 85.6 • 7 2 14.3 100.0 Evidence-based Chiropractic

  10. Evidence-based Chiropractic Frequency distributions are often depicted by a histogram

  11. Evidence-based Chiropractic Histograms (cont.) Histograms visually depict frequency distributions of continuous data Bar charts are used to depict categorical information e.g., Male–Female, Mild–Moderate–Severe, etc. Thus, the separation

  12. Evidence-based Chiropractic Measures of central tendency Mean (a.k.a., average) The most commonly used DS Mode The most frequently occurring value in a series Median The value that divides a series of values in half when they are all listed in order

  13. Evidence-based Chiropractic Measures of central tendency (cont.) Each of the three methods of measuring central tendency has certain advantages and disadvantages Which method should be used? It depends on the type of data that is being analyzed e.g., categorical, continuous, and the level of measurement that is involved

  14. Evidence-based Chiropractic Levels of measurement There are 4 levels of measurement NOIR is a mnemonic to help remember the names and order of the levels of measurement Nominal – By name/label (Gender, Therapy) Ordinal – ordered rank (Severity, Military) Interval – equal intervals (F, VAS) Ratio – true zero (ROM, K)

  15. Levels of measurement (cont.) Evidence-based Chiropractic

  16. Evidence-based Chiropractic The shape of data Histograms of frequency distributions have shape Distributions are often symmetrical with most scores falling in the middle and fewer toward the extremes Most biological data are symmetrically distributed and form a normalcurve (a.k.a, bell-shaped curve)

  17. Evidence-based Chiropractic The shape of data (cont.) Line depicting the shape of the data

  18. Evidence-based Chiropractic The normal distribution The area under a normal curve has a normal distribution (a.k.a., Gaussian distribution) Properties of a normal distribution It is symmetric about its mean The highest point is at its mean The height of the curve decreases as one moves away from the mean in either direction, approaching, but never reaching zero

  19. Evidence-based Chiropractic The normal distribution (cont.) Mean The highest point of the overlying normal curve is at the mean As one moves away from the mean in either direction the height of the curve decreases, approaching, but never reaching zero A normal distribution is symmetric about its mean

  20. Evidence-based Chiropractic The normal distribution (cont.) Mean = Median = Mode

  21. Evidence-based Chiropractic Skewed distributions The data are not distributed symmetrically in skewed distributions Consequently, the mean, median, and mode are not equal and are in different positions Scores are clustered at one end of the distribution A small number of extreme values are located in the limits of the opposite end

  22. Evidence-based Chiropractic Skewed distributions (cont.) Skew is always toward the direction of the longer tail Positive if skewed to the right Negative if to the left The mean is shifted the most

  23. Evidence-based Chiropractic Skewed distributions (cont.) Because the mean is shifted so much, it is not the best estimate of the average score for skewed distributions The median is a better estimate of the center of skewed distributions It will be the central point of any distribution 50% of the values are above and 50% below the median

  24. Evidence-based Chiropractic More properties of normal curves About 68.3% of the area under a normal curve is within one standard deviation (SD) of the mean About 95.5% is within two SDs About 99.7% is within three SDs

  25. Evidence-based Chiropractic More properties of normal curves (cont.)

  26. Evidence-based Chiropractic Standard deviation (SD) SD is a measure of the variability of a set of data The mean represents the average of a group of scores, with some of the scores being above the mean and some below This range of scores is referred to as variability or spread

  27. Evidence-based Chiropractic z-scores The number of SDs that a specific score is above or below the mean in a distribution The proportion of scores that are higher or lower than a specific z-score can be determined by referring to a z-table

  28. Evidence-based Chiropractic z-scores (cont.) Refer to a z-tableto find proportionunder the curve

  29. Evidence-based Chiropractic z-scores (cont.) Corresponds to the area under the curve in black 0.9332

  30. Evidence-based Chiropractic Wide spread results in higher SDs narrow spread in lower SDs

  31. Evidence-based Chiropractic Spread is important when comparing 2 or more group means It is more difficult to see a clear distinctionbetween groups in the upper example because the spread is wider, even though the means are the same

More Related